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4bfe6cce13
In the copy_process() routine called by _do_fork(), failure to allocate
a PID (or further along in the function) will trigger an invocation to
exit_thread(). This is done to clean up from an earlier call to
copy_thread_tls(). Naturally, the child task is passed into exit_thread(),
however during the process, io_bitmap_exit() nullifies the parent's
io_bitmap rather than the child's.
As copy_thread_tls() has been called ahead of the failure, the reference
count on the calling thread's io_bitmap is incremented as we would expect.
However, io_bitmap_exit() doesn't accept any arguments, and thus assumes
it should trash the current thread's io_bitmap reference rather than the
child's. This is pretty sneaky in practice, because in all instances but
this one, exit_thread() is called with respect to the current task and
everything works out.
A determined attacker can issue an appropriate ioctl (i.e. KDENABIO) to
get a bitmap allocated, and force a clone3() syscall to fail by passing
in a zeroed clone_args structure. The kernel handles the erroneous struct
and the buggy code path is followed, and even though the parent's reference
to the io_bitmap is trashed, the child still holds a reference and thus
the structure will never be freed.
Fix this by tweaking io_bitmap_exit() and its subroutines to accept a
task_struct argument which to operate on.
Fixes: ea5f1cd7ab
("x86/ioperm: Remove bitmap if all permissions dropped")
Signed-off-by: Jay Lang <jaytlang@mit.edu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable#@vger.kernel.org
Link: https://lkml.kernel.org/r/20200524162742.253727-1-jaytlang@mit.edu
215 lines
5.3 KiB
C
215 lines
5.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* This contains the io-permission bitmap code - written by obz, with changes
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* by Linus. 32/64 bits code unification by Miguel Botón.
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*/
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#include <linux/capability.h>
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#include <linux/security.h>
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#include <linux/syscalls.h>
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#include <linux/bitmap.h>
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#include <linux/ioport.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <asm/io_bitmap.h>
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#include <asm/desc.h>
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#include <asm/syscalls.h>
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#ifdef CONFIG_X86_IOPL_IOPERM
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static atomic64_t io_bitmap_sequence;
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void io_bitmap_share(struct task_struct *tsk)
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{
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/* Can be NULL when current->thread.iopl_emul == 3 */
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if (current->thread.io_bitmap) {
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/*
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* Take a refcount on current's bitmap. It can be used by
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* both tasks as long as none of them changes the bitmap.
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*/
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refcount_inc(¤t->thread.io_bitmap->refcnt);
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tsk->thread.io_bitmap = current->thread.io_bitmap;
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}
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set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
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}
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static void task_update_io_bitmap(struct task_struct *tsk)
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{
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struct thread_struct *t = &tsk->thread;
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if (t->iopl_emul == 3 || t->io_bitmap) {
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/* TSS update is handled on exit to user space */
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set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
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} else {
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clear_tsk_thread_flag(tsk, TIF_IO_BITMAP);
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/* Invalidate TSS */
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preempt_disable();
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tss_update_io_bitmap();
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preempt_enable();
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}
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}
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void io_bitmap_exit(struct task_struct *tsk)
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{
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struct io_bitmap *iobm = tsk->thread.io_bitmap;
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tsk->thread.io_bitmap = NULL;
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task_update_io_bitmap(tsk);
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if (iobm && refcount_dec_and_test(&iobm->refcnt))
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kfree(iobm);
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}
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/*
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* This changes the io permissions bitmap in the current task.
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*/
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long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
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{
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struct thread_struct *t = ¤t->thread;
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unsigned int i, max_long;
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struct io_bitmap *iobm;
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if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
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return -EINVAL;
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if (turn_on && (!capable(CAP_SYS_RAWIO) ||
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security_locked_down(LOCKDOWN_IOPORT)))
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return -EPERM;
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/*
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* If it's the first ioperm() call in this thread's lifetime, set the
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* IO bitmap up. ioperm() is much less timing critical than clone(),
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* this is why we delay this operation until now:
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*/
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iobm = t->io_bitmap;
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if (!iobm) {
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/* No point to allocate a bitmap just to clear permissions */
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if (!turn_on)
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return 0;
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iobm = kmalloc(sizeof(*iobm), GFP_KERNEL);
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if (!iobm)
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return -ENOMEM;
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memset(iobm->bitmap, 0xff, sizeof(iobm->bitmap));
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refcount_set(&iobm->refcnt, 1);
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}
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/*
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* If the bitmap is not shared, then nothing can take a refcount as
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* current can obviously not fork at the same time. If it's shared
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* duplicate it and drop the refcount on the original one.
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*/
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if (refcount_read(&iobm->refcnt) > 1) {
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iobm = kmemdup(iobm, sizeof(*iobm), GFP_KERNEL);
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if (!iobm)
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return -ENOMEM;
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refcount_set(&iobm->refcnt, 1);
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io_bitmap_exit(current);
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}
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/*
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* Store the bitmap pointer (might be the same if the task already
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* head one). Must be done here so freeing the bitmap when all
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* permissions are dropped has the pointer set up.
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*/
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t->io_bitmap = iobm;
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/* Mark it active for context switching and exit to user mode */
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set_thread_flag(TIF_IO_BITMAP);
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/*
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* Update the tasks bitmap. The update of the TSS bitmap happens on
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* exit to user mode. So this needs no protection.
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*/
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if (turn_on)
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bitmap_clear(iobm->bitmap, from, num);
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else
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bitmap_set(iobm->bitmap, from, num);
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/*
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* Search for a (possibly new) maximum. This is simple and stupid,
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* to keep it obviously correct:
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*/
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max_long = UINT_MAX;
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for (i = 0; i < IO_BITMAP_LONGS; i++) {
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if (iobm->bitmap[i] != ~0UL)
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max_long = i;
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}
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/* All permissions dropped? */
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if (max_long == UINT_MAX) {
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io_bitmap_exit(current);
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return 0;
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}
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iobm->max = (max_long + 1) * sizeof(unsigned long);
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/*
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* Update the sequence number to force a TSS update on return to
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* user mode.
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*/
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iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence);
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return 0;
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}
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SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
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{
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return ksys_ioperm(from, num, turn_on);
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}
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/*
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* The sys_iopl functionality depends on the level argument, which if
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* granted for the task is used to enable access to all 65536 I/O ports.
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*
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* This does not use the IOPL mechanism provided by the CPU as that would
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* also allow the user space task to use the CLI/STI instructions.
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*
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* Disabling interrupts in a user space task is dangerous as it might lock
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* up the machine and the semantics vs. syscalls and exceptions is
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* undefined.
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*
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* Setting IOPL to level 0-2 is disabling I/O permissions. Level 3
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* 3 enables them.
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*
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* IOPL is strictly per thread and inherited on fork.
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*/
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SYSCALL_DEFINE1(iopl, unsigned int, level)
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{
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struct thread_struct *t = ¤t->thread;
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unsigned int old;
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if (level > 3)
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return -EINVAL;
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old = t->iopl_emul;
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/* No point in going further if nothing changes */
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if (level == old)
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return 0;
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/* Trying to gain more privileges? */
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if (level > old) {
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if (!capable(CAP_SYS_RAWIO) ||
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security_locked_down(LOCKDOWN_IOPORT))
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return -EPERM;
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}
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t->iopl_emul = level;
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task_update_io_bitmap(current);
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return 0;
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}
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#else /* CONFIG_X86_IOPL_IOPERM */
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long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
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{
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return -ENOSYS;
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}
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SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
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{
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return -ENOSYS;
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}
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SYSCALL_DEFINE1(iopl, unsigned int, level)
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{
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return -ENOSYS;
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}
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#endif
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