linux-kernel - [PATCH 4.4 42/43] bpf: skip unnecessary capability check

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Date:   Tue, 27 Mar 2018 18:27:46 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Chenbo Feng <fengc@...gle.com>,
        Lorenzo Colitti <lorenzo@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH 4.4 42/43] bpf: skip unnecessary capability check

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit 0fa4fe85f4724fff89b09741c437cbee9cf8b008 upstream.

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>
Acked-by: Lorenzo Colitti <lorenzo@...gle.com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/bpf/syscall.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -673,7 +673,7 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf
 	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;

 	if (!access_ok(VERIFY_READ, uattr, 1))