From: Eric Dumazet Date: Sat, 18 May 2019 00:17:22 +0000 (-0700) Subject: tcp: limit payload size of sacked skbs X-Git-Tag: v4.19.52~4 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c09be31461ed140976c60a87364415454a2c3d42;p=platform%2Fkernel%2Flinux-rpi.git 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 --- diff --git a/include/linux/tcp.h b/include/linux/tcp.h index d2c8f28..4374196 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 770917d..e75661f 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 diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 30c6e94..364e6fd 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3829,6 +3829,7 @@ void __init tcp_init(void) unsigned long limit; unsigned int i; + BUILD_BUG_ON(TCP_MIN_SND_MSS <= MAX_TCP_OPTION_SPACE); BUILD_BUG_ON(sizeof(struct tcp_skb_cb) > FIELD_SIZEOF(struct sk_buff, cb)); diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index cfdd70e..4a8869d 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -1315,7 +1315,7 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev, TCP_SKB_CB(skb)->seq += shifted; tcp_skb_pcount_add(prev, pcount); - BUG_ON(tcp_skb_pcount(skb) < pcount); + WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount); tcp_skb_pcount_add(skb, -pcount); /* When we're adding to gso_segs == 1, gso_size will be zero, @@ -1381,6 +1381,21 @@ static int skb_can_shift(const struct sk_buff *skb) return !skb_headlen(skb) && skb_is_nonlinear(skb); } +int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from, + int pcount, int shiftlen) +{ + /* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE) + * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need + * to make sure not storing more than 65535 * 8 bytes per skb, + * even if current MSS is bigger. + */ + if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE)) + return 0; + if (unlikely(tcp_skb_pcount(to) + pcount > 65535)) + return 0; + return skb_shift(to, from, shiftlen); +} + /* Try collapsing SACK blocks spanning across multiple skbs to a single * skb. */ @@ -1486,7 +1501,7 @@ static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb, if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una)) goto fallback; - if (!skb_shift(prev, skb, len)) + if (!tcp_skb_shift(prev, skb, pcount, len)) goto fallback; if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack)) goto out; @@ -1504,11 +1519,10 @@ static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb, goto out; len = skb->len; - if (skb_shift(prev, skb, len)) { - pcount += tcp_skb_pcount(skb); - tcp_shifted_skb(sk, prev, skb, state, tcp_skb_pcount(skb), + pcount = tcp_skb_pcount(skb); + if (tcp_skb_shift(prev, skb, pcount, len)) + tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, 0); - } out: return prev; diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index bd134e3..c8a2960 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1457,8 +1457,8 @@ static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu) mss_now -= icsk->icsk_ext_hdr_len; /* Then reserve room for full set of TCP options and 8 bytes of data */ - if (mss_now < 48) - mss_now = 48; + if (mss_now < TCP_MIN_SND_MSS) + mss_now = TCP_MIN_SND_MSS; return mss_now; } @@ -2727,7 +2727,7 @@ static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb) if (next_skb_size <= skb_availroom(skb)) skb_copy_bits(next_skb, 0, skb_put(skb, next_skb_size), next_skb_size); - else if (!skb_shift(skb, next_skb, next_skb_size)) + else if (!tcp_skb_shift(skb, next_skb, 1, next_skb_size)) return false; } tcp_highest_sack_replace(sk, next_skb, skb);