From: Alexei Starovoitov <ast@kernel.org>
Date: Wed, 12 Sep 2018 21:06:10 +0000 (-0700)
Subject: bpf/verifier: disallow pointer subtraction
X-Git-Tag: v4.18.11~35
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=bc35488686c34703e5f0909c7a6cb0b942bfcf58;p=users%2Fdwmw2%2Flinux.git

bpf/verifier: disallow pointer subtraction

commit dd066823db2ac4e22f721ec85190817b58059a54 upstream.

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 <jannh@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 63aaac52a2655..adbe21c8876e0 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3132,7 +3132,7 @@ 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;
 				}