In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
tcp: do not let tcp_rmem be set below 4096<\/p>\n
We can hit a division by zero crash in tcp_rcvbuf_grow()
\nand tcp_rcv_space_adjust():<\/p>\n
divide error: 0000 [#1] PREEMPT SMP
\nRIP: 0010:tcp_rcvbuf_grow+0x187\/0x450 net\/ipv4\/tcp_input.c:939
\n…
\ngrow = div_u64(((u64)rcvwin <rcvq_space.space as divisor.
\nWhen tp->rcvq_space.space is zero, this leads to a divide-by-zero
\nexception.<\/p>\n
tp->rcvq_space.space is initialized in tcp_init_buffer_space():
\n tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd,
\n (u32)TCP_INIT_CWND * tp->advmss);<\/p>\n
If tcp_rmem[1] is configured to very small values (such as 1),
\nsk->sk_rcvbuf is initialized to 1. Then tcp_full_space(sk), which
\ncomputes (sk->sk_rcvbuf * scaling_ratio) >> 8, truncates to 0.
\nThis sets tp->window_clamp = 0, tp->rcv_ssthresh = 0, and
\ntp->rcvq_space.space = 0. Later, when data arrives and DRS is invoked,
\ntcp_rcvbuf_grow() divides by oldval == 0.<\/p>\n
Back in 2015, commit b1cb59cf2efe (“net: sysctl_net_core: check SNDBUF
\nand RCVBUF for min length”) ensured that net.core.rmem_default and
\nnet.core.rmem_max cannot be set below SOCK_MIN_RCVBUF. Similarly,
\nSO_RCVBUF setsockopt enforces max_t(int, val * 2, SOCK_MIN_RCVBUF).<\/p>\n
However, net.ipv4.tcp_rmem still had .extra1 = SYSCTL_ONE, allowing
\narbitrarily small values.<\/p>\n
Because SOCK_MIN_RCVBUF depends on sizeof(struct sk_buff) and cacheline
\nalignment, its value varies across architectures and configuration options.
\nUsing a fixed constant of 4096 ensures a predictable, architecture-
\nindependent lower bound that is safely above SOCK_MIN_RCVBUF everywhere
\nand matches the documented 4K default.<\/p>\n
Fix this by setting tcp_rmem.extra1 to 4096 and updating the documentation.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
tcp: do not let tcp_rmem be set below 4096<\/p>\n
We can hit a division by zero crash in tcp_rcvbuf_grow()
\nand tcp_rcv_space_adjust():<\/p>\n
d<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-33368","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/33368","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=33368"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=33368"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=33368"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}