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

[Zhihao Cheng <chengzhihao1@huawei.com>]

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