Re: [syzbot] UBSAN: shift-out-of-bounds in xfrm_get_default

[Pavel Skripkin]

On 8/30/21 23:19, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    eaf2aaec0be4 Merge tag 'wireless-drivers-next-2021-08-29' ..
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1219326d300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d2f9d4c9ff8c5ae7
> dashboard link: https://syzkaller.appspot.com/bug?extid=b2be9dd8ca6f6c73ee2d
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11e6e3a9300000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10de8a6d300000
>
> The issue was bisected to:
>
> commit 2d151d39073aff498358543801fca0f670fea981
> Author: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
> Date:   Sun Jul 18 07:11:06 2021 +0000
>
>      xfrm: Add possibility to set the default to block if we have no policy
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=114523fe300000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=134523fe300000
> console output: https://syzkaller.appspot.com/x/log.txt?x=154523fe300000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b2be9dd8ca6f6c73ee2d@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 2d151d39073a ("xfrm: Add possibility to set the default to block if we have no policy")
>
> netlink: 172 bytes leftover after parsing attributes in process `syz-executor354'.
> ================================================================================
> UBSAN: shift-out-of-bounds in net/xfrm/xfrm_user.c:2010:49
> shift exponent 224 is too large for 32-bit type 'int'


#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git




With regards,
Pavel SkripkinFrom 0395839028b13f4e380e167c6381e4eea4a9fc42 Mon Sep 17 00:00:00 2001
From: Pavel Skripkin <paskripkin@xxxxxxxxx>
Date: Wed, 1 Sep 2021 21:55:25 +0300
Subject: [PATCH] net: xfrm: fix shift-out-of-bounds in xfrm_get_default

/* ... */

Signed-off-by: Pavel Skripkin <paskripkin@xxxxxxxxx>
---
 net/xfrm/xfrm_user.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index b7b986520dc7..a1dd38525957 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2007,6 +2007,9 @@ static int xfrm_get_default(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	r_up = nlmsg_data(r_nlh);
 
+	if (up->dirmask >= XFRM_USERPOLICY_DIRMASK_MAX)
+		return -EINVAL;
+
 	r_up->action = ((net->xfrm.policy_default & (1 << up->dirmask)) >> up->dirmask);
 	r_up->dirmask = up->dirmask;
 	nlmsg_end(r_skb, r_nlh);
-- 
2.33.0