From c09be31461ed140976c60a87364415454a2c3d42 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 17 May 2019 17:17:22 -0700 Subject: tcp: limit payload size of sacked skbs commit 3b4929f65b0d8249f19a50245cd88ed1a2f78cff upstream. 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 Reported-by: Jonathan Looney Acked-by: Neal Cardwell Reviewed-by: Tyler Hicks Cc: Yuchung Cheng Cc: Bruce Curtis Cc: Jonathan Lemon Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/linux/tcp.h | 4 ++++ include/net/tcp.h | 2 ++ 2 files changed, 6 insertions(+) (limited to 'include') diff --git a/include/linux/tcp.h b/include/linux/tcp.h index d2c8f280e48f..4374196b98ea 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -485,4 +485,8 @@ 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 770917d0caa7..e75661f92daa 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -55,6 +55,8 @@ 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 -- cgit v1.2.3