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Subject[PATCH 4.14 37/47] bpf/verifier: disallow pointer subtraction
Date
From: Alexei Starovoitov <ast@kernel.org>

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>
[fllinden@amazon.com: backport to 4.14]
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/bpf/verifier.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2754,7 +2754,7 @@ static int adjust_reg_min_max_vals(struc
* an arbitrary scalar. Disallow all math except
* pointer subtraction
*/
- if (opcode == BPF_SUB){
+ if (opcode == BPF_SUB && env->allow_ptr_leaks) {
mark_reg_unknown(regs, insn->dst_reg);
return 0;
}

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