From: Pavel Skripkin paskripkin@gmail.com

stable inclusion from linux-4.19.205 commit 4e370cc081a78ee23528311ca58fd98a06768ec7 CVE: CVE-2021-42008

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[ Upstream commit 19d1532a187669ce86d5a2696eb7275310070793 ]

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 Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Yang Yingliang yangyingliang@huawei.com Reviewed-by: Xiu Jianfeng xiujianfeng@huawei.com --- 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 8c636c4932274..1001e9a2edd4f 100644 --- a/drivers/net/hamradio/6pack.c +++ b/drivers/net/hamradio/6pack.c @@ -859,6 +859,12 @@ 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);