From d74e6f6c0de55fc588b1ac09c88eb0fb8b8600af Mon Sep 17 00:00:00 2001 From: Wilco Dijkstra Date: Thu, 19 Oct 2017 18:19:55 +0100 Subject: Fix deadlock in _int_free consistency check This patch fixes a deadlock in the fastbin consistency check. If we fail the fast check due to concurrent modifications to the next chunk or system_mem, we should not lock if we already have the arena lock. Simplify the check to make it obviously correct. * malloc/malloc.c (_int_free): Fix deadlock bug in consistency check. --- malloc/malloc.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) (limited to 'malloc') diff --git a/malloc/malloc.c b/malloc/malloc.c index 6b789685ad..3d7c23917c 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -4135,17 +4135,20 @@ _int_free (mstate av, mchunkptr p, int have_lock) || __builtin_expect (chunksize (chunk_at_offset (p, size)) >= av->system_mem, 0)) { + bool fail = true; /* We might not have a lock at this point and concurrent modifications - of system_mem might have let to a false positive. Redo the test - after getting the lock. */ - if (!have_lock - || ({ __libc_lock_lock (av->mutex); - chunksize_nomask (chunk_at_offset (p, size)) <= 2 * SIZE_SZ - || chunksize (chunk_at_offset (p, size)) >= av->system_mem; - })) + of system_mem might result in a false positive. Redo the test after + getting the lock. */ + if (!have_lock) + { + __libc_lock_lock (av->mutex); + fail = (chunksize_nomask (chunk_at_offset (p, size)) <= 2 * SIZE_SZ + || chunksize (chunk_at_offset (p, size)) >= av->system_mem); + __libc_lock_unlock (av->mutex); + } + + if (fail) malloc_printerr ("free(): invalid next size (fast)"); - if (! have_lock) - __libc_lock_unlock (av->mutex); } free_perturb (chunk2mem(p), size - 2 * SIZE_SZ); -- cgit v1.2.1