]> git.baikalelectronics.ru Git - kernel.git/commit
fs: fix NULL dereference due to data race in prepend_path()
authorAndrii Nakryiko <andrii@kernel.org>
Wed, 14 Oct 2020 20:45:28 +0000 (13:45 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 14 Oct 2020 21:54:45 +0000 (14:54 -0700)
commit444da20c393eb030718ecc111e22315db63d15b4
tree87c5446a685d3ab5db6e91d869a6726960e892b3
parentf2a232aa89d62ef6d90007909dc74fb0880b673f
fs: fix NULL dereference due to data race in prepend_path()

Fix data race in prepend_path() with re-reading mnt->mnt_ns twice
without holding the lock.

is_mounted() does check for NULL, but is_anon_ns(mnt->mnt_ns) might
re-read the pointer again which could be NULL already, if in between
reads one of kern_unmount()/kern_unmount_array()/umount_tree() sets
mnt->mnt_ns to NULL.

This is seen in production with the following stack trace:

  BUG: kernel NULL pointer dereference, address: 0000000000000048
  ...
  RIP: 0010:prepend_path.isra.4+0x1ce/0x2e0
  Call Trace:
    d_path+0xe6/0x150
    proc_pid_readlink+0x8f/0x100
    vfs_readlink+0xf8/0x110
    do_readlinkat+0xfd/0x120
    __x64_sys_readlinkat+0x1a/0x20
    do_syscall_64+0x42/0x110
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 53837707b3d2 ("[PATCH] fix d_absolute_path() interplay with fsmount()")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
fs/d_path.c