Re: [PATCH 5.15] ovl: fix null pointer dereference in ovl_get_acl_rcu()

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在 2023/7/17 2:26, Amir Goldstein 写道:
On Mon, Jul 10, 2023 at 6:29 AM Zhihao Cheng <chengzhihao1@xxxxxxxxxx> wrote:

[ Upstream commit f4e19e595cc2e76a8a58413eb19d3d9c51328b53 ]

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.

There are some changes from upstream commit:
1. Corrusponds to do_ovl_get_acl() in 5.15 is ovl_get_acl()
2. ovl_i_path_real is not imported in 5.15, we can get realinode by
    ovl_inode_real
3. CONFIG_FS_POSIX_ACL checking is dropped in commit
    ded536561a3674327dfa4bb389085705cae22b8a ("ovl: improve ovl_get_acl()
    if POSIX ACL support is off"), we still keep it in 5.15.

Zhihao,

Can you please provide also the backport for 6.1.


Sure, I sent it out, please refer to https://lore.kernel.org/stable/20230717030904.1669754-1-chengzhihao1@xxxxxxxxxx/T/#t.

Basically, the same as this one without the CONFIG_FS_POSIX_ACL check.

Thanks,
Amir.


Link: https://bugzilla.kernel.org/show_bug.cgi?id=217404
Fixes: 332f606b32b6 ("ovl: enable RCU'd ->get_acl()")
Cc: <stable@xxxxxxxxxxxxxxx> # v5.15
Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
Suggested-by: Christian Brauner <brauner@xxxxxxxxxx>
Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx>
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
---
  fs/overlayfs/inode.c | 10 +++++++++-
  1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index d41f0c8e0e2a..65e5e6eb761a 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -453,7 +453,15 @@ struct posix_acl *ovl_get_acl(struct inode *inode, int type, bool rcu)
         const struct cred *old_cred;
         struct posix_acl *acl;

-       if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
+       if (!IS_ENABLED(CONFIG_FS_POSIX_ACL))
+               return NULL;
+
+       if (!realinode) {
+               WARN_ON(!rcu);
+               return ERR_PTR(-ECHILD);
+       }
+
+       if (!IS_POSIXACL(realinode))
                 return NULL;

         if (rcu)
--
2.39.2

.





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