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authorJ. Bruce Fields <bfields@redhat.com>2021-11-29 15:08:00 -0500
committerJ. Bruce Fields <bfields@redhat.com>2021-12-10 11:55:15 -0500
commit548ec0805c399c65ed66c6641be467f717833ab5 (patch)
treef8c3f64767ecff4aa77f22157f38465a9e333f26
parentb10252c7ae9c9d7c90552f88b544a44ee773af64 (diff)
nfsd: fix use-after-free due to delegation race
A delegation break could arrive as soon as we've called vfs_setlease. A delegation break runs a callback which immediately (in nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we then exit nfs4_set_delegation without hashing the delegation, it will be freed as soon as the callback is done with it, without ever being removed from del_recall_lru. Symptoms show up later as use-after-free or list corruption warnings, usually in the laundromat thread. I suspect aba2072f4523 "nfsd: grant read delegations to clients holding writes" made this bug easier to hit, but I looked as far back as v3.0 and it looks to me it already had the same problem. So I'm not sure where the bug was introduced; it may have been there from the beginning. Cc: stable@vger.kernel.org Signed-off-by: J. Bruce Fields <bfields@redhat.com>
-rw-r--r--fs/nfsd/nfs4state.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index bfad94c70b84..1956d377d1a6 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1207,6 +1207,11 @@ hash_delegation_locked(struct nfs4_delegation *dp, struct nfs4_file *fp)
return 0;
}
+static bool delegation_hashed(struct nfs4_delegation *dp)
+{
+ return !(list_empty(&dp->dl_perfile));
+}
+
static bool
unhash_delegation_locked(struct nfs4_delegation *dp)
{
@@ -1214,7 +1219,7 @@ unhash_delegation_locked(struct nfs4_delegation *dp)
lockdep_assert_held(&state_lock);
- if (list_empty(&dp->dl_perfile))
+ if (!delegation_hashed(dp))
return false;
dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID;
@@ -4598,7 +4603,7 @@ static void nfsd4_cb_recall_prepare(struct nfsd4_callback *cb)
* queued for a lease break. Don't queue it again.
*/
spin_lock(&state_lock);
- if (dp->dl_time == 0) {
+ if (delegation_hashed(dp) && dp->dl_time == 0) {
dp->dl_time = ktime_get_boottime_seconds();
list_add_tail(&dp->dl_recall_lru, &nn->del_recall_lru);
}