linux-kernel - [PATCH bpf-next] bpf: Remove unnecessary CAP_MAC

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Message-Id: <20200305204955.31123-1-kpsingh@chromium.org>
Date:   Thu,  5 Mar 2020 21:49:55 +0100
From:   KP Singh <kpsingh@...omium.org>
To:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Paul Turner <pjt@...gle.com>, Jann Horn <jannh@...gle.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>
Subject: [PATCH bpf-next] bpf: Remove unnecessary CAP_MAC_ADMIN check

From: KP Singh <kpsingh@...gle.com>

While well intentioned, checking CAP_MAC_ADMIN for attaching
BPF_MODIFY_RETURN tracing programs to "security_" functions is not
necessary as tracing BPF programs already require CAP_SYS_ADMIN.

Fixes: 6ba43b761c41 ("bpf: Attachment verification for BPF_MODIFY_RETURN")
Signed-off-by: KP Singh <kpsingh@...gle.com>
---
 kernel/bpf/verifier.c | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ae32517d4ccd..55d376c53f7d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9808,20 +9808,13 @@ static int check_attach_modify_return(struct bpf_verifier_env *env)
 	struct bpf_prog *prog = env->prog;
 	unsigned long addr = (unsigned long) prog->aux->trampoline->func.addr;
 
-	if (within_error_injection_list(addr))
-		return 0;
-
 	/* This is expected to be cleaned up in the future with the KRSI effort
 	 * introducing the LSM_HOOK macro for cleaning up lsm_hooks.h.
 	 */
-	if (!strncmp(SECURITY_PREFIX, prog->aux->attach_func_name,
-		     sizeof(SECURITY_PREFIX) - 1)) {
-
-		if (!capable(CAP_MAC_ADMIN))
-			return -EPERM;
-
+	if (within_error_injection_list(addr) ||
+	    !strncmp(SECURITY_PREFIX, prog->aux->attach_func_name,
+		     sizeof(SECURITY_PREFIX) - 1))
 		return 0;
-	}
 
 	verbose(env, "fmod_ret attach_btf_id %u (%s) is not modifiable\n",
 		prog->aux->attach_btf_id, prog->aux->attach_func_name);
-- 
2.20.1