bpf: skip unnecessary capability check

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@google.com>
Acked-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e24aa32..43f95d1 100644 (file)
--- 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);