diff options
authorMax Reitz <mreitz@redhat.com>2017-11-14 19:41:27 +0100
committerMax Reitz <mreitz@redhat.com>2017-11-17 18:21:31 +0100
commit08546bcfb260c28141e27cf3367c443528602fc0 (patch)
parent4efb1f7c612ff35badc8f8cbda78ac891fabf20a (diff)
qcow2: Fix overly broad madvise()
@mem_size and @offset are both size_t, thus subtracting them from one another will just return a big size_t if mem_size < offset -- even more obvious here because the result is stored in another size_t. Checking that result to be positive is therefore not sufficient to exclude the case that offset > mem_size. Thus, we currently sometimes issue an madvise() over a very large address range. This is triggered by iotest 163, but with -m64, this does not result in tangible problems. But with -m32, this test produces three segfaults, all of which are fixed by this patch. Signed-off-by: Max Reitz <mreitz@redhat.com> Message-id: 20171114184127.24238-1-mreitz@redhat.com Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Alberto Garcia <berto@igalia.com> Reviewed-by: Darren Kenny <darren.kenny@oracle.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
1 files changed, 1 insertions, 1 deletions
diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index a5baaba0ff..c48ffebd8f 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -85,7 +85,7 @@ static void qcow2_cache_table_release(BlockDriverState *bs, Qcow2Cache *c,
size_t mem_size = (size_t) s->cluster_size * num_tables;
size_t offset = QEMU_ALIGN_UP((uintptr_t) t, align) - (uintptr_t) t;
size_t length = QEMU_ALIGN_DOWN(mem_size - offset, align);
- if (length > 0) {
+ if (mem_size > offset && length > 0) {
madvise((uint8_t *) t + offset, length, MADV_DONTNEED);