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| author | Andrii Nakryiko <andrii@kernel.org> | 2020-10-14 13:45:28 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-10-14 14:54:45 -0700 |
| commit | 09cad07547445bf3a41683e4d3abcd154c123ef5 (patch) | |
| tree | 87c5446a685d3ab5db6e91d869a6726960e892b3 | |
| parent | 4da9af0014b51c8b015ed8c622440ef28912efe6 (diff) | |
| download | linux-09cad07547445bf3a41683e4d3abcd154c123ef5.tar.bz2 | |
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: f2683bd8d5bd ("[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>
| -rw-r--r-- | fs/d_path.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/fs/d_path.c b/fs/d_path.c index 0f1fc1743302..a69e2cd36e6e 100644 --- a/fs/d_path.c +++ b/fs/d_path.c @@ -102,6 +102,8 @@ restart: if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) { struct mount *parent = READ_ONCE(mnt->mnt_parent); + struct mnt_namespace *mnt_ns; + /* Escaped? */ if (dentry != vfsmnt->mnt_root) { bptr = *buffer; @@ -116,7 +118,9 @@ restart: vfsmnt = &mnt->mnt; continue; } - if (is_mounted(vfsmnt) && !is_anon_ns(mnt->mnt_ns)) + mnt_ns = READ_ONCE(mnt->mnt_ns); + /* open-coded is_mounted() to use local mnt_ns */ + if (!IS_ERR_OR_NULL(mnt_ns) && !is_anon_ns(mnt_ns)) error = 1; // absolute root else error = 2; // detached or not attached yet |