diff options
Diffstat (limited to 'malloc')
| -rw-r--r-- | malloc/malloc.c | 20 |
1 files changed, 12 insertions, 8 deletions
diff --git a/malloc/malloc.c b/malloc/malloc.c index b1668b501b..5e419adac4 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -3783,25 +3783,29 @@ _int_free(mstate av, mchunkptr p, int have_lock) unsigned int idx = fastbin_index(size); fb = &fastbin (av, idx); - mchunkptr fd; - mchunkptr old = *fb; + /* Atomically link P to its fastbin: P->FD = *FB; *FB = P; */ + mchunkptr old = *fb, old2; unsigned int old_idx = ~0u; do { - /* Another simple check: make sure the top of the bin is not the - record we are going to add (i.e., double free). */ + /* Check that the top of the bin is not the record we are going to add + (i.e., double free). */ if (__builtin_expect (old == p, 0)) { errstr = "double free or corruption (fasttop)"; goto errout; } - if (old != NULL) + /* Check that size of fastbin chunk at the top is the same as + size of the chunk that we are adding. We can dereference OLD + only if we have the lock, otherwise it might have already been + deallocated. See use of OLD_IDX below for the actual check. */ + if (have_lock && old != NULL) old_idx = fastbin_index(chunksize(old)); - p->fd = fd = old; + p->fd = old2 = old; } - while ((old = catomic_compare_and_exchange_val_rel (fb, p, fd)) != fd); + while ((old = catomic_compare_and_exchange_val_rel (fb, p, old2)) != old2); - if (fd != NULL && __builtin_expect (old_idx != idx, 0)) + if (have_lock && old != NULL && __builtin_expect (old_idx != idx, 0)) { errstr = "invalid fastbin entry (free)"; goto errout; |