Re: [PATCH v2 resend 1/2] scsi:scsi_debug: Fix out-of-bound read in resp_readcap16

[Douglas Gilbert <dgilbert@interlog.com>]

On 2021-10-12 11:39 p.m., Ye Bin wrote:
> We got following warning when runing syzkaller:
> [ 3813.830724] sg_write: data in/out 65466/242 bytes for SCSI command 0x9e-- guessing data in;
> [ 3813.830724]    program syz-executor not setting count and/or reply_len properly
> [ 3813.836956] ==================================================================
> [ 3813.839465] BUG: KASAN: stack-out-of-bounds in sg_copy_buffer+0x157/0x1e0
> [ 3813.841773] Read of size 4096 at addr ffff8883cf80f540 by task syz-executor/1549
> [ 3813.846612] Call Trace:
> [ 3813.846995]  dump_stack+0x108/0x15f
> [ 3813.847524]  print_address_description+0xa5/0x372
> [ 3813.848243]  kasan_report.cold+0x236/0x2a8
> [ 3813.849439]  check_memory_region+0x240/0x270
> [ 3813.850094]  memcpy+0x30/0x80
> [ 3813.850553]  sg_copy_buffer+0x157/0x1e0
> [ 3813.853032]  sg_copy_from_buffer+0x13/0x20
> [ 3813.853660]  fill_from_dev_buffer+0x135/0x370
> [ 3813.854329]  resp_readcap16+0x1ac/0x280
> [ 3813.856917]  schedule_resp+0x41f/0x1630
> [ 3813.858203]  scsi_debug_queuecommand+0xb32/0x17e0
> [ 3813.862699]  scsi_dispatch_cmd+0x330/0x950
> [ 3813.863329]  scsi_request_fn+0xd8e/0x1710
> [ 3813.863946]  __blk_run_queue+0x10b/0x230
> [ 3813.864544]  blk_execute_rq_nowait+0x1d8/0x400
> [ 3813.865220]  sg_common_write.isra.0+0xe61/0x2420
> [ 3813.871637]  sg_write+0x6c8/0xef0
> [ 3813.878853]  __vfs_write+0xe4/0x800
> [ 3813.883487]  vfs_write+0x17b/0x530
> [ 3813.884008]  ksys_write+0x103/0x270
> [ 3813.886268]  __x64_sys_write+0x77/0xc0
> [ 3813.886841]  do_syscall_64+0x106/0x360
> [ 3813.887415]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> We can reproduce this issue with following syzkaller log:
> r0 = openat(0xffffffffffffff9c, &(0x7f0000000040)='./file0\x00', 0x26e1, 0x0)
> r1 = syz_open_procfs(0xffffffffffffffff, &(0x7f0000000000)='fd/3\x00')
> open_by_handle_at(r1, &(0x7f00000003c0)=ANY=[@ANYRESHEX], 0x602000)
> r2 = syz_open_dev$sg(&(0x7f0000000000), 0x0, 0x40782)
> write$binfmt_aout(r2, &(0x7f0000000340)=ANY=[@ANYBLOB="00000000deff000000000000000000000000000000000000000000000000000047f007af9e107a41ec395f1bded7be24277a1501ff6196a83366f4e6362bc0ff2b247f68a972989b094b2da4fb3607fcf611a22dd04310d28c75039d"], 0x126)
> 
> As in resp_readcap16 we get "int alloc_len" value -1104926854, and then pass
> huge arr_len to fill_from_dev_buffer, but arr is only has 32 bytes space. So
> lead to OOB in sg_copy_buffer.
> To solve this issue just define alloc_len with U32 type.
> 
> Signed-off-by: Ye Bin <yebin10@huawei.com>

Acked-by: Douglas Gilbert <dgilbert@interlog.com>

Thanks.

> ---
>   drivers/scsi/scsi_debug.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index 66f507469a31..be0440545744 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -1856,7 +1856,7 @@ static int resp_readcap16(struct scsi_cmnd *scp,
>   {
>   	unsigned char *cmd = scp->cmnd;
>   	unsigned char arr[SDEBUG_READCAP16_ARR_SZ];
> -	int alloc_len;
> +	u32 alloc_len;
>   
>   	alloc_len = get_unaligned_be32(cmd + 10);
>   	/* following just in case virtual_gb changed */
> @@ -1885,7 +1885,7 @@ static int resp_readcap16(struct scsi_cmnd *scp,
>   	}
>   
>   	return fill_from_dev_buffer(scp, arr,
> -			    min_t(int, alloc_len, SDEBUG_READCAP16_ARR_SZ));
> +			    min_t(u32, alloc_len, SDEBUG_READCAP16_ARR_SZ));
>   }
>   
>   #define SDEBUG_MAX_TGTPGS_ARR_SZ 1412
>