From 5ad533e8e65092be962e414e0417112c65d154fb Mon Sep 17 00:00:00 2001 From: Wilco Dijkstra Date: Fri, 10 May 2019 16:38:21 +0100 Subject: [PATCH] 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. --- ChangeLog | 7 +++++++ malloc/malloc.c | 9 +++++++-- manual/tunables.texi | 4 ++-- 3 files changed, 16 insertions(+), 4 deletions(-) diff --git a/ChangeLog b/ChangeLog index 185730361d..1ec840cf2b 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,10 @@ +2019-05-10 Wilco Dijkstra + + [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 * nptl/sem_close.c (struct walk_closure): Define. diff --git a/malloc/malloc.c b/malloc/malloc.c index 0e3d4dd516..b8baaa2706 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 749cabff1b..ae638823a2 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 -- 2.43.5