From b93f995081cc32e56071fef179161d2907d0491e Mon Sep 17 00:00:00 2001 From: Max Reitz Date: Tue, 29 Apr 2014 19:03:14 +0200 Subject: [PATCH] qcow2: Check min_size in qcow2_grow_l1_table() First, new_l1_size is an int64_t, whereas min_size is a uint64_t. Therefore, during the loop which adjusts new_l1_size until it equals or exceeds min_size, new_l1_size might overflow and become negative. The comparison in the loop condition however will take it as an unsigned value (because min_size is unsigned) and therefore recognize it as exceeding min_size. Therefore, the loop is left with a negative new_l1_size, which is not correct. This could be fixed by making new_l1_size uint64_t. On the other hand, however, by doing this, the while loop may take forever. If min_size is e.g. UINT64_MAX, it will take new_l1_size probably multiple overflows to reach the exact same value (if it reaches it at all). Then, right after the loop, new_l1_size will be recognized as being too big anyway. Both problems require a ridiculously high min_size value, which is very unlikely to occur; but both problems are also simply avoided by checking whether min_size is sane before calculating new_l1_size (which should still be checked separately, though). Signed-off-by: Max Reitz Signed-off-by: Kevin Wolf --- block/qcow2-cluster.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index b746429..76d2bcf 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -42,6 +42,13 @@ int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size, if (min_size <= s->l1_size) return 0; + /* Do a sanity check on min_size before trying to calculate new_l1_size + * (this prevents overflows during the while loop for the calculation of + * new_l1_size) */ + if (min_size > INT_MAX / sizeof(uint64_t)) { + return -EFBIG; + } + if (exact_size) { new_l1_size = min_size; } else { -- 2.7.4