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malloc: tcache: detect infinite-loop in _int_free when freeing tcache [BZ#27052]

Message ID 20201211140643.2476907-1-ssmallkirby@gmail.com
State Committed
Headers show
Series malloc: tcache: detect infinite-loop in _int_free when freeing tcache [BZ#27052] | expand

Commit Message

W. Hashimoto Dec. 11, 2020, 2:06 p.m. UTC
If linked-list of tcache contains a loop, it invokes infinite
loop in _int_free when freeing tcache. The PoC which invokes
such infinite loop is on the Bugzilla(#27052). This loop
should terminate when the loop exceeds mp_.tcache_count and
the program should abort. The affected glibc version is
2.29 or later.
 malloc/malloc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
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diff --git a/malloc/malloc.c b/malloc/malloc.c
index 5b87bdb081..aadae327bf 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -4224,11 +4224,14 @@  _int_free (mstate av, mchunkptr p, int have_lock)
 	if (__glibc_unlikely (e->key == tcache))
 	    tcache_entry *tmp;
+           size_t cnt = 0;
 	    LIBC_PROBE (memory_tcache_double_free, 2, e, tc_idx);
 	    for (tmp = tcache->entries[tc_idx];
-		 tmp = REVEAL_PTR (tmp->next))
+		 tmp = REVEAL_PTR (tmp->next), ++cnt)
+               if (cnt >= mp_.tcache_count)
+                 malloc_printerr ("free(): too many chunks detected in tcache");
 		if (__glibc_unlikely (!aligned_OK (tmp)))
 		  malloc_printerr ("free(): unaligned chunk detected in tcache 2");
 		if (tmp == e)