Description
In the Linux kernel, the following vulnerability has been resolved: tcp: do not let tcp_rmem be set below 4096 We can hit a division by zero crash in tcp_rcvbuf_grow() and tcp_rcv_space_adjust(): divide error: 0000 [#1] PREEMPT SMP RIP: 0010:tcp_rcvbuf_grow+0x187/0x450 net/ipv4/tcp_input.c:939 ... grow = div_u64(((u64)rcvwin << 1) * (newval - oldval), oldval); The division uses oldval = tp->rcvq_space.space as divisor. When tp->rcvq_space.space is zero, this leads to a divide-by-zero exception. tp->rcvq_space.space is initialized in tcp_init_buffer_space(): tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd, (u32)TCP_INIT_CWND * tp->advmss); If tcp_rmem[1] is configured to very small values (such as 1), sk->sk_rcvbuf is initialized to 1. Then tcp_full_space(sk), which computes (sk->sk_rcvbuf * scaling_ratio) >> 8, truncates to 0. This sets tp->window_clamp = 0, tp->rcv_ssthresh = 0, and tp->rcvq_space.space = 0. Later, when data arrives and DRS is invoked, tcp_rcvbuf_grow() divides by oldval == 0. Back in 2015, commit b1cb59cf2efe ("net: sysctl_net_core: check SNDBUF and RCVBUF for min length") ensured that net.core.rmem_default and net.core.rmem_max cannot be set below SOCK_MIN_RCVBUF. Similarly, SO_RCVBUF setsockopt enforces max_t(int, val * 2, SOCK_MIN_RCVBUF). However, net.ipv4.tcp_rmem still had .extra1 = SYSCTL_ONE, allowing arbitrarily small values. Because SOCK_MIN_RCVBUF depends on sizeof(struct sk_buff) and cacheline alignment, its value varies across architectures and configuration options. Using a fixed constant of 4096 ensures a predictable, architecture- independent lower bound that is safely above SOCK_MIN_RCVBUF everywhere and matches the documented 4K default. Fix this by setting tcp_rmem.extra1 to 4096 and updating the documentation.
Affected products
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
Linux Linux
Default version status: unaffected
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 879907631b9e70eedb62d76461b29afa106ebe7aaffected1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 8e32532d0fa3191ecf9524b0e6bafa0832e712baaffected1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 67b83c15bed9eeeb8d1a6dbf88a5f79525970173affected1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 9a4f49bf8d2da4e52e904f60c29cca317bab9b3aaffected1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 60df201dbb19a1bf6478b56d100f7ae1fe90e46aaffected1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 7898bda1ebc198f5559b301a96dd5398edd4d4d3affected1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 1c4bb940c3bb4325bb88ac1b7eaf5faaa39e7d63affected1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 83a945a529d6e002dd7339c532288a931f463dbaaffected
Linux Linux
Default version status: affected
2.6.12affected0 to < 2.6.12unaffected5.10.271 to ≤ 5.10.*unaffected5.15.222 to ≤ 5.15.*unaffected6.1.189 to ≤ 6.1.*unaffected6.6.158 to ≤ 6.6.*unaffected6.12.112 to ≤ 6.12.*unaffected6.18.54 to ≤ 6.18.*unaffected7.2.8 to ≤ 7.2.*unaffected7.3 to ≤ *unaffected
References
- https://git.kernel.org/stable/c/879907631b9e70eedb62d76461b29afa106ebe7a ↗
- https://git.kernel.org/stable/c/8e32532d0fa3191ecf9524b0e6bafa0832e712ba ↗
- https://git.kernel.org/stable/c/67b83c15bed9eeeb8d1a6dbf88a5f79525970173 ↗
- https://git.kernel.org/stable/c/9a4f49bf8d2da4e52e904f60c29cca317bab9b3a ↗
- https://git.kernel.org/stable/c/60df201dbb19a1bf6478b56d100f7ae1fe90e46a ↗
- https://git.kernel.org/stable/c/7898bda1ebc198f5559b301a96dd5398edd4d4d3 ↗
- https://git.kernel.org/stable/c/1c4bb940c3bb4325bb88ac1b7eaf5faaa39e7d63 ↗
- https://git.kernel.org/stable/c/83a945a529d6e002dd7339c532288a931f463dba ↗