[PATCH bpf-next 1/4] bpf: move unprivileged checks into map_create() and bpf_prog_load()

[Andrii Nakryiko <andrii@kernel.org>]

Make each bpf() syscall command a bit more self-contained, making it
easier to further enhance it. We move sysctl_unprivileged_bpf_disabled
handling down to map_create() and bpf_prog_load(), two special commands
in this regard.

Also swap the order of checks, calling bpf_capable() only if
sysctl_unprivileged_bpf_disabled is true, avoiding unnecessary audit
messages.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 kernel/bpf/syscall.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 92a57efc77de..1cc590101e19 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1157,6 +1157,15 @@ static int map_create(union bpf_attr *attr)
 	     !node_online(numa_node)))
 		return -EINVAL;
 
+	/* Intent here is for unprivileged_bpf_disabled to block BPF map
+	 * creation for unprivileged users; other actions depend
+	 * on fd availability and access to bpffs, so are dependent on
+	 * object creation success. Even with unprivileged BPF disabled,
+	 * capability checks are still carried out.
+	 */
+	if (sysctl_unprivileged_bpf_disabled && !bpf_capable())
+		return -EPERM;
+
 	/* find map type and init map: hashtable vs rbtree vs bloom vs ... */
 	map = find_and_alloc_map(attr);
 	if (IS_ERR(map))
@@ -2532,6 +2541,16 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
 	/* eBPF programs must be GPL compatible to use GPL-ed functions */
 	is_gpl = license_is_gpl_compatible(license);
 
+	/* Intent here is for unprivileged_bpf_disabled to block BPF program
+	 * creation for unprivileged users; other actions depend
+	 * on fd availability and access to bpffs, so are dependent on
+	 * object creation success. Even with unprivileged BPF disabled,
+	 * capability checks are still carried out for these
+	 * and other operations.
+	 */
+	if (sysctl_unprivileged_bpf_disabled && !bpf_capable())
+		return -EPERM;
+
 	if (attr->insn_cnt == 0 ||
 	    attr->insn_cnt > (bpf_capable() ? BPF_COMPLEXITY_LIMIT_INSNS : BPF_MAXINSNS))
 		return -E2BIG;
@@ -5027,23 +5046,8 @@ static int bpf_prog_bind_map(union bpf_attr *attr)
 static int __sys_bpf(int cmd, bpfptr_t uattr, unsigned int size)
 {
 	union bpf_attr attr;
-	bool capable;
 	int err;
 
-	capable = bpf_capable() || !sysctl_unprivileged_bpf_disabled;
-
-	/* Intent here is for unprivileged_bpf_disabled to block key object
-	 * creation commands for unprivileged users; other actions depend
-	 * of fd availability and access to bpffs, so are dependent on
-	 * object creation success.  Capabilities are later verified for
-	 * operations such as load and map create, so even with unprivileged
-	 * BPF disabled, capability checks are still carried out for these
-	 * and other operations.
-	 */
-	if (!capable &&
-	    (cmd == BPF_MAP_CREATE || cmd == BPF_PROG_LOAD))
-		return -EPERM;
-
 	err = bpf_check_uarg_tail_zero(uattr, sizeof(attr), size);
 	if (err)
 		return err;
-- 
2.34.1