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authorMaxim Kuvyrkov <maxim@kugelworks.com>2013-12-24 09:44:50 +1300
committerMaxim Kuvyrkov <maxim@kugelworks.com>2014-01-05 14:56:39 +1300
commit8b43a2274a593ce91e673db1cfac6e808134bc84 (patch)
tree563557cb2f148aadd2b928f9e7b900f8267d5de3
parentca0dd6386ed2b5c5c6ca392547628a1228432ae0 (diff)
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Fix race in free() of fastbin chunk: BZ #15073
Perform sanity check only if we have_lock. Due to lockless nature of fastbins we need to be careful derefencing pointers to fastbin entries (chunksize(old) in this case) in multithreaded environments. The fix is to add have_lock to the if-condition checks. The rest of the patch only makes code more readable. * malloc/malloc.c (_int_free): Perform sanity check only if we have_lock. Conflicts: ChangeLog NEWS
-rw-r--r--ChangeLog7
-rw-r--r--NEWS2
-rw-r--r--malloc/malloc.c20
3 files changed, 20 insertions, 9 deletions
diff --git a/ChangeLog b/ChangeLog
index 1e5efa74c03..74d433076e2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2014-01-04 Maxim Kuvyrkov <maxim@kugelworks.com>
+ Ondřej Bílka <neleai@seznam.cz>
+
+ [BZ #15073]
+ * malloc/malloc.c (_int_free): Perform sanity check only if we
+ have_lock.
+
2013-11-11 David S. Miller <davem@davemloft.net>
[BZ #16150]
diff --git a/NEWS b/NEWS
index 6c7aaa7c213..29856cc046f 100644
--- a/NEWS
+++ b/NEWS
@@ -9,7 +9,7 @@ Version 2.18.1
* The following bugs are resolved with this release:
- 15128, 15909, 15996, 16150.
+ 15073, 15128, 15909, 15996, 16150.
Version 2.18
diff --git a/malloc/malloc.c b/malloc/malloc.c
index be472b2ba38..8a0eb854e26 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -3809,25 +3809,29 @@ _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;