linux-stable/fs/jffs2
Jamie Iles a61df3c413 jffs2: Fix NULL pointer dereference in rp_size fs option parsing
syzkaller found the following JFFS2 splat:

  Unable to handle kernel paging request at virtual address dfffa00000000001
  Mem abort info:
    ESR = 0x96000004
    EC = 0x25: DABT (current EL), IL = 32 bits
    SET = 0, FnV = 0
    EA = 0, S1PTW = 0
  Data abort info:
    ISV = 0, ISS = 0x00000004
    CM = 0, WnR = 0
  [dfffa00000000001] address between user and kernel address ranges
  Internal error: Oops: 96000004 [#1] SMP
  Dumping ftrace buffer:
     (ftrace buffer empty)
  Modules linked in:
  CPU: 0 PID: 12745 Comm: syz-executor.5 Tainted: G S                5.9.0-rc8+ #98
  Hardware name: linux,dummy-virt (DT)
  pstate: 20400005 (nzCv daif +PAN -UAO BTYPE=--)
  pc : jffs2_parse_param+0x138/0x308 fs/jffs2/super.c:206
  lr : jffs2_parse_param+0x108/0x308 fs/jffs2/super.c:205
  sp : ffff000022a57910
  x29: ffff000022a57910 x28: 0000000000000000
  x27: ffff000057634008 x26: 000000000000d800
  x25: 000000000000d800 x24: ffff0000271a9000
  x23: ffffa0001adb5dc0 x22: ffff000023fdcf00
  x21: 1fffe0000454af2c x20: ffff000024cc9400
  x19: 0000000000000000 x18: 0000000000000000
  x17: 0000000000000000 x16: ffffa000102dbdd0
  x15: 0000000000000000 x14: ffffa000109e44bc
  x13: ffffa00010a3a26c x12: ffff80000476e0b3
  x11: 1fffe0000476e0b2 x10: ffff80000476e0b2
  x9 : ffffa00010a3ad60 x8 : ffff000023b70593
  x7 : 0000000000000003 x6 : 00000000f1f1f1f1
  x5 : ffff000023fdcf00 x4 : 0000000000000002
  x3 : ffffa00010000000 x2 : 0000000000000001
  x1 : dfffa00000000000 x0 : 0000000000000008
  Call trace:
   jffs2_parse_param+0x138/0x308 fs/jffs2/super.c:206
   vfs_parse_fs_param+0x234/0x4e8 fs/fs_context.c:117
   vfs_parse_fs_string+0xe8/0x148 fs/fs_context.c:161
   generic_parse_monolithic+0x17c/0x208 fs/fs_context.c:201
   parse_monolithic_mount_data+0x7c/0xa8 fs/fs_context.c:649
   do_new_mount fs/namespace.c:2871 [inline]
   path_mount+0x548/0x1da8 fs/namespace.c:3192
   do_mount+0x124/0x138 fs/namespace.c:3205
   __do_sys_mount fs/namespace.c:3413 [inline]
   __se_sys_mount fs/namespace.c:3390 [inline]
   __arm64_sys_mount+0x164/0x238 fs/namespace.c:3390
   __invoke_syscall arch/arm64/kernel/syscall.c:36 [inline]
   invoke_syscall arch/arm64/kernel/syscall.c:48 [inline]
   el0_svc_common.constprop.0+0x15c/0x598 arch/arm64/kernel/syscall.c:149
   do_el0_svc+0x60/0x150 arch/arm64/kernel/syscall.c:195
   el0_svc+0x34/0xb0 arch/arm64/kernel/entry-common.c:226
   el0_sync_handler+0xc8/0x5b4 arch/arm64/kernel/entry-common.c:236
   el0_sync+0x15c/0x180 arch/arm64/kernel/entry.S:663
  Code: d2d40001 f2fbffe1 91002260 d343fc02 (38e16841)
  ---[ end trace 4edf690313deda44 ]---

This is because since ec10a24f10, the option parsing happens before
fill_super and so the MTD device isn't associated with the filesystem.
Defer the size check until there is a valid association.

Fixes: ec10a24f10 ("vfs: Convert jffs2 to use the new mount API")
Cc: <stable@vger.kernel.org>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Jamie Iles <jamie@nuviainc.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
2020-12-13 21:57:21 +01:00
..
acl.c Convert jffs2 acl to struct_size 2018-06-12 16:19:22 -07:00
acl.h Convert jffs2 acl to struct_size 2018-06-12 16:19:22 -07:00
background.c signal: Remove the siginfo paramater from kernel_dqueue_signal 2018-09-11 21:19:14 +02:00
build.c
compr.c
compr.h
compr_lzo.c
compr_rtime.c
compr_rubin.c
compr_zlib.c
debug.c
debug.h jffs2: Fix if/else empty body warnings 2020-12-13 21:51:54 +01:00
dir.c jffs2: fix UAF problem 2020-08-02 23:56:13 +02:00
erase.c treewide: Remove uninitialized_var() usage 2020-07-16 12:35:15 -07:00
file.c jffs2: pass the correct prototype to read_cache_page 2019-07-12 11:05:43 -07:00
fs.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
gc.c jffs2: Remove jffs2_gc_fetch_page and jffs2_gc_release_page 2019-09-15 22:42:33 +02:00
ioctl.c
jffs2_fs_i.h
jffs2_fs_sb.h jffs2: Allow setting rp_size to zero during remounting 2020-12-13 21:56:24 +01:00
Kconfig treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
LICENCE
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
malloc.c
nodelist.c Revert "jffs2: Fix possible null-pointer dereferences in jffs2_add_frag_to_fragtree()" 2019-11-29 11:29:58 +01:00
nodelist.h jffs2: remove trailing semicolon in macro definition 2020-12-13 21:57:20 +01:00
nodemgmt.c sched/headers: Prepare to move signal wakeup & sigpending methods from <linux/sched.h> into <linux/sched/signal.h> 2017-03-02 08:42:32 +01:00
os-linux.h This pull request contains the following changes for UBI, UBIFS and JFFS2: 2019-09-21 11:10:16 -07:00
read.c
readinode.c jffs2: Fix GC exit abnormally 2020-12-13 21:55:39 +01:00
README.Locking
scan.c jffs2: fix jffs2 mounting failure 2020-08-02 23:56:13 +02:00
security.c switch xattr_handler->set() to passing dentry and inode separately 2016-05-27 15:39:43 -04:00
summary.c vfs: make the string hashes salt the hash 2016-06-10 20:21:46 -07:00
summary.h jffs2: Replace zero-length array with flexible-array 2020-06-15 23:08:31 -05:00
super.c jffs2: Fix NULL pointer dereference in rp_size fs option parsing 2020-12-13 21:57:21 +01:00
symlink.c vfs: remove ".readlink = generic_readlink" assignments 2016-12-09 16:45:04 +01:00
TODO
wbuf.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
write.c vfs: make the string hashes salt the hash 2016-06-10 20:21:46 -07:00
writev.c
xattr.c
xattr.h jffs2: Remove jffs2_{get,set,remove}xattr macros 2016-10-06 22:17:38 -04:00
xattr_trusted.c switch xattr_handler->set() to passing dentry and inode separately 2016-05-27 15:39:43 -04:00
xattr_user.c switch xattr_handler->set() to passing dentry and inode separately 2016-05-27 15:39:43 -04:00

	JFFS2 LOCKING DOCUMENTATION
	---------------------------

This document attempts to describe the existing locking rules for
JFFS2. It is not expected to remain perfectly up to date, but ought to
be fairly close.


	alloc_sem
	---------

The alloc_sem is a per-filesystem mutex, used primarily to ensure
contiguous allocation of space on the medium. It is automatically
obtained during space allocations (jffs2_reserve_space()) and freed
upon write completion (jffs2_complete_reservation()). Note that
the garbage collector will obtain this right at the beginning of
jffs2_garbage_collect_pass() and release it at the end, thereby
preventing any other write activity on the file system during a
garbage collect pass.

When writing new nodes, the alloc_sem must be held until the new nodes
have been properly linked into the data structures for the inode to
which they belong. This is for the benefit of NAND flash - adding new
nodes to an inode may obsolete old ones, and by holding the alloc_sem
until this happens we ensure that any data in the write-buffer at the
time this happens are part of the new node, not just something that
was written afterwards. Hence, we can ensure the newly-obsoleted nodes
don't actually get erased until the write-buffer has been flushed to
the medium.

With the introduction of NAND flash support and the write-buffer, 
the alloc_sem is also used to protect the wbuf-related members of the
jffs2_sb_info structure. Atomically reading the wbuf_len member to see
if the wbuf is currently holding any data is permitted, though.

Ordering constraints: See f->sem.


	File Mutex f->sem
	---------------------

This is the JFFS2-internal equivalent of the inode mutex i->i_sem.
It protects the contents of the jffs2_inode_info private inode data,
including the linked list of node fragments (but see the notes below on
erase_completion_lock), etc.

The reason that the i_sem itself isn't used for this purpose is to
avoid deadlocks with garbage collection -- the VFS will lock the i_sem
before calling a function which may need to allocate space. The
allocation may trigger garbage-collection, which may need to move a
node belonging to the inode which was locked in the first place by the
VFS. If the garbage collection code were to attempt to lock the i_sem
of the inode from which it's garbage-collecting a physical node, this
lead to deadlock, unless we played games with unlocking the i_sem
before calling the space allocation functions.

Instead of playing such games, we just have an extra internal
mutex, which is obtained by the garbage collection code and also
by the normal file system code _after_ allocation of space.

Ordering constraints: 

	1. Never attempt to allocate space or lock alloc_sem with 
	   any f->sem held.
	2. Never attempt to lock two file mutexes in one thread.
	   No ordering rules have been made for doing so.
	3. Never lock a page cache page with f->sem held.


	erase_completion_lock spinlock
	------------------------------

This is used to serialise access to the eraseblock lists, to the
per-eraseblock lists of physical jffs2_raw_node_ref structures, and
(NB) the per-inode list of physical nodes. The latter is a special
case - see below.

As the MTD API no longer permits erase-completion callback functions
to be called from bottom-half (timer) context (on the basis that nobody
ever actually implemented such a thing), it's now sufficient to use
a simple spin_lock() rather than spin_lock_bh().

Note that the per-inode list of physical nodes (f->nodes) is a special
case. Any changes to _valid_ nodes (i.e. ->flash_offset & 1 == 0) in
the list are protected by the file mutex f->sem. But the erase code
may remove _obsolete_ nodes from the list while holding only the
erase_completion_lock. So you can walk the list only while holding the
erase_completion_lock, and can drop the lock temporarily mid-walk as
long as the pointer you're holding is to a _valid_ node, not an
obsolete one.

The erase_completion_lock is also used to protect the c->gc_task
pointer when the garbage collection thread exits. The code to kill the
GC thread locks it, sends the signal, then unlocks it - while the GC
thread itself locks it, zeroes c->gc_task, then unlocks on the exit path.


	inocache_lock spinlock
	----------------------

This spinlock protects the hashed list (c->inocache_list) of the
in-core jffs2_inode_cache objects (each inode in JFFS2 has the
correspondent jffs2_inode_cache object). So, the inocache_lock
has to be locked while walking the c->inocache_list hash buckets.

This spinlock also covers allocation of new inode numbers, which is
currently just '++->highest_ino++', but might one day get more complicated
if we need to deal with wrapping after 4 milliard inode numbers are used.

Note, the f->sem guarantees that the correspondent jffs2_inode_cache
will not be removed. So, it is allowed to access it without locking
the inocache_lock spinlock. 

Ordering constraints: 

	If both erase_completion_lock and inocache_lock are needed, the
	c->erase_completion has to be acquired first.


	erase_free_sem
	--------------

This mutex is only used by the erase code which frees obsolete node
references and the jffs2_garbage_collect_deletion_dirent() function.
The latter function on NAND flash must read _obsolete_ nodes to
determine whether the 'deletion dirent' under consideration can be
discarded or whether it is still required to show that an inode has
been unlinked. Because reading from the flash may sleep, the
erase_completion_lock cannot be held, so an alternative, more
heavyweight lock was required to prevent the erase code from freeing
the jffs2_raw_node_ref structures in question while the garbage
collection code is looking at them.

Suggestions for alternative solutions to this problem would be welcomed.


	wbuf_sem
	--------

This read/write semaphore protects against concurrent access to the
write-behind buffer ('wbuf') used for flash chips where we must write
in blocks. It protects both the contents of the wbuf and the metadata
which indicates which flash region (if any) is currently covered by 
the buffer.

Ordering constraints:
	Lock wbuf_sem last, after the alloc_sem or and f->sem.


	c->xattr_sem
	------------

This read/write semaphore protects against concurrent access to the
xattr related objects which include stuff in superblock and ic->xref.
In read-only path, write-semaphore is too much exclusion. It's enough
by read-semaphore. But you must hold write-semaphore when updating,
creating or deleting any xattr related object.

Once xattr_sem released, there would be no assurance for the existence
of those objects. Thus, a series of processes is often required to retry,
when updating such a object is necessary under holding read semaphore.
For example, do_jffs2_getxattr() holds read-semaphore to scan xref and
xdatum at first. But it retries this process with holding write-semaphore
after release read-semaphore, if it's necessary to load name/value pair
from medium.

Ordering constraints:
	Lock xattr_sem last, after the alloc_sem.