From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57919) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZHxmq-0007aU-OI for qemu-devel@nongnu.org; Wed, 22 Jul 2015 13:26:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZHxmm-0005Q3-7T for qemu-devel@nongnu.org; Wed, 22 Jul 2015 13:26:32 -0400 Date: Wed, 22 Jul 2015 13:26:08 -0400 From: Jeff Cody Message-ID: <20150722172608.GA6814@localhost.localdomain> References: <38895e508e45514fbafafe437e25375b66731942.1437495012.git.jcody@redhat.com> <55AFCC8A.3020502@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55AFCC8A.3020502@redhat.com> 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: Max Reitz Cc: kwolf@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org 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. > > 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]); > > >