| Message ID | 20240216113700.23013-1-fw@strlen.de (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 219eee9c0d16f1b754a8b85275854ab17df0850a |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net] net: skbuff: add overflow debug check to pull/push helpers | expand |
On Fri, Feb 16, 2024 at 12:36:57PM +0100, Florian Westphal wrote: > syzbot managed to trigger following splat: > BUG: KASAN: use-after-free in __skb_flow_dissect+0x4a3b/0x5e50 > Read of size 1 at addr ffff888208a4000e by task a.out/2313 > [..] > __skb_flow_dissect+0x4a3b/0x5e50 > __skb_get_hash+0xb4/0x400 > ip_tunnel_xmit+0x77e/0x26f0 > ipip_tunnel_xmit+0x298/0x410 > .. > > Analysis shows that the skb has a valid ->head, but bogus ->data > pointer. > > skb->data gets its bogus value via the neigh layer, which does: > > 1556 __skb_pull(skb, skb_network_offset(skb)); > > ... and the skb was already dodgy at this point: > > skb_network_offset(skb) returns a negative value due to an > earlier overflow of skb->network_header (u16). __skb_pull thus > "adjusts" skb->data by a huge offset, pointing outside skb->head > area. > > Allow debug builds to splat when we try to pull/push more than > INT_MAX bytes. > > After this, the syzkaller reproducer yields a more precise splat > before the flow dissector attempts to read off skb->data memory: > > WARNING: CPU: 5 PID: 2313 at include/linux/skbuff.h:2653 neigh_connected_output+0x28e/0x400 > ip_finish_output2+0xb25/0xed0 > iptunnel_xmit+0x4ff/0x870 > ipgre_xmit+0x78e/0xbb0 > > Signed-off-by: Florian Westphal <fw@strlen.de> Reviewed-by: Simon Horman <horms@kernel.org>
On Fri, 2024-02-16 at 12:36 +0100, Florian Westphal wrote: > syzbot managed to trigger following splat: > BUG: KASAN: use-after-free in __skb_flow_dissect+0x4a3b/0x5e50 > Read of size 1 at addr ffff888208a4000e by task a.out/2313 > [..] > __skb_flow_dissect+0x4a3b/0x5e50 > __skb_get_hash+0xb4/0x400 > ip_tunnel_xmit+0x77e/0x26f0 > ipip_tunnel_xmit+0x298/0x410 > .. > > Analysis shows that the skb has a valid ->head, but bogus ->data > pointer. > > skb->data gets its bogus value via the neigh layer, which does: > > 1556 __skb_pull(skb, skb_network_offset(skb)); > > ... and the skb was already dodgy at this point: > > skb_network_offset(skb) returns a negative value due to an > earlier overflow of skb->network_header (u16). __skb_pull thus > "adjusts" skb->data by a huge offset, pointing outside skb->head > area. > > Allow debug builds to splat when we try to pull/push more than > INT_MAX bytes. > > After this, the syzkaller reproducer yields a more precise splat > before the flow dissector attempts to read off skb->data memory: > > WARNING: CPU: 5 PID: 2313 at include/linux/skbuff.h:2653 neigh_connected_output+0x28e/0x400 > ip_finish_output2+0xb25/0xed0 > iptunnel_xmit+0x4ff/0x870 > ipgre_xmit+0x78e/0xbb0 > > Signed-off-by: Florian Westphal <fw@strlen.de> This is targeting 'net', but IMHO looks more like 'net-next' material. Any objections applying the patch there? Thanks! Paolo
Paolo Abeni <pabeni@redhat.com> wrote: > This is targeting 'net', but IMHO looks more like 'net-next' material. > Any objections applying the patch there? No.
Hello: This patch was applied to netdev/net-next.git (main) by Paolo Abeni <pabeni@redhat.com>: On Fri, 16 Feb 2024 12:36:57 +0100 you wrote: > syzbot managed to trigger following splat: > BUG: KASAN: use-after-free in __skb_flow_dissect+0x4a3b/0x5e50 > Read of size 1 at addr ffff888208a4000e by task a.out/2313 > [..] > __skb_flow_dissect+0x4a3b/0x5e50 > __skb_get_hash+0xb4/0x400 > ip_tunnel_xmit+0x77e/0x26f0 > ipip_tunnel_xmit+0x298/0x410 > .. > > [...] Here is the summary with links: - [net] net: skbuff: add overflow debug check to pull/push helpers https://git.kernel.org/netdev/net-next/c/219eee9c0d16 You are awesome, thank you!
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 2dde34c29203..fd9198fcc3c3 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2642,6 +2642,8 @@ static inline void skb_put_u8(struct sk_buff *skb, u8 val) void *skb_push(struct sk_buff *skb, unsigned int len); static inline void *__skb_push(struct sk_buff *skb, unsigned int len) { + DEBUG_NET_WARN_ON_ONCE(len > INT_MAX); + skb->data -= len; skb->len += len; return skb->data; @@ -2650,6 +2652,8 @@ static inline void *__skb_push(struct sk_buff *skb, unsigned int len) void *skb_pull(struct sk_buff *skb, unsigned int len); static inline void *__skb_pull(struct sk_buff *skb, unsigned int len) { + DEBUG_NET_WARN_ON_ONCE(len > INT_MAX); + skb->len -= len; if (unlikely(skb->len < skb->data_len)) { #if defined(CONFIG_DEBUG_NET) @@ -2674,6 +2678,8 @@ void *__pskb_pull_tail(struct sk_buff *skb, int delta); static inline enum skb_drop_reason pskb_may_pull_reason(struct sk_buff *skb, unsigned int len) { + DEBUG_NET_WARN_ON_ONCE(len > INT_MAX); + if (likely(len <= skb_headlen(skb))) return SKB_NOT_DROPPED_YET;
syzbot managed to trigger following splat: BUG: KASAN: use-after-free in __skb_flow_dissect+0x4a3b/0x5e50 Read of size 1 at addr ffff888208a4000e by task a.out/2313 [..] __skb_flow_dissect+0x4a3b/0x5e50 __skb_get_hash+0xb4/0x400 ip_tunnel_xmit+0x77e/0x26f0 ipip_tunnel_xmit+0x298/0x410 .. Analysis shows that the skb has a valid ->head, but bogus ->data pointer. skb->data gets its bogus value via the neigh layer, which does: 1556 __skb_pull(skb, skb_network_offset(skb)); ... and the skb was already dodgy at this point: skb_network_offset(skb) returns a negative value due to an earlier overflow of skb->network_header (u16). __skb_pull thus "adjusts" skb->data by a huge offset, pointing outside skb->head area. Allow debug builds to splat when we try to pull/push more than INT_MAX bytes. After this, the syzkaller reproducer yields a more precise splat before the flow dissector attempts to read off skb->data memory: WARNING: CPU: 5 PID: 2313 at include/linux/skbuff.h:2653 neigh_connected_output+0x28e/0x400 ip_finish_output2+0xb25/0xed0 iptunnel_xmit+0x4ff/0x870 ipgre_xmit+0x78e/0xbb0 Signed-off-by: Florian Westphal <fw@strlen.de> --- A fix to prevent network_header overflow will follow shortly. include/linux/skbuff.h | 6 ++++++ 1 file changed, 6 insertions(+)