nfsd4: fix bad pointer on failure to find delegation

In case of a nonempty list, the return on error here is obviously bogus;
it ends up being a pointer to the list head instead of to any valid
delegation on the list.

In particular, if nfsd4_delegreturn() hits this case, and you're quite unlucky,
then renew_client may oops, and it may take an embarassingly long time to
figure out why.  Facepalm.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000090
IP: [<ffffffff81292965>] nfsd4_delegreturn+0x125/0x200
...

Cc: stable@kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 54b60bfceb8d0c6b8d4ec5100a2aedb6600a1d5d..7b566ec14e1833cac3f7c61d5ab6b5bb169e3abb 100644 (file)
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -2445,15 +2445,16 @@ nfs4_check_delegmode(struct nfs4_delegation *dp, int flags)
 static struct nfs4_delegation *
 find_delegation_file(struct nfs4_file *fp, stateid_t *stid)
 {
-       struct nfs4_delegation *dp = NULL;
+       struct nfs4_delegation *dp;
 
        spin_lock(&recall_lock);
-       list_for_each_entry(dp, &fp->fi_delegations, dl_perfile) {
-               if (dp->dl_stateid.si_stateownerid == stid->si_stateownerid)
-                       break;
-       }
+       list_for_each_entry(dp, &fp->fi_delegations, dl_perfile)
+               if (dp->dl_stateid.si_stateownerid == stid->si_stateownerid) {
+                       spin_unlock(&recall_lock);
+                       return dp;
+               }
        spin_unlock(&recall_lock);
-       return dp;
+       return NULL;
 }
 
 int share_access_to_flags(u32 share_access)