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authorWilco Dijkstra <wdijkstr@arm.com>2019-05-10 16:38:21 +0100
committerWilco Dijkstra <wdijkstr@arm.com>2019-05-10 16:38:21 +0100
commit5ad533e8e65092be962e414e0417112c65d154fb (patch)
treebb926e04c328e70f54fc026cbee805c52d9b2f6d
parent4aee85f96b881c1cb80a1fff752b8e2130a9a4d9 (diff)
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Fix tcache count maximum (BZ #24531)
The tcache counts[] array is a char, which has a very small range and thus may overflow. When setting tcache_count tunable, there is no overflow check. However the tunable must not be larger than the maximum value of the tcache counts[] array, otherwise it can overflow when filling the tcache. [BZ #24531] * malloc/malloc.c (MAX_TCACHE_COUNT): New define. (do_set_tcache_count): Only update if count is small enough. * manual/tunables.texi (glibc.malloc.tcache_count): Document max value.
-rw-r--r--ChangeLog7
-rw-r--r--malloc/malloc.c9
-rw-r--r--manual/tunables.texi4
3 files changed, 16 insertions, 4 deletions
diff --git a/ChangeLog b/ChangeLog
index 185730361d7..1ec840cf2bc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2019-05-10 Wilco Dijkstra <wdijkstr@arm.com>
+
+ [BZ #24531]
+ * malloc/malloc.c (MAX_TCACHE_COUNT): New define.
+ (do_set_tcache_count): Only update if count is small enough.
+ * manual/tunables.texi (glibc.malloc.tcache_count): Document max value.
+
2019-05-10 Florian Weimer <fweimer@redhat.com>
* nptl/sem_close.c (struct walk_closure): Define.
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 0e3d4dd5163..b8baaa2706d 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -2905,6 +2905,8 @@ typedef struct tcache_perthread_struct
tcache_entry *entries[TCACHE_MAX_BINS];
} tcache_perthread_struct;
+#define MAX_TCACHE_COUNT 127 /* Maximum value of counts[] entries. */
+
static __thread bool tcache_shutting_down = false;
static __thread tcache_perthread_struct *tcache = NULL;
@@ -5098,8 +5100,11 @@ do_set_tcache_max (size_t value)
static __always_inline int
do_set_tcache_count (size_t value)
{
- LIBC_PROBE (memory_tunable_tcache_count, 2, value, mp_.tcache_count);
- mp_.tcache_count = value;
+ if (value <= MAX_TCACHE_COUNT)
+ {
+ LIBC_PROBE (memory_tunable_tcache_count, 2, value, mp_.tcache_count);
+ mp_.tcache_count = value;
+ }
return 1;
}
diff --git a/manual/tunables.texi b/manual/tunables.texi
index 749cabff1b0..ae638823a21 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -189,8 +189,8 @@ per-thread cache. The default (and maximum) value is 1032 bytes on
@deftp Tunable glibc.malloc.tcache_count
The maximum number of chunks of each size to cache. The default is 7.
-There is no upper limit, other than available system memory. If set
-to zero, the per-thread cache is effectively disabled.
+The upper limit is 127. If set to zero, the per-thread cache is effectively
+disabled.
The approximate maximum overhead of the per-thread cache is thus equal
to the number of bins times the chunk count in each bin times the size