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ovl: fix null pointer dereference in ovl_get_acl_rcu()

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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].

Use the helper ovl_i_path_realinode() to get realinode and then do
non-nullptr checking.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=217404
Fixes: 332f606b32 ("ovl: enable RCU'd ->get_acl()")
Cc: <stable@vger.kernel.org> # v5.15
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Suggested-by: Christian Brauner <brauner@kernel.org>
Suggested-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Zhihao Cheng 2023-05-16 22:16:19 +08:00 committed by Amir Goldstein
parent 1a73f5b8f0
commit f4e19e595c
1 changed files with 6 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
fs/overlayfs/inode.c
View File

@ -558,20 +558,20 @@ struct posix_acl *do_ovl_get_acl(struct mnt_idmap *idmap,
struct inode *inode, int type,
bool rcu, bool noperm)
{
struct inode *realinode = ovl_inode_real(inode);
struct inode *realinode;
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) {
realinode = ovl_i_path_real(inode, &realpath);
if (!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