linux-kernel - [PATCH net] net: fix crash when config small gso_max_size/gso_ipv4_max

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Message-ID: <20241022085759.1328477-1-wangliang74@huawei.com>
Date: Tue, 22 Oct 2024 16:57:59 +0800
From: Wang Liang <wangliang74@...wei.com>
To: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <idosch@...dia.com>, <kuniyu@...zon.com>,
	<stephen@...workplumber.org>, <dsahern@...nel.org>, <lucien.xin@...il.com>
CC: <wangliang74@...wei.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH net] net: fix crash when config small gso_max_size/gso_ipv4_max_size

Config a small gso_max_size/gso_ipv4_max_size can lead to large skb len,
which may trigger a BUG_ON crash.

If the gso_max_size/gso_ipv4_max_size is smaller than MAX_TCP_HEADER + 1,
the sk->sk_gso_max_size is overflowed:
sk_setup_caps
    // dst->dev->gso_ipv4_max_size = 252, MAX_TCP_HEADER = 320
    // GSO_LEGACY_MAX_SIZE = 65536, sk_is_tcp(sk) = 1
    sk->sk_gso_max_size = sk_dst_gso_max_size(sk, dst);
        max_size = dst->dev->gso_ipv4_max_size;
            sk->sk_gso_max_size = max_size - (MAX_TCP_HEADER + 1);
            sk->sk_gso_max_size = 252-(320+1) = -69

When send tcp msg, the wrong sk_gso_max_size can lead to a very large
size_goal, which cause large skb length:
tcp_sendmsg_locked
    tcp_send_mss(sk, &size_goal, flags);
        tcp_xmit_size_goal(sk, mss_now, !(flags & MSG_OOB));

            // tp->max_window = 65536, TCP_MSS_DEFAULT = 536
            new_size_goal = tcp_bound_to_half_wnd(tp, sk->sk_gso_max_size);
                new_size_goal = sk->sk_gso_max_size = -69

            // tp->gso_segs = 0, mss_now = 32768
            size_goal = tp->gso_segs * mss_now;
                size_goal = 0*32768 = 0

            // sk->sk_gso_max_segs = 65535, new_size_goal = -69
            new_size_goal < size_goal:
                tp->gso_segs = min_t(u16, new_size_goal / mss_now,
                     sk->sk_gso_max_segs);
                // new_size_goal / mss_now = 0x1FFFF -> 65535
                // tp->gso_segs = 65535
                size_goal = tp->gso_segs * mss_now;
                size_goal = 65535*32768 = 2147450880

    if new_segment:
        skb = tcp_stream_alloc_skb()
        copy = size_goal; // copy = 2147450880
    if (copy > msg_data_left(msg)) // msg_data_left(msg) = 2147479552
        copy = msg_data_left(msg); // copy = 2147450880
    copy = min_t(int, copy, pfrag->size - pfrag->offset); // copy = 21360
    skb_copy_to_page_nocache
        skb_len_add
            skb->len += copy; // skb->len add to 524288

The large skb length may load to a overflowed tso_segs, which can trigger
a BUG_ON crash:
tcp_write_xmit
    tso_segs = tcp_init_tso_segs(skb, mss_now);
        tcp_set_skb_tso_segs
            tcp_skb_pcount_set
                // skb->len = 524288, mss_now = 8
                // u16 tso_segs = 524288/8 = 65535 -> 0
                tso_segs = DIV_ROUND_UP(skb->len, mss_now)
    BUG_ON(!tso_segs)

To solve this issue, the minimum value of gso_max_size/gso_ipv4_max_size
should be checked.

Fixes: 46e6b992c250 ("rtnetlink: allow GSO maximums to be set on device creation")
Fixes: 9eefedd58ae1 ("net: add gso_ipv4_max_size and gro_ipv4_max_size per device")
Signed-off-by: Wang Liang <wangliang74@...wei.com>
---
 net/core/rtnetlink.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index e30e7ea0207d..a0df1da5a0a6 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -2466,6 +2466,12 @@ static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[],
 		return -EINVAL;
 	}
 
+	if (tb[IFLA_GSO_MAX_SIZE] &&
+	    (nla_get_u32(tb[IFLA_GSO_MAX_SIZE]) < MAX_TCP_HEADER + 1)) {
+		NL_SET_ERR_MSG(extack, "too small gso_max_size");
+		return -EINVAL;
+	}
+
 	if (tb[IFLA_GSO_MAX_SEGS] &&
 	    (nla_get_u32(tb[IFLA_GSO_MAX_SEGS]) > GSO_MAX_SEGS ||
 	     nla_get_u32(tb[IFLA_GSO_MAX_SEGS]) > dev->tso_max_segs)) {
@@ -2485,6 +2491,12 @@ static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[],
 		return -EINVAL;
 	}
 
+	if (tb[IFLA_GSO_IPV4_MAX_SIZE] &&
+	    (nla_get_u32(tb[IFLA_GSO_IPV4_MAX_SIZE]) < MAX_TCP_HEADER + 1)) {
+		NL_SET_ERR_MSG(extack, "too small gso_ipv4_max_size");
+		return -EINVAL;
+	}
+
 	if (tb[IFLA_GRO_IPV4_MAX_SIZE] &&
 	    nla_get_u32(tb[IFLA_GRO_IPV4_MAX_SIZE]) > GRO_MAX_SIZE) {
 		NL_SET_ERR_MSG(extack, "too big gro_ipv4_max_size");
-- 
2.34.1