From: Eric Dumazet <eduma...@google.com>
Andrey Konovalov got crashes in __ip_options_echo() when a NULL skb->dst
is accessed.
ipv4_pktinfo_prepare() should not drop the dst if (evil) IP options
are present.
We could refine the test to the presence of ts_needtime or srr,
but IP options are not often used, so let's be conservative.
Thanks to syzkaller team for finding this bug.
Fixes: d826eb14ecef ("ipv4: PKTINFO doesnt need dst reference")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Reported-by: Andrey Konovalov <andreyk...@google.com>
---
net/ipv4/ip_sockglue.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index
8a4409dd390aac7fcb88383af1550a2f967d..c4fcf9d713cca64a3afaec1628692739d9fa
100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -1243,7 +1243,14 @@ void ipv4_pktinfo_prepare(const struct sock *sk, struct
sk_buff *skb)
pktinfo->ipi_ifindex = 0;
pktinfo->ipi_spec_dst.s_addr = 0;
}
- skb_dst_drop(skb);
+ /* We need to keep the dst for __ip_options_echo()
+ * We could restrict the test to opt.ts_needtime || opt.srr,
+ * but the following is good enough as IP options are not often used.
+ */
+ if (unlikely(IPCB(skb)->opt.optlen))
+ skb_dst_force(skb);
+ else
+ skb_dst_drop(skb);
}
int ip_setsockopt(struct sock *sk, int level,
