Messages in this thread Patch in this message | | | Date | Wed, 21 Feb 2024 14:15:46 +0100 | From | Florian Westphal <> | Subject | Re: [syzbot] [net?] WARNING in mpls_gso_segment |
| |
syzbot <syzbot+99d15fcdb0132a1e1a82@syzkaller.appspotmail.com> wrote: > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1536462c180000 > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/adbf5d8e38d7/disk-49344462.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/0f8e3fb78410/vmlinux-49344462.xz > kernel image: https://storage.googleapis.com/syzbot-assets/682f4814bf23/bzImage-49344462.xz > > The issue was bisected to: > > commit 219eee9c0d16f1b754a8b85275854ab17df0850a > Author: Florian Westphal <fw@strlen.de> > Date: Fri Feb 16 11:36:57 2024 +0000 > > net: skbuff: add overflow debug check to pull/push helpers > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13262752180000 > final oops: https://syzkaller.appspot.com/x/report.txt?x=10a62752180000 > console output: https://syzkaller.appspot.com/x/log.txt?x=17262752180000 > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+99d15fcdb0132a1e1a82@syzkaller.appspotmail.com > Fixes: 219eee9c0d16 ("net: skbuff: add overflow debug check to pull/push helpers") > > ------------[ cut here ]------------ > WARNING: CPU: 0 PID: 5068 at include/linux/skbuff.h:2723 pskb_may_pull_reason include/linux/skbuff.h:2723 [inline] > WARNING: CPU: 0 PID: 5068 at include/linux/skbuff.h:2723 pskb_may_pull include/linux/skbuff.h:2739 [inline] > WARNING: CPU: 0 PID: 5068 at include/linux/skbuff.h:2723 mpls_gso_segment+0x773/0xaa0 net/mpls/mpls_gso.c:34
Two possible solutions:
1.)
diff --git a/net/mpls/mpls_gso.c b/net/mpls/mpls_gso.c index 533d082f0701..43801b78dd64 100644 --- a/net/mpls/mpls_gso.c +++ b/net/mpls/mpls_gso.c @@ -25,12 +25,13 @@ static struct sk_buff *mpls_gso_segment(struct sk_buff *skb, netdev_features_t mpls_features; u16 mac_len = skb->mac_len; __be16 mpls_protocol; - unsigned int mpls_hlen; + int mpls_hlen; skb_reset_network_header(skb); mpls_hlen = skb_inner_network_header(skb) - skb_network_header(skb); - if (unlikely(!mpls_hlen || mpls_hlen % MPLS_HLEN)) + if (unlikely(mpls_hlen <= 0 || mpls_hlen % MPLS_HLEN)) goto out; + if (unlikely(!pskb_may_pull(skb, mpls_hlen))) goto out;
(or a variation thereof). 2) revert the pskb_may_pull_reason change added in 219eee9c0d16f1b754a8 to make it tolerant to "negative" (huge) may-pull requests again.
With above repro, skb_inner_network_header() yields 0, skb_network_header() returns 108, so we "pskb_may_pull(skb, -108)))" which now triggers DEBUG_NET_WARN_ON_ONCE() check.
Before blamed commit, this would make pskb_may_pull hit:
if (unlikely(len > skb->len)) return SKB_DROP_REASON_PKT_TOO_SMALL; and mpls_gso_segment takes the 'goto out' label.
So question is really if we should fix this in mpls_gso (and possible others that try to pull negative numbers...) or if we should legalize this, either by adding explicit if (unlikely(len > INT_MAX)) test to pskb_may_pull_reason or by adding a comment that negative 'len' numbers are expected to be caught by the check vs. skb->len. Opinions?
| |