[PATCH] cifs: Fix cached_fid refcnt leak in open_shroot

[PATCH] cifs: Fix cached_fid refcnt leak in open_shroot

[Xiyu Yang]

open_shroot() invokes kref_get(), which increases the refcount of the
"tcon->crfid" object. When open_shroot() returns not zero, it means the
open operation failed and close_shroot() will not be called to decrement
the refcount of the "tcon->crfid".

The reference counting issue happens in one normal path of
open_shroot(). When the cached root have been opened successfully in a
concurrent process, the function increases the refcount and jump to
"oshr_free" to return. However the current return value "rc" may not
equal to 0, thus the increased refcount will not be balanced outside the
function, causing a refcnt leak.

Fix this issue by setting the value of "rc" to 0 before jumping to
"oshr_free" label.

Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
---
 fs/cifs/smb2ops.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 736d86b8a910..28553d45604e 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -763,6 +763,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon,
 			/* close extra handle outside of crit sec */
 			SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
 		}
+		rc = 0;
 		goto oshr_free;
 	}
 
-- 
2.7.4

Re: [PATCH] cifs: Fix cached_fid refcnt leak in open_shroot

[Steve French]

added cc:stable and merged into cifs-2.6.git for-next

On Sat, Jun 13, 2020 at 7:36 AM Xiyu Yang <xiyuyang19@fudan.edu.cn> wrote:
>
> open_shroot() invokes kref_get(), which increases the refcount of the
> "tcon->crfid" object. When open_shroot() returns not zero, it means the
> open operation failed and close_shroot() will not be called to decrement
> the refcount of the "tcon->crfid".
>
> The reference counting issue happens in one normal path of
> open_shroot(). When the cached root have been opened successfully in a
> concurrent process, the function increases the refcount and jump to
> "oshr_free" to return. However the current return value "rc" may not
> equal to 0, thus the increased refcount will not be balanced outside the
> function, causing a refcnt leak.
>
> Fix this issue by setting the value of "rc" to 0 before jumping to
> "oshr_free" label.
>
> Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
> ---
>  fs/cifs/smb2ops.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index 736d86b8a910..28553d45604e 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -763,6 +763,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon,
>                         /* close extra handle outside of crit sec */
>                         SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
>                 }
> +               rc = 0;
>                 goto oshr_free;
>         }
>
> --
> 2.7.4
>


-- 
Thanks,

Steve