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From: Pavel Skripkin <paskripkin@gmail.com>
To: ajk@comnets.uni-bremen.de, davem@davemloft.net, kuba@kernel.org
Cc: linux-hams@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, dan.carpenter@oracle.com,
	Pavel Skripkin <paskripkin@gmail.com>,
	syzbot+fc8cd9a673d4577fb2e4@syzkaller.appspotmail.com
Subject: [PATCH v2] net: 6pack: fix slab-out-of-bounds in decode_data
Date: Fri, 13 Aug 2021 18:14:33 +0300	[thread overview]
Message-ID: <20210813151433.22493-1-paskripkin@gmail.com> (raw)
In-Reply-To: <20210813145834.GC1931@kadam>

Syzbot reported slab-out-of bounds write in decode_data().
The problem was in missing validation checks.

Syzbot's reproducer generated malicious input, which caused
decode_data() to be called a lot in sixpack_decode(). Since
rx_count_cooked is only 400 bytes and noone reported before,
that 400 bytes is not enough, let's just check if input is malicious
and complain about buffer overrun.

Fail log:
==================================================================
BUG: KASAN: slab-out-of-bounds in drivers/net/hamradio/6pack.c:843
Write of size 1 at addr ffff888087c5544e by task kworker/u4:0/7

CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 5.6.0-rc3-syzkaller #0
...
Workqueue: events_unbound flush_to_ldisc
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x197/0x210 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
 __kasan_report.cold+0x1b/0x32 mm/kasan/report.c:506
 kasan_report+0x12/0x20 mm/kasan/common.c:641
 __asan_report_store1_noabort+0x17/0x20 mm/kasan/generic_report.c:137
 decode_data.part.0+0x23b/0x270 drivers/net/hamradio/6pack.c:843
 decode_data drivers/net/hamradio/6pack.c:965 [inline]
 sixpack_decode drivers/net/hamradio/6pack.c:968 [inline]

Reported-and-tested-by: syzbot+fc8cd9a673d4577fb2e4@syzkaller.appspotmail.com
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---

Changes in v2:
	+ 3 -> +2 (Reported by Dan Carpenter)

---
 drivers/net/hamradio/6pack.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
index fcf3af76b6d7..8fe8887d506a 100644
--- a/drivers/net/hamradio/6pack.c
+++ b/drivers/net/hamradio/6pack.c
@@ -827,6 +827,12 @@ static void decode_data(struct sixpack *sp, unsigned char inbyte)
 		return;
 	}
 
+	if (sp->rx_count_cooked + 2 >= sizeof(sp->cooked_buf)) {
+		pr_err("6pack: cooked buffer overrun, data loss\n");
+		sp->rx_count = 0;
+		return;
+	}
+
 	buf = sp->raw_buf;
 	sp->cooked_buf[sp->rx_count_cooked++] =
 		buf[0] | ((buf[1] << 2) & 0xc0);
-- 
2.32.0


  parent reply	other threads:[~2021-08-13 15:22 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-13 11:28 [PATCH] " Pavel Skripkin
2021-08-13 14:58 ` Dan Carpenter
2021-08-13 15:09   ` Pavel Skripkin
2021-08-13 15:14   ` Pavel Skripkin [this message]
2021-08-13 21:09     ` [PATCH v2] " Dan Carpenter
2021-08-13 21:32       ` Pavel Skripkin
2021-08-16 10:10     ` patchwork-bot+netdevbpf
2021-08-14  0:23   ` [PATCH] " Kevin Dawson
2021-08-14 14:17     ` Pavel Skripkin
2021-08-16  7:13       ` Dan Carpenter

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