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authorAndrii Nakryiko <andrii@kernel.org>2020-10-14 13:45:28 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-10-14 14:54:45 -0700
commit09cad07547445bf3a41683e4d3abcd154c123ef5 (patch)
tree87c5446a685d3ab5db6e91d869a6726960e892b3 /fs
parent4da9af0014b51c8b015ed8c622440ef28912efe6 (diff)
downloadlinux-stericsson-09cad07547445bf3a41683e4d3abcd154c123ef5.tar.gz
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>
Diffstat (limited to 'fs')
-rw-r--r--fs/d_path.c6
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