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commit affec03b713c82c43a5b025dddc21bde3334f41e
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Mon Nov 26 20:06:37 2018 +0100
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malloc: tcache: Validate tc_idx before checking for double-frees [BZ #23907]
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The previous check could read beyond the end of the tcache entry
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array. If the e->key == tcache cookie check happened to pass, this
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would result in crashes.
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diff --git a/malloc/malloc.c b/malloc/malloc.c
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index c6b0282e783eaeea..13c52f376859562d 100644
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--- a/malloc/malloc.c
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+++ b/malloc/malloc.c
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@@ -4159,33 +4159,33 @@ _int_free (mstate av, mchunkptr p, int have_lock)
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#if USE_TCACHE
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{
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size_t tc_idx = csize2tidx (size);
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-
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- /* Check to see if it's already in the tcache. */
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- tcache_entry *e = (tcache_entry *) chunk2mem (p);
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-
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- /* This test succeeds on double free. However, we don't 100%
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- trust it (it also matches random payload data at a 1 in
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- 2^<size_t> chance), so verify it's not an unlikely coincidence
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- before aborting. */
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- if (__glibc_unlikely (e->key == tcache && tcache))
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+ if (tcache != NULL && tc_idx < mp_.tcache_bins)
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{
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- tcache_entry *tmp;
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- LIBC_PROBE (memory_tcache_double_free, 2, e, tc_idx);
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- for (tmp = tcache->entries[tc_idx];
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- tmp;
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- tmp = tmp->next)
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- if (tmp == e)
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- malloc_printerr ("free(): double free detected in tcache 2");
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- /* If we get here, it was a coincidence. We've wasted a few
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- cycles, but don't abort. */
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- }
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+ /* Check to see if it's already in the tcache. */
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+ tcache_entry *e = (tcache_entry *) chunk2mem (p);
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+
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+ /* This test succeeds on double free. However, we don't 100%
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+ trust it (it also matches random payload data at a 1 in
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+ 2^<size_t> chance), so verify it's not an unlikely
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+ coincidence before aborting. */
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+ if (__glibc_unlikely (e->key == tcache))
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+ {
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+ tcache_entry *tmp;
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+ LIBC_PROBE (memory_tcache_double_free, 2, e, tc_idx);
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+ for (tmp = tcache->entries[tc_idx];
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+ tmp;
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+ tmp = tmp->next)
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+ if (tmp == e)
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+ malloc_printerr ("free(): double free detected in tcache 2");
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+ /* If we get here, it was a coincidence. We've wasted a
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+ few cycles, but don't abort. */
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+ }
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- if (tcache
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- && tc_idx < mp_.tcache_bins
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- && tcache->counts[tc_idx] < mp_.tcache_count)
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- {
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- tcache_put (p, tc_idx);
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- return;
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+ if (tcache->counts[tc_idx] < mp_.tcache_count)
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+ {
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+ tcache_put (p, tc_idx);
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+ return;
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+ }
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}
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}
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#endif
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