From 19d1532a187669ce86d5a2696eb7275310070793 Mon Sep 17 00:00:00 2001 From: Pavel Skripkin Date: Fri, 13 Aug 2021 18:14:33 +0300 Subject: [PATCH] net: 6pack: fix slab-out-of-bounds in decode_data 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 Reviewed-by: Dan Carpenter Signed-off-by: David S. Miller --- 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 fcf3af76b6d7b..8fe8887d506a3 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); -- 2.39.5