Commit f8f2077d authored Jul 04, 2024 by Stanislav Fomichev Committed by Zheng Yejian Jul 04, 2024

bpf: Don't EFAULT for {g,s}setsockopt with wrong optlen

mainline inclusion
from mainline-v6.5-rc1
commit 29ebbba7
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/IAAAW9

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=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: 0d01da6a ("bpf: implement getsockopt and setsockopt hooks")
Suggested-by: Martin KaFai Lau <martin.lau@kernel.org>
Conflicts:
	kernel/bpf/cgroup.c
[Resolve conflicts]
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20230511170456.1759459-2-sdf@google.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>

parent 6e1b2a17

kernel/bpf/cgroup.c

+15 −0

Original line number	Diff line number	Diff line
		@@ -1477,6 +1477,12 @@ 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 */
		@@ -1532,6 +1538,7 @@ 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
		@@ -1541,6 +1548,7 @@ 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);
		@@ -1564,6 +1572,7 @@ 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) {
		@@ -1583,6 +1592,12 @@ 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;
		}