Re: [PATCH] block: no show partitions if partno corrupted

[Hannes Reinecke]

On 1/14/25 03:28, Edward Adam Davis wrote:
> syzbot reported a global-out-of-bounds in number. [1]
>
> Corrupted partno causes out-of-bounds access when accessing the hex_asc_upper
> array.
>
> To avoid this issue, skip partitions with partno greater than DISK_MAX_PARTS.
>
> [1]
> BUG: KASAN: global-out-of-bounds in number+0x3be/0xf40 lib/vsprintf.c:494
> Read of size 1 at addr ffffffff8c5fc971 by task syz-executor351/5832
>
> CPU: 0 UID: 0 PID: 5832 Comm: syz-executor351 Not tainted 6.13.0-rc6-next-20250107-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:94 [inline]
>   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>   print_address_description mm/kasan/report.c:378 [inline]
>   print_report+0x169/0x550 mm/kasan/report.c:489
>   kasan_report+0x143/0x180 mm/kasan/report.c:602
>   number+0x3be/0xf40 lib/vsprintf.c:494
>   pointer+0x764/0x1210 lib/vsprintf.c:2484
>   vsnprintf+0x75a/0x1220 lib/vsprintf.c:2846
>   seq_vprintf fs/seq_file.c:391 [inline]
>   seq_printf+0x172/0x270 fs/seq_file.c:406
>   show_partition+0x29f/0x3f0 block/genhd.c:905
>   seq_read_iter+0x969/0xd70 fs/seq_file.c:272
>   proc_reg_read_iter+0x1c2/0x290 fs/proc/inode.c:299
>   copy_splice_read+0x63a/0xb40 fs/splice.c:365
>   do_splice_read fs/splice.c:985 [inline]
>   splice_direct_to_actor+0x4af/0xc80 fs/splice.c:1089
>   do_splice_direct_actor fs/splice.c:1207 [inline]
>   do_splice_direct+0x289/0x3e0 fs/splice.c:1233
>   do_sendfile+0x564/0x8a0 fs/read_write.c:1363
>   __do_sys_sendfile64 fs/read_write.c:1424 [inline]
>   __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1410
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Reported-by: syzbot+fcee6b76cf2e261c51a4@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=fcee6b76cf2e261c51a4
> Tested-by: syzbot+fcee6b76cf2e261c51a4@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
> ---
>   block/genhd.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/block/genhd.c b/block/genhd.c
> index 9130e163e191..8d539a4a3b37 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -890,7 +890,9 @@ static int show_partition(struct seq_file *seqf, void *v)
>   
>   	rcu_read_lock();
>   	xa_for_each(&sgp->part_tbl, idx, part) {
> -		if (!bdev_nr_sectors(part))
> +		int partno = bdev_partno(part);
> +
> +		if (!bdev_nr_sectors(part) || partno >= DISK_MAX_PARTS)
>   			continue;
>   		seq_printf(seqf, "%4d  %7d %10llu %pg\n",
>   			   MAJOR(part->bd_dev), MINOR(part->bd_dev),
Maybe a warning is in order; when we are hitting this issue it means
that linux has a limitation on causing it to ignore the (otherwise 
valid) partition entry.

Otherwise looks good.

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich