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authorEric Biggers <ebiggers@google.com>2017-11-15 16:38:09 -0800
committerMike Snitzer <snitzer@redhat.com>2017-11-16 16:49:57 -0500
commit74d4108d9e681dbbe4a2940ed8fdff1f6868184c (patch)
treea6fff902641076e347609e31cfe9fa293ef32cf9 /drivers/md
parent5d47c89f29eab6e9e224d7ac8c0baf4da72c9493 (diff)
dm bufio: fix integer overflow when limiting maximum cache size
The default max_cache_size_bytes for dm-bufio is meant to be the lesser of 25% of the size of the vmalloc area and 2% of the size of lowmem. However, on 32-bit systems the intermediate result in the expression (VMALLOC_END - VMALLOC_START) * DM_BUFIO_VMALLOC_PERCENT / 100 overflows, causing the wrong result to be computed. For example, on a 32-bit system where the vmalloc area is 520093696 bytes, the result is 1174405 rather than the expected 130023424, which makes the maximum cache size much too small (far less than 2% of lowmem). This causes severe performance problems for dm-verity users on affected systems. Fix this by using mult_frac() to correctly multiply by a percentage. Do this for all places in dm-bufio that multiply by a percentage. Also replace (VMALLOC_END - VMALLOC_START) with VMALLOC_TOTAL, which contrary to the comment is now defined in include/linux/vmalloc.h. Depends-on: 9993bc635 ("sched/x86: Fix overflow in cyc2ns_offset") Fixes: 95d402f057f2 ("dm: add bufio") Cc: <stable@vger.kernel.org> # v3.2+ Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md')
-rw-r--r--drivers/md/dm-bufio.c15
1 files changed, 6 insertions, 9 deletions
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index d216a8f7bc22..8e3adcb46851 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -974,7 +974,8 @@ static void __get_memory_limit(struct dm_bufio_client *c,
buffers = c->minimum_buffers;
*limit_buffers = buffers;
- *threshold_buffers = buffers * DM_BUFIO_WRITEBACK_PERCENT / 100;
+ *threshold_buffers = mult_frac(buffers,
+ DM_BUFIO_WRITEBACK_PERCENT, 100);
}
/*
@@ -1910,19 +1911,15 @@ static int __init dm_bufio_init(void)
memset(&dm_bufio_caches, 0, sizeof dm_bufio_caches);
memset(&dm_bufio_cache_names, 0, sizeof dm_bufio_cache_names);
- mem = (__u64)((totalram_pages - totalhigh_pages) *
- DM_BUFIO_MEMORY_PERCENT / 100) << PAGE_SHIFT;
+ mem = (__u64)mult_frac(totalram_pages - totalhigh_pages,
+ DM_BUFIO_MEMORY_PERCENT, 100) << PAGE_SHIFT;
if (mem > ULONG_MAX)
mem = ULONG_MAX;
#ifdef CONFIG_MMU
- /*
- * Get the size of vmalloc space the same way as VMALLOC_TOTAL
- * in fs/proc/internal.h
- */
- if (mem > (VMALLOC_END - VMALLOC_START) * DM_BUFIO_VMALLOC_PERCENT / 100)
- mem = (VMALLOC_END - VMALLOC_START) * DM_BUFIO_VMALLOC_PERCENT / 100;
+ if (mem > mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100))
+ mem = mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100);
#endif
dm_bufio_default_cache_size = mem;