netdev - [PATCH bpf] bpf: respect CAP_IPC_LOCK in RLIMIT

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Message-Id: <20190911181816.89874-1-christian@cbarcenas.com>
Date:   Wed, 11 Sep 2019 11:18:16 -0700
From:   Christian Barcenas <christian@...rcenas.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org
Cc:     Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        Yonghong Song <yhs@...com>,
        Christian Barcenas <christian@...rcenas.com>,
        bpf@...r.kernel.org
Subject: [PATCH bpf] bpf: respect CAP_IPC_LOCK in RLIMIT_MEMLOCK check

A process can lock memory addresses into physical RAM explicitly
(via mlock, mlockall, shmctl, etc.) or implicitly (via VFIO,
perf ring-buffers, bpf maps, etc.), subject to RLIMIT_MEMLOCK limits.

CAP_IPC_LOCK allows a process to exceed these limits, and throughout
the kernel this capability is checked before allowing/denying an attempt
to lock memory regions into RAM.

Because bpf locks its programs and maps into RAM, it should respect
CAP_IPC_LOCK. Previously, bpf would return EPERM when RLIMIT_MEMLOCK was
exceeded by a privileged process, which is contrary to documented
RLIMIT_MEMLOCK+CAP_IPC_LOCK behavior.

Fixes: aaac3ba95e4c ("bpf: charge user for creation of BPF maps and programs")
Signed-off-by: Christian Barcenas <christian@...rcenas.com>
---
 kernel/bpf/syscall.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 272071e9112f..e551961f364b 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -183,8 +183,9 @@ void bpf_map_init_from_attr(struct bpf_map *map, union bpf_attr *attr)
 static int bpf_charge_memlock(struct user_struct *user, u32 pages)
 {
 	unsigned long memlock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+	unsigned long locked = atomic_long_add_return(pages, &user->locked_vm);
 
-	if (atomic_long_add_return(pages, &user->locked_vm) > memlock_limit) {
+	if (locked > memlock_limit && !capable(CAP_IPC_LOCK)) {
 		atomic_long_sub(pages, &user->locked_vm);
 		return -EPERM;
 	}
@@ -1231,7 +1232,7 @@ int __bpf_prog_charge(struct user_struct *user, u32 pages)
 
 	if (user) {
 		user_bufs = atomic_long_add_return(pages, &user->locked_vm);
-		if (user_bufs > memlock_limit) {
+		if (user_bufs > memlock_limit && !capable(CAP_IPC_LOCK)) {
 			atomic_long_sub(pages, &user->locked_vm);
 			return -EPERM;
 		}
-- 
2.23.0