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![Brian Bloniarz](/assets/img/avatar_default.png)
OpenSSH expects the (non-blocking) read() of pty master to return EAGAIN only if it has received all of the slave-side output after it has received SIGCHLD. This used to work on pre-3.12 kernels. This fix effectively forces non-blocking read() and poll() to block for parallel i/o to complete for all ttys. It also unwinds these changes: 1)f8747d4a46
tty: Fix pty master read() after slave closes 2)52bce7f8d4
pty, n_tty: Simplify input processing on final close 3)1a48632ffe
pty: Fix input race when closing Inspired by analysis and patch from Marc Aurele La France <tsi@tuyoix.net> Reported-by: Volth <openssh@volth.com> Reported-by: Marc Aurele La France <tsi@tuyoix.net> BugLink: https://bugzilla.mindrot.org/show_bug.cgi?id=52 BugLink: https://bugzilla.mindrot.org/show_bug.cgi?id=2492 Signed-off-by: Brian Bloniarz <brian.bloniarz@gmail.com> Reviewed-by: Peter Hurley <peter@hurleysoftware.com> Cc: stable <stable@vger.kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
594 lines
16 KiB
C
594 lines
16 KiB
C
/*
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* Tty buffer allocation management
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*/
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#include <linux/types.h>
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#include <linux/errno.h>
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#include <linux/tty.h>
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#include <linux/tty_driver.h>
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#include <linux/tty_flip.h>
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#include <linux/timer.h>
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#include <linux/string.h>
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#include <linux/slab.h>
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#include <linux/sched.h>
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#include <linux/wait.h>
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#include <linux/bitops.h>
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#include <linux/delay.h>
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#include <linux/module.h>
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#include <linux/ratelimit.h>
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#define MIN_TTYB_SIZE 256
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#define TTYB_ALIGN_MASK 255
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/*
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* Byte threshold to limit memory consumption for flip buffers.
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* The actual memory limit is > 2x this amount.
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*/
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#define TTYB_DEFAULT_MEM_LIMIT 65536
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/*
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* We default to dicing tty buffer allocations to this many characters
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* in order to avoid multiple page allocations. We know the size of
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* tty_buffer itself but it must also be taken into account that the
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* the buffer is 256 byte aligned. See tty_buffer_find for the allocation
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* logic this must match
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*/
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#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
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/**
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* tty_buffer_lock_exclusive - gain exclusive access to buffer
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* tty_buffer_unlock_exclusive - release exclusive access
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*
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* @port - tty_port owning the flip buffer
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*
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* Guarantees safe use of the line discipline's receive_buf() method by
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* excluding the buffer work and any pending flush from using the flip
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* buffer. Data can continue to be added concurrently to the flip buffer
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* from the driver side.
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*
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* On release, the buffer work is restarted if there is data in the
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* flip buffer
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*/
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void tty_buffer_lock_exclusive(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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atomic_inc(&buf->priority);
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mutex_lock(&buf->lock);
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}
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EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
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void tty_buffer_unlock_exclusive(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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int restart;
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restart = buf->head->commit != buf->head->read;
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atomic_dec(&buf->priority);
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mutex_unlock(&buf->lock);
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if (restart)
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queue_work(system_unbound_wq, &buf->work);
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}
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EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
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/**
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* tty_buffer_space_avail - return unused buffer space
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* @port - tty_port owning the flip buffer
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*
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* Returns the # of bytes which can be written by the driver without
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* reaching the buffer limit.
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*
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* Note: this does not guarantee that memory is available to write
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* the returned # of bytes (use tty_prepare_flip_string_xxx() to
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* pre-allocate if memory guarantee is required).
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*/
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int tty_buffer_space_avail(struct tty_port *port)
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{
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int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
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return max(space, 0);
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}
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EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
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static void tty_buffer_reset(struct tty_buffer *p, size_t size)
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{
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p->used = 0;
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p->size = size;
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p->next = NULL;
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p->commit = 0;
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p->read = 0;
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p->flags = 0;
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}
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/**
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* tty_buffer_free_all - free buffers used by a tty
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* @tty: tty to free from
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*
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* Remove all the buffers pending on a tty whether queued with data
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* or in the free ring. Must be called when the tty is no longer in use
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*/
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void tty_buffer_free_all(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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struct tty_buffer *p, *next;
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struct llist_node *llist;
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while ((p = buf->head) != NULL) {
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buf->head = p->next;
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if (p->size > 0)
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kfree(p);
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}
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llist = llist_del_all(&buf->free);
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llist_for_each_entry_safe(p, next, llist, free)
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kfree(p);
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tty_buffer_reset(&buf->sentinel, 0);
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buf->head = &buf->sentinel;
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buf->tail = &buf->sentinel;
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atomic_set(&buf->mem_used, 0);
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}
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/**
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* tty_buffer_alloc - allocate a tty buffer
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* @tty: tty device
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* @size: desired size (characters)
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*
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* Allocate a new tty buffer to hold the desired number of characters.
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* We round our buffers off in 256 character chunks to get better
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* allocation behaviour.
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* Return NULL if out of memory or the allocation would exceed the
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* per device queue
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*/
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static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
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{
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struct llist_node *free;
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struct tty_buffer *p;
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/* Round the buffer size out */
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size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
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if (size <= MIN_TTYB_SIZE) {
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free = llist_del_first(&port->buf.free);
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if (free) {
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p = llist_entry(free, struct tty_buffer, free);
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goto found;
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}
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}
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/* Should possibly check if this fails for the largest buffer we
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have queued and recycle that ? */
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if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
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return NULL;
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p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
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if (p == NULL)
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return NULL;
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found:
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tty_buffer_reset(p, size);
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atomic_add(size, &port->buf.mem_used);
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return p;
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}
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/**
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* tty_buffer_free - free a tty buffer
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* @tty: tty owning the buffer
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* @b: the buffer to free
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*
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* Free a tty buffer, or add it to the free list according to our
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* internal strategy
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*/
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static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
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{
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struct tty_bufhead *buf = &port->buf;
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/* Dumb strategy for now - should keep some stats */
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WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
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if (b->size > MIN_TTYB_SIZE)
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kfree(b);
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else if (b->size > 0)
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llist_add(&b->free, &buf->free);
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}
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/**
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* tty_buffer_flush - flush full tty buffers
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* @tty: tty to flush
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* @ld: optional ldisc ptr (must be referenced)
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*
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* flush all the buffers containing receive data. If ld != NULL,
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* flush the ldisc input buffer.
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*
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* Locking: takes buffer lock to ensure single-threaded flip buffer
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* 'consumer'
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*/
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void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
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{
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struct tty_port *port = tty->port;
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struct tty_bufhead *buf = &port->buf;
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struct tty_buffer *next;
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atomic_inc(&buf->priority);
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mutex_lock(&buf->lock);
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/* paired w/ release in __tty_buffer_request_room; ensures there are
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* no pending memory accesses to the freed buffer
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*/
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while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
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tty_buffer_free(port, buf->head);
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buf->head = next;
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}
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buf->head->read = buf->head->commit;
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if (ld && ld->ops->flush_buffer)
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ld->ops->flush_buffer(tty);
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atomic_dec(&buf->priority);
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mutex_unlock(&buf->lock);
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}
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/**
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* tty_buffer_request_room - grow tty buffer if needed
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* @tty: tty structure
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* @size: size desired
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* @flags: buffer flags if new buffer allocated (default = 0)
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*
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* Make at least size bytes of linear space available for the tty
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* buffer. If we fail return the size we managed to find.
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*
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* Will change over to a new buffer if the current buffer is encoded as
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* TTY_NORMAL (so has no flags buffer) and the new buffer requires
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* a flags buffer.
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*/
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static int __tty_buffer_request_room(struct tty_port *port, size_t size,
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int flags)
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{
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struct tty_bufhead *buf = &port->buf;
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struct tty_buffer *b, *n;
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int left, change;
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b = buf->tail;
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if (b->flags & TTYB_NORMAL)
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left = 2 * b->size - b->used;
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else
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left = b->size - b->used;
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change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
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if (change || left < size) {
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/* This is the slow path - looking for new buffers to use */
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n = tty_buffer_alloc(port, size);
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if (n != NULL) {
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n->flags = flags;
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buf->tail = n;
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/* paired w/ acquire in flush_to_ldisc(); ensures
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* flush_to_ldisc() sees buffer data.
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*/
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smp_store_release(&b->commit, b->used);
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/* paired w/ acquire in flush_to_ldisc(); ensures the
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* latest commit value can be read before the head is
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* advanced to the next buffer
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*/
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smp_store_release(&b->next, n);
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} else if (change)
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size = 0;
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else
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size = left;
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}
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return size;
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}
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int tty_buffer_request_room(struct tty_port *port, size_t size)
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{
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return __tty_buffer_request_room(port, size, 0);
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}
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EXPORT_SYMBOL_GPL(tty_buffer_request_room);
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/**
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* tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
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* @port: tty port
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* @chars: characters
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* @flag: flag value for each character
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* @size: size
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*
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* Queue a series of bytes to the tty buffering. All the characters
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* passed are marked with the supplied flag. Returns the number added.
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*/
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int tty_insert_flip_string_fixed_flag(struct tty_port *port,
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const unsigned char *chars, char flag, size_t size)
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{
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int copied = 0;
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do {
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int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
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int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
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int space = __tty_buffer_request_room(port, goal, flags);
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struct tty_buffer *tb = port->buf.tail;
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if (unlikely(space == 0))
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break;
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memcpy(char_buf_ptr(tb, tb->used), chars, space);
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if (~tb->flags & TTYB_NORMAL)
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memset(flag_buf_ptr(tb, tb->used), flag, space);
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tb->used += space;
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copied += space;
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chars += space;
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/* There is a small chance that we need to split the data over
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several buffers. If this is the case we must loop */
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} while (unlikely(size > copied));
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return copied;
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}
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EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
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/**
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* tty_insert_flip_string_flags - Add characters to the tty buffer
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* @port: tty port
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* @chars: characters
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* @flags: flag bytes
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* @size: size
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*
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* Queue a series of bytes to the tty buffering. For each character
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* the flags array indicates the status of the character. Returns the
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* number added.
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*/
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int tty_insert_flip_string_flags(struct tty_port *port,
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const unsigned char *chars, const char *flags, size_t size)
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{
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int copied = 0;
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do {
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int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
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int space = tty_buffer_request_room(port, goal);
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struct tty_buffer *tb = port->buf.tail;
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if (unlikely(space == 0))
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break;
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memcpy(char_buf_ptr(tb, tb->used), chars, space);
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memcpy(flag_buf_ptr(tb, tb->used), flags, space);
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tb->used += space;
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copied += space;
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chars += space;
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flags += space;
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/* There is a small chance that we need to split the data over
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several buffers. If this is the case we must loop */
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} while (unlikely(size > copied));
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return copied;
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}
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EXPORT_SYMBOL(tty_insert_flip_string_flags);
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/**
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* tty_schedule_flip - push characters to ldisc
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* @port: tty port to push from
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*
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* Takes any pending buffers and transfers their ownership to the
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* ldisc side of the queue. It then schedules those characters for
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* processing by the line discipline.
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*/
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void tty_schedule_flip(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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/* paired w/ acquire in flush_to_ldisc(); ensures
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* flush_to_ldisc() sees buffer data.
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*/
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smp_store_release(&buf->tail->commit, buf->tail->used);
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queue_work(system_unbound_wq, &buf->work);
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}
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EXPORT_SYMBOL(tty_schedule_flip);
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/**
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* tty_prepare_flip_string - make room for characters
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* @port: tty port
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* @chars: return pointer for character write area
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* @size: desired size
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*
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* Prepare a block of space in the buffer for data. Returns the length
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* available and buffer pointer to the space which is now allocated and
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* accounted for as ready for normal characters. This is used for drivers
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* that need their own block copy routines into the buffer. There is no
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* guarantee the buffer is a DMA target!
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*/
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int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
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size_t size)
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{
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int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
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if (likely(space)) {
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struct tty_buffer *tb = port->buf.tail;
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*chars = char_buf_ptr(tb, tb->used);
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if (~tb->flags & TTYB_NORMAL)
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memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
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tb->used += space;
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}
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return space;
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}
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EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
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/**
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* tty_ldisc_receive_buf - forward data to line discipline
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* @ld: line discipline to process input
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* @p: char buffer
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* @f: TTY_* flags buffer
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* @count: number of bytes to process
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*
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* Callers other than flush_to_ldisc() need to exclude the kworker
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* from concurrent use of the line discipline, see paste_selection().
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*
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* Returns the number of bytes not processed
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*/
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int tty_ldisc_receive_buf(struct tty_ldisc *ld, unsigned char *p,
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char *f, int count)
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{
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if (ld->ops->receive_buf2)
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count = ld->ops->receive_buf2(ld->tty, p, f, count);
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else {
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count = min_t(int, count, ld->tty->receive_room);
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if (count && ld->ops->receive_buf)
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ld->ops->receive_buf(ld->tty, p, f, count);
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}
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return count;
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}
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EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
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static int
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receive_buf(struct tty_ldisc *ld, struct tty_buffer *head, int count)
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{
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unsigned char *p = char_buf_ptr(head, head->read);
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char *f = NULL;
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if (~head->flags & TTYB_NORMAL)
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f = flag_buf_ptr(head, head->read);
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return tty_ldisc_receive_buf(ld, p, f, count);
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}
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/**
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* flush_to_ldisc
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* @work: tty structure passed from work queue.
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*
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* This routine is called out of the software interrupt to flush data
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* from the buffer chain to the line discipline.
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*
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* The receive_buf method is single threaded for each tty instance.
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*
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* Locking: takes buffer lock to ensure single-threaded flip buffer
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* 'consumer'
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*/
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static void flush_to_ldisc(struct work_struct *work)
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{
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struct tty_port *port = container_of(work, struct tty_port, buf.work);
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struct tty_bufhead *buf = &port->buf;
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struct tty_struct *tty;
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struct tty_ldisc *disc;
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tty = READ_ONCE(port->itty);
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if (tty == NULL)
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return;
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disc = tty_ldisc_ref(tty);
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if (disc == NULL)
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return;
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mutex_lock(&buf->lock);
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while (1) {
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struct tty_buffer *head = buf->head;
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struct tty_buffer *next;
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int count;
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/* Ldisc or user is trying to gain exclusive access */
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if (atomic_read(&buf->priority))
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break;
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/* paired w/ release in __tty_buffer_request_room();
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* ensures commit value read is not stale if the head
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* is advancing to the next buffer
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*/
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next = smp_load_acquire(&head->next);
|
|
/* paired w/ release in __tty_buffer_request_room() or in
|
|
* tty_buffer_flush(); ensures we see the committed buffer data
|
|
*/
|
|
count = smp_load_acquire(&head->commit) - head->read;
|
|
if (!count) {
|
|
if (next == NULL)
|
|
break;
|
|
buf->head = next;
|
|
tty_buffer_free(port, head);
|
|
continue;
|
|
}
|
|
|
|
count = receive_buf(disc, head, count);
|
|
if (!count)
|
|
break;
|
|
head->read += count;
|
|
}
|
|
|
|
mutex_unlock(&buf->lock);
|
|
|
|
tty_ldisc_deref(disc);
|
|
}
|
|
|
|
/**
|
|
* tty_flip_buffer_push - terminal
|
|
* @port: tty port to push
|
|
*
|
|
* Queue a push of the terminal flip buffers to the line discipline.
|
|
* Can be called from IRQ/atomic context.
|
|
*
|
|
* In the event of the queue being busy for flipping the work will be
|
|
* held off and retried later.
|
|
*/
|
|
|
|
void tty_flip_buffer_push(struct tty_port *port)
|
|
{
|
|
tty_schedule_flip(port);
|
|
}
|
|
EXPORT_SYMBOL(tty_flip_buffer_push);
|
|
|
|
/**
|
|
* tty_buffer_init - prepare a tty buffer structure
|
|
* @tty: tty to initialise
|
|
*
|
|
* Set up the initial state of the buffer management for a tty device.
|
|
* Must be called before the other tty buffer functions are used.
|
|
*/
|
|
|
|
void tty_buffer_init(struct tty_port *port)
|
|
{
|
|
struct tty_bufhead *buf = &port->buf;
|
|
|
|
mutex_init(&buf->lock);
|
|
tty_buffer_reset(&buf->sentinel, 0);
|
|
buf->head = &buf->sentinel;
|
|
buf->tail = &buf->sentinel;
|
|
init_llist_head(&buf->free);
|
|
atomic_set(&buf->mem_used, 0);
|
|
atomic_set(&buf->priority, 0);
|
|
INIT_WORK(&buf->work, flush_to_ldisc);
|
|
buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
|
|
}
|
|
|
|
/**
|
|
* tty_buffer_set_limit - change the tty buffer memory limit
|
|
* @port: tty port to change
|
|
*
|
|
* Change the tty buffer memory limit.
|
|
* Must be called before the other tty buffer functions are used.
|
|
*/
|
|
|
|
int tty_buffer_set_limit(struct tty_port *port, int limit)
|
|
{
|
|
if (limit < MIN_TTYB_SIZE)
|
|
return -EINVAL;
|
|
port->buf.mem_limit = limit;
|
|
return 0;
|
|
}
|
|
EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
|
|
|
|
/* slave ptys can claim nested buffer lock when handling BRK and INTR */
|
|
void tty_buffer_set_lock_subclass(struct tty_port *port)
|
|
{
|
|
lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
|
|
}
|
|
|
|
bool tty_buffer_restart_work(struct tty_port *port)
|
|
{
|
|
return queue_work(system_unbound_wq, &port->buf.work);
|
|
}
|
|
|
|
bool tty_buffer_cancel_work(struct tty_port *port)
|
|
{
|
|
return cancel_work_sync(&port->buf.work);
|
|
}
|
|
|
|
void tty_buffer_flush_work(struct tty_port *port)
|
|
{
|
|
flush_work(&port->buf.work);
|
|
}
|