From cd2f6cfd37d4125a7b84c10fb620ffbe7f2c815b Mon Sep 17 00:00:00 2001 From: Stanislav Fomichev Date: Thu, 11 May 2023 10:04:53 -0700 Subject: [PATCH] bpf: Don't EFAULT for {g,s}setsockopt with wrong optlen [ Upstream commit 29ebbba7d46136cba324264e513a1e964ca16c0a ] With the way the hooks implemented right now, we have a special condition: optval larger than PAGE_SIZE will expose only first 4k into BPF; any modifications to the optval are ignored. If the BPF program doesn't handle this condition by resetting optlen to 0, the userspace will get EFAULT. The intention of the EFAULT was to make it apparent to the developers that the program is doing something wrong. However, this inadvertently might affect production workloads with the BPF programs that are not too careful (i.e., returning EFAULT for perfectly valid setsockopt/getsockopt calls). Let's try to minimize the chance of BPF program screwing up userspace by ignoring the output of those BPF programs (instead of returning EFAULT to the userspace). pr_info_once those cases to the dmesg to help with figuring out what's going wrong. Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks") Suggested-by: Martin KaFai Lau Signed-off-by: Stanislav Fomichev Link: https://lore.kernel.org/r/20230511170456.1759459-2-sdf@google.com Signed-off-by: Martin KaFai Lau Signed-off-by: Sasha Levin --- kernel/bpf/cgroup.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index 87174832aa86..297569e5c639 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -1481,6 +1481,12 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level, ret = 1; } else if (ctx.optlen > max_optlen || ctx.optlen < -1) { /* optlen is out of bounds */ + if (*optlen > PAGE_SIZE && ctx.optlen >= 0) { + pr_info_once("bpf setsockopt: ignoring program buffer with optlen=%d (max_optlen=%d)\n", + ctx.optlen, max_optlen); + ret = 0; + goto out; + } ret = -EFAULT; } else { /* optlen within bounds, run kernel handler */ @@ -1536,6 +1542,7 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level, .optname = optname, .retval = retval, }; + int orig_optlen; int ret; /* Opportunistic check to see whether we have any BPF program @@ -1545,6 +1552,7 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level, if (__cgroup_bpf_prog_array_is_empty(cgrp, CGROUP_GETSOCKOPT)) return retval; + orig_optlen = max_optlen; ctx.optlen = max_optlen; max_optlen = sockopt_alloc_buf(&ctx, max_optlen, &buf); @@ -1568,6 +1576,7 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level, ret = -EFAULT; goto out; } + orig_optlen = ctx.optlen; if (copy_from_user(ctx.optval, optval, min(ctx.optlen, max_optlen)) != 0) { @@ -1587,6 +1596,12 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level, } if (optval && (ctx.optlen > max_optlen || ctx.optlen < 0)) { + if (orig_optlen > PAGE_SIZE && ctx.optlen >= 0) { + pr_info_once("bpf getsockopt: ignoring program buffer with optlen=%d (max_optlen=%d)\n", + ctx.optlen, max_optlen); + ret = retval; + goto out; + } ret = -EFAULT; goto out; }