Following process:
P1 P2
path_openat
link_path_walk
may_lookup
inode_permission(rcu)
ovl_permission
acl_permission_check
check_acl
get_cached_acl_rcu
ovl_get_inode_acl
realinode = ovl_inode_real(ovl_inode)
drop_cache
__dentry_kill(ovl_dentry)
iput(ovl_inode)
ovl_destroy_inode(ovl_inode)
dput(oi->__upperdentry)
dentry_kill(upperdentry)
dentry_unlink_inode
upperdentry->d_inode = NULL
ovl_inode_upper
upperdentry = ovl_i_dentry_upper(ovl_inode)
d_inode(upperdentry) // returns NULL
IS_POSIXACL(realinode) // NULL pointer dereference
, will trigger an null pointer dereference at realinode:
[ 205.472797] BUG: kernel NULL pointer dereference, address:
0000000000000028
[ 205.476701] CPU: 2 PID: 2713 Comm: ls Not tainted
6.3.0-12064-g2edfa098e750-dirty #1216
[ 205.478754] RIP: 0010:do_ovl_get_acl+0x5d/0x300
[ 205.489584] Call Trace:
[ 205.489812] <TASK>
[ 205.490014] ovl_get_inode_acl+0x26/0x30
[ 205.490466] get_cached_acl_rcu+0x61/0xa0
[ 205.490908] generic_permission+0x1bf/0x4e0
[ 205.491447] ovl_permission+0x79/0x1b0
[ 205.491917] inode_permission+0x15e/0x2c0
[ 205.492425] link_path_walk+0x115/0x550
[ 205.493311] path_lookupat.isra.0+0xb2/0x200
[ 205.493803] filename_lookup+0xda/0x240
[ 205.495747] vfs_fstatat+0x7b/0xb0
Fetch a reproducer in [Link].
Fix it by checking realinode whether to be NULL before accessing it.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217404
Fixes: 332f606b32b6 ("ovl: enable RCU'd ->get_acl()")
Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
---
fs/overlayfs/inode.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 541cf3717fc2..38cfdf9e2b44 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -563,16 +563,16 @@ struct posix_acl *do_ovl_get_acl(struct mnt_idmap *idmap,
struct posix_acl *acl;
struct path realpath;
- if (!IS_POSIXACL(realinode))
- return NULL;
-
/* Careful in RCU walk mode */
ovl_i_path_real(inode, &realpath);
- if (!realpath.dentry) {
+ if (!realpath.dentry || !realinode) {
WARN_ON(!rcu);
return ERR_PTR(-ECHILD);
}
+ if (!IS_POSIXACL(realinode))
+ return NULL;
+
if (rcu) {
/*
* If the layer is idmapped drop out of RCU path walk
--
2.31.1
