From 19d1532a187669ce86d5a2696eb7275310070793 Mon Sep 17 00:00:00 2001
From: Pavel Skripkin <paskripkin@gmail.com>
Date: Fri, 13 Aug 2021 18:14:33 +0300
Subject: [PATCH] net: 6pack: fix slab-out-of-bounds in decode_data
Git-commit: 19d1532a187669ce86d5a2696eb7275310070793
Patch-mainline: v5.14-rc7
References: CVE-2021-42008 bsc#1191315
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>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
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);
--
2.26.2