[PATCH bpf] bpf/verifier: disallow pointer subtraction

[Alexei Starovoitov]

Subtraction of pointers was accidentally allowed for unpriv programs
by commit 82abbf8d2fc4. Revert that part of commit.

Fixes: 82abbf8d2fc4 ("bpf: do not allow root to mangle valid pointers")
Reported-by: Jann Horn <ja...@google.com>
Acked-by: Daniel Borkmann <dan...@iogearbox.net>
Signed-off-by: Alexei Starovoitov <a...@kernel.org>
---
 kernel/bpf/verifier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 92246117d2b0..bb07e74b34a2 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3163,7 +3163,7 @@ static int adjust_reg_min_max_vals(struct 
bpf_verifier_env *env,
                                 * an arbitrary scalar. Disallow all math except
                                 * pointer subtraction
                                 */
-                               if (opcode == BPF_SUB){
+                               if (opcode == BPF_SUB && env->allow_ptr_leaks) {
                                        mark_reg_unknown(env, regs, 
insn->dst_reg);
                                        return 0;
                                }
-- 
2.17.1