[PATCH] block: no show partitions if partno corrupted

[Edward Adam Davis <eadavis@qq.com>]

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@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fcee6b76cf2e261c51a4
Tested-by: syzbot+fcee6b76cf2e261c51a4@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 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),
-- 
2.47.0