From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Skripkin Subject: Re: [PATCH] net: 6pack: fix slab-out-of-bounds in decode_data Date: Fri, 13 Aug 2021 18:09:16 +0300 Message-ID: <0c5bc329-6555-edb1-82ad-038cae6b0299@gmail.com> References: <20210813112855.11170-1-paskripkin@gmail.com> <20210813145834.GC1931@kadam> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=W2ooleetOGxDv6uA8BJbyCwodwSrc5h12weH35wLF8I=; b=LJ9tvuR18O6i0e/19G+GiF5PLODO5+OHXzP8X61oleHa7rd6+QZyTd6vEpzqW2nXn+ JDqJfOqlhI8p6liS+aKZsi6CckOgV/mBo8Dzrlo8LzuzZN3w0uAsjztKJ6aFy+ufc7cK 129Rolwxw+GSezhVuAAHNlKRpk4nHjreaayZaNc49Yaj1IqmdANowcLxZeu9ZHDVnX06 bWXMHSJiLIQYEI7I/LZLRvxON0xhRKY1f/dl6ly4db+NMPe+CaN7ku0/Nl33rX8W94DA JZeJjhLohf4vBFmm0lGY92hwz1jsKutn6FLLA0VYrG7fEHYCWsYGsOIwyzaoieZ8SBo+ FAbw== In-Reply-To: <20210813145834.GC1931@kadam> Content-Language: en-US List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Dan Carpenter Cc: ajk@comnets.uni-bremen.de, davem@davemloft.net, kuba@kernel.org, linux-hams@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+fc8cd9a673d4577fb2e4@syzkaller.appspotmail.com On 8/13/21 5:58 PM, Dan Carpenter wrote: > On Fri, Aug 13, 2021 at 02:28:55PM +0300, Pavel Skripkin wrote: >> 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 >> --- >> 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..f4ffc2a80ab7 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 + 3 >= sizeof(sp->cooked_buf)) { > > It should be + 2 instead of + 3. > > We write three bytes. idx, idx + 1, idx + 2. Otherwise, good fix! > Indeed. Will fix in v2, thank you for pointing it out! With regards, Pavel Skripkin