On Wed, 2009-11-18 at 11:56 +1100, Neil Brown wrote: > Hi again Trond, > > I've been looking at a customer report of an oops in > rpcauth_lookup_credcache. > https://bugzilla.novell.com/show_bug.cgi?id=547137 > > It appears that one of the hash chains in the cache has become > corrupted. How about the following patch? Cheers Trond -------------------------------------------------------------------------- RPC: Fix two potential races in put_rpccred From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx> It is possible for rpcauth_destroy_credcache() to cause the rpc credentials to be unhashed while put_rpccred is waiting for the rpc_credcache_lock on another cpu. Should this happen, then we can end up calling hlist_del_rcu(&cred->cr_hash) a second time, thus causing list corruption. Should the credential actually be hashed, it is possible for rpcauth_lookup_credcache to find and reference it before we get round to unhashing it. We should therefore check for whether the credential is referenced after we've unhashed it. See https://bugzilla.novell.com/show_bug.cgi?id=547137 Reported-by: Neil Brown <neilb@xxxxxxx> Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx> --- net/sunrpc/auth.c | 39 +++++++++++++++++++++++---------------- 1 files changed, 23 insertions(+), 16 deletions(-) diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c index 54a4e04..7ee6f7e 100644 --- a/net/sunrpc/auth.c +++ b/net/sunrpc/auth.c @@ -123,16 +123,19 @@ rpcauth_unhash_cred_locked(struct rpc_cred *cred) clear_bit(RPCAUTH_CRED_HASHED, &cred->cr_flags); } -static void +static int rpcauth_unhash_cred(struct rpc_cred *cred) { spinlock_t *cache_lock; + int ret; cache_lock = &cred->cr_auth->au_credcache->lock; spin_lock(cache_lock); - if (atomic_read(&cred->cr_count) == 0) + ret = atomic_read(&cred->cr_count) == 0; + if (ret) rpcauth_unhash_cred_locked(cred); spin_unlock(cache_lock); + return ret; } /* @@ -446,31 +449,35 @@ void put_rpccred(struct rpc_cred *cred) { /* Fast path for unhashed credentials */ - if (test_bit(RPCAUTH_CRED_HASHED, &cred->cr_flags) != 0) - goto need_lock; - - if (!atomic_dec_and_test(&cred->cr_count)) + if (test_bit(RPCAUTH_CRED_HASHED, &cred->cr_flags) == 0) { + if (atomic_dec_and_test(&cred->cr_count)) + cred->cr_ops->crdestroy(cred); return; - goto out_destroy; -need_lock: + } + if (!atomic_dec_and_lock(&cred->cr_count, &rpc_credcache_lock)) return; if (!list_empty(&cred->cr_lru)) { number_cred_unused--; list_del_init(&cred->cr_lru); } - if (test_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags) == 0) - rpcauth_unhash_cred(cred); if (test_bit(RPCAUTH_CRED_HASHED, &cred->cr_flags) != 0) { - cred->cr_expire = jiffies; - list_add_tail(&cred->cr_lru, &cred_unused); - number_cred_unused++; - spin_unlock(&rpc_credcache_lock); - return; + if (test_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags) != 0) { + cred->cr_expire = jiffies; + list_add_tail(&cred->cr_lru, &cred_unused); + number_cred_unused++; + goto out_nodestroy; + } + if (!rpcauth_unhash_cred(cred)) { + /* We were hashed and someone looked us up... */ + goto out_nodestroy; + } } spin_unlock(&rpc_credcache_lock); -out_destroy: cred->cr_ops->crdestroy(cred); + return; +out_nodestroy: + spin_unlock(&rpc_credcache_lock); } EXPORT_SYMBOL_GPL(put_rpccred); -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
