From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58817) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZHxqB-0003Lz-8u for qemu-devel@nongnu.org; Wed, 22 Jul 2015 13:30:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZHxq9-0006fo-Nj for qemu-devel@nongnu.org; Wed, 22 Jul 2015 13:29:59 -0400 References: <38895e508e45514fbafafe437e25375b66731942.1437495012.git.jcody@redhat.com> <55AFCC8A.3020502@redhat.com> <20150722172608.GA6814@localhost.localdomain> From: Max Reitz Message-ID: <55AFD30B.7040105@redhat.com> Date: Wed, 22 Jul 2015 19:29:47 +0200 MIME-Version: 1.0 In-Reply-To: <20150722172608.GA6814@localhost.localdomain> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v2 1/2] block: vpc - prevent overflow if max_table_entries >= 0x40000000 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jeff Cody Cc: kwolf@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org On 22.07.2015 19:26, Jeff Cody wrote: > On Wed, Jul 22, 2015 at 07:02:02PM +0200, Max Reitz wrote: >> On 21.07.2015 18:13, Jeff Cody wrote: >>> When we allocate the pagetable based on max_table_entries, we multiply >>> the max table entry value by 4 to accomodate a table of 32-bit integers. >>> However, max_table_entries is a uint32_t, and the VPC driver accepts >>> ranges for that entry over 0x40000000. So during this allocation: >>> >>> s->pagetable = qemu_try_blockalign(bs->file, s->max_table_entries * 4); >>> >>> The size arg overflows, allocating significantly less memory than >>> expected. >>> >>> Since qemu_try_blockalign() size argument is size_t, cast the >>> multiplication correctly to prevent overflow. >>> >>> The value of "max_table_entries * 4" is used elsewhere in the code as >>> well, so store the correct value for use in all those cases. >>> >>> We also check the Max Tables Entries value, to make sure that it is < >>> SIZE_MAX / 4, so we know the pagetable size will fit in size_t. >>> >>> Reported-by: Richard W.M. Jones >>> Signed-off-by: Jeff Cody >>> --- >>> block/vpc.c | 17 +++++++++++++---- >>> 1 file changed, 13 insertions(+), 4 deletions(-) >>> >>> diff --git a/block/vpc.c b/block/vpc.c >>> index 37572ba..6ef21e6 100644 >>> --- a/block/vpc.c >>> +++ b/block/vpc.c >>> @@ -168,6 +168,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags, >>> uint8_t buf[HEADER_SIZE]; >>> uint32_t checksum; >>> uint64_t computed_size; >>> + uint64_t pagetable_size; >>> int disk_type = VHD_DYNAMIC; >>> int ret; >>> >>> @@ -269,7 +270,16 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags, >>> goto fail; >>> } >>> >>> - s->pagetable = qemu_try_blockalign(bs->file, s->max_table_entries * 4); >>> + if (s->max_table_entries > SIZE_MAX / 4) { >>> + error_setg(errp, "Max Table Entries too large (%" PRId32 ")", >>> + s->max_table_entries); >>> + ret = -EINVAL; >>> + goto fail; >>> + } >>> + >>> + pagetable_size = (uint64_t) s->max_table_entries * 4; >>> + >>> + s->pagetable = qemu_try_blockalign(bs->file, pagetable_size); >>> if (s->pagetable == NULL) { >>> ret = -ENOMEM; >>> goto fail; >>> @@ -277,14 +287,13 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags, >>> >>> s->bat_offset = be64_to_cpu(dyndisk_header->table_offset); >>> >>> - ret = bdrv_pread(bs->file, s->bat_offset, s->pagetable, >>> - s->max_table_entries * 4); >>> + ret = bdrv_pread(bs->file, s->bat_offset, s->pagetable, pagetable_size); >> >> The last parameter of bdrv_pread() is an int, so this will still >> overflow if s->max_table_entries > INT_MAX / 4. >> > > I thought about checking for INT_MAX overflow as well - I probably > should. I wasn't too concerned about it, however, as bdrv_read() will > return -EINVAL for nb_sectors < 0. Right, but SIZE_MAX may be larger than 2ull * INT_MAX, so on 64 bit systems, pagetable_size might become large enough for (int)pagetable_size to be positive, with (int)pagetable_size != pagetable_size, which would make bdrv_pread() work just fine, but only read a part of the table. Max >>> if (ret < 0) { >>> goto fail; >>> } >>> >>> s->free_data_block_offset = >>> - (s->bat_offset + (s->max_table_entries * 4) + 511) & ~511; >>> + (s->bat_offset + pagetable_size + 511) & ~511; >> >> Not necessary, but perhaps we should be using ROUND_UP() here... >> > > Sure, why not :) > >> Max >> >>> for (i = 0; i < s->max_table_entries; i++) { >>> be32_to_cpus(&s->pagetable[i]); >>> >>