On Fri, Sep 20, 2019 at 02:23:00PM -0700, Pavel Shilovsky wrote:

Fri, Sep 20, 2019 at 14:08, Pavel Shilovsky piastryyy@gmail.com:

...

From: Aurelien Aptel aaptel@suse.com

Commit 7e5a70ad88b1 ("CIFS: fix deadlock in cached root handling") upstream.

Prevent deadlock between open_shroot() and cifs_mark_open_files_invalid() by releasing the lock before entering SMB2_open, taking it again after and checking if we still need to use the result.

CC: stable@vger.kernel.org # v4.19+ Link: https://lore.kernel.org/linux-cifs/684ed01c-cbca-2716-bc28-b0a59a0f8521@prod... Fixes: 3d4ef9a15343 ("smb3: fix redundant opens on root") Signed-off-by: Aurelien Aptel aaptel@suse.com Signed-off-by: Pavel Shilovsky pshilov@microsoft.com

---

fs/cifs/smb2ops.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c index cc9e846a3865..094be406cde4 100644 --- a/fs/cifs/smb2ops.c +++ b/fs/cifs/smb2ops.c @@ -553,7 +553,50 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid) oparams.fid = pfid; oparams.reconnect = false;

•   /*
  

•    * We do not hold the lock for the open because in case
  

•    * SMB2_open needs to reconnect, it will end up calling
  

•    * cifs_mark_open_files_invalid() which takes the lock again
  

•    * thus causing a deadlock
  

•    */
  

•   mutex_unlock(&tcon->crfid.fid_mutex);
    rc = SMB2_open(xid, &oparams, &srch_path, &oplock, NULL, NULL, NULL);
  

•   mutex_lock(&tcon->crfid.fid_mutex);
  

•   /*
  

•    * Now we need to check again as the cached root might have
  

•    * been successfully re-opened from a concurrent process
  

•    */
  

•   if (tcon->crfid.is_valid) {
  

•           /* work was already done */
  

•           /* stash fids for close() later */
  

•           struct cifs_fid fid = {
  

•                   .persistent_fid = pfid->persistent_fid,
  

•                   .volatile_fid = pfid->volatile_fid,
  

•           };
  

•           /*
  

•            * Caller expects this func to set pfid to a valid
  

•            * cached root, so we copy the existing one and get a
  

•            * reference
  

•            */
  

•           memcpy(pfid, tcon->crfid.fid, sizeof(*pfid));
  

•           kref_get(&tcon->crfid.refcount);
  

•           mutex_unlock(&tcon->crfid.fid_mutex);
  

•           if (rc == 0) {
  

•                   /* close extra handle outside of critical section */
  

•                   SMB2_close(xid, tcon, fid.persistent_fid,
  

•                              fid.volatile_fid);
  

•           }
  

•           return 0;
  

•   }
  

•   /* Cached root is still invalid, continue normaly */
  

•   if (rc == 0) {
            memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
            tcon->crfid.tcon = tcon;
  

@@ -561,6 +604,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid) kref_init(&tcon->crfid.refcount); kref_get(&tcon->crfid.refcount); }

•   mutex_unlock(&tcon->crfid.fid_mutex);
    return rc;
  

}

2.17.1

Forgot to mention that kernels 5.1.y and above already have the appropriate patch. This is a backport for 4.19.

Now queued up, thanks!

greg k-h