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nfsd: fix use-after-free due to delegation race

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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>
This commit is contained in:
J. Bruce Fields 2021-11-29 15:08:00 -05:00
parent b10252c7ae
commit 548ec0805c
1 changed files with 7 additions and 2 deletions
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9
fs/nfsd/nfs4state.c
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@ -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);
}