netdev - [PATCH bpf-next] bpf: skip unnecessary capability check

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Message-Id: <20180320005727.197544-1-chenbofeng.kernel@gmail.com>
Date:   Mon, 19 Mar 2018 17:57:27 -0700
From:   Chenbo Feng <chenbofeng.kernel@...il.com>
To:     netdev@...r.kernel.org, ast@...nel.org
Cc:     Jeffrey Vander Stoep <jeffv@...gle.com>, lorenzo@...gle.com,
        Daniel Borkmann <daniel@...earbox.net>,
        Chenbo Feng <fengc@...gle.com>
Subject: [PATCH bpf-next] bpf: skip unnecessary capability check

From: Chenbo Feng <fengc@...gle.com>

The current check statement in BPF syscall will do a capability check
for CAP_SYS_ADMIN before checking sysctl_unprivileged_bpf_disabled. This
code path will trigger unnecessary security hooks on capability checking
and cause false alarms on unprivileged process trying to get CAP_SYS_ADMIN
access. This can be resolved by simply switch the order of the statement
and CAP_SYS_ADMIN is not required anyway if unprivileged bpf syscall is
allowed.

Signed-off-by: Chenbo Feng <fengc@...gle.com>
---
 kernel/bpf/syscall.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e24aa3241387..43f95d190eea 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1845,7 +1845,7 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
 	union bpf_attr attr = {};
 	int err;
 
-	if (!capable(CAP_SYS_ADMIN) && sysctl_unprivileged_bpf_disabled)
+	if (sysctl_unprivileged_bpf_disabled && !capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
 	err = check_uarg_tail_zero(uattr, sizeof(attr), size);
-- 
2.16.2.804.g6dcf76e118-goog