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authorEric Dumazet <edumazet@google.com>2019-05-17 17:17:22 -0700
committerDavid S. Miller <davem@davemloft.net>2019-06-15 18:47:31 -0700
commit3b4929f65b0d8249f19a50245cd88ed1a2f78cff (patch)
tree6f48603df7001f7048016a2e98573bf10044dd3e /include
parent1eb4169c1e6b3c95f3a99c2c7f91b10e6c98e848 (diff)
tcp: limit payload size of sacked skbs
Jonathan Looney reported that TCP can trigger the following crash in tcp_shifted_skb() : BUG_ON(tcp_skb_pcount(skb) < pcount); This can happen if the remote peer has advertized the smallest MSS that linux TCP accepts : 48 An skb can hold 17 fragments, and each fragment can hold 32KB on x86, or 64KB on PowerPC. This means that the 16bit witdh of TCP_SKB_CB(skb)->tcp_gso_segs can overflow. Note that tcp_sendmsg() builds skbs with less than 64KB of payload, so this problem needs SACK to be enabled. SACK blocks allow TCP to coalesce multiple skbs in the retransmit queue, thus filling the 17 fragments to maximal capacity. CVE-2019-11477 -- u16 overflow of TCP_SKB_CB(skb)->tcp_gso_segs Fixes: 832d11c5cd07 ("tcp: Try to restore large SKBs while SACK processing") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Jonathan Looney <jtl@netflix.com> Acked-by: Neal Cardwell <ncardwell@google.com> Reviewed-by: Tyler Hicks <tyhicks@canonical.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Bruce Curtis <brucec@netflix.com> Cc: Jonathan Lemon <jonathan.lemon@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include')
-rw-r--r--include/linux/tcp.h4
-rw-r--r--include/net/tcp.h2
2 files changed, 6 insertions, 0 deletions
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 711361af9ce0..9a478a0cd3a2 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -484,4 +484,8 @@ static inline u16 tcp_mss_clamp(const struct tcp_sock *tp, u16 mss)
return (user_mss && user_mss < mss) ? user_mss : mss;
}
+
+int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from, int pcount,
+ int shiftlen);
+
#endif /* _LINUX_TCP_H */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index ac2f53fbfa6b..582c0caa9811 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -51,6 +51,8 @@ void tcp_time_wait(struct sock *sk, int state, int timeo);
#define MAX_TCP_HEADER (128 + MAX_HEADER)
#define MAX_TCP_OPTION_SPACE 40
+#define TCP_MIN_SND_MSS 48
+#define TCP_MIN_GSO_SIZE (TCP_MIN_SND_MSS - MAX_TCP_OPTION_SPACE)
/*
* Never offer a window over 32767 without using window scaling. Some