commit dd066823db2ac4e22f721ec85190817b58059a54
author Alexei Starovoitov <ast@kernel.org> Wed Sep 12 14:06:10 2018 -0700
committer Daniel Borkmann <daniel@iogearbox.net> Wed Sep 12 23:30:02 2018 +0200
tree f7f40317bb1474a382035fb58a120e73c82fec46
parent 4b1c5d917d34f705096bb7dd8a2bd19b0881970e

bpf/verifier: disallow pointer subtraction

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>

kernel/bpf/verifier.c

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9224611..bb07e74 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;
 				}