[NETFILTER]: nf_conntrack: fix use-after-free in helper destroy callback invocation When the helper module is removed for a master connection that has a fulfilled expectation, but has already timed out and got removed from the hash tables, nf_conntrack_helper_unregister can't find the master connection to unset the helper, causing a use-after-free when the expected connection is destroyed and releases the last reference to the master. The helper destroy callback was introduced for the PPtP helper to clean up expectations and expected connections when the master connection times out, but doing this from destroy_conntrack only works for unfulfilled expectations since expected connections hold a reference to the master, preventing its destruction. Move the destroy callback to the timeout function, which fixes both problems. Reported/tested by Gabor Burjan . Signed-off-by: Patrick McHardy --- commit a49738a0ca6dbe54bbc6672b52286ed6b1d8f4ce tree aa2324f3dd628d3b74f6c6d57355b11adb2212d3 parent af3b146d26550f0c8e0d77b2117c6f8aec5d8146 author Patrick McHardy Wed, 16 May 2007 18:51:42 +0200 committer Patrick McHardy Wed, 16 May 2007 18:51:42 +0200 net/netfilter/nf_conntrack_core.c | 8 ++++---- 1 files changed, 4 insertions(+), 4 deletions(-) diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index e8b5c2d..483e927 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -298,7 +298,6 @@ static void destroy_conntrack(struct nf_conntrack *nfct) { struct nf_conn *ct = (struct nf_conn *)nfct; - struct nf_conn_help *help = nfct_help(ct); struct nf_conntrack_l4proto *l4proto; typeof(nf_conntrack_destroyed) destroyed; @@ -309,9 +308,6 @@ destroy_conntrack(struct nf_conntrack *nfct) nf_conntrack_event(IPCT_DESTROY, ct); set_bit(IPS_DYING_BIT, &ct->status); - if (help && help->helper && help->helper->destroy) - help->helper->destroy(ct); - /* To make sure we don't get any weird locking issues here: * destroy_conntrack() MUST NOT be called with a write lock * to nf_conntrack_lock!!! -HW */ @@ -353,6 +349,10 @@ destroy_conntrack(struct nf_conntrack *nfct) static void death_by_timeout(unsigned long ul_conntrack) { struct nf_conn *ct = (void *)ul_conntrack; + struct nf_conn_help *help = nfct_help(ct); + + if (help && help->helper && help->helper->destroy) + help->helper->destroy(ct); write_lock_bh(&nf_conntrack_lock); /* Inside lock so preempt is disabled on module removal path.