linux-kernel - [PATCH] seccomp: allow BPF

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Date:   Fri, 9 Aug 2019 20:26:22 +0200
From:   Paul Chaignon <paul.chaignon@...nge.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] seccomp: allow BPF_MOD ALU instructions

We need BPF_MOD to match system calls against whitelists encoded as 32-bit
bit arrays.  The selection of the syscall's bit in the appropriate bit
array requires a modulo operation such that X = 1 << nr % 32.

Signed-off-by: Paul Chaignon <paul.chaignon@...nge.com>
---
 kernel/seccomp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 811b4a86cdf6..87de6532ff6d 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -205,6 +205,8 @@ static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
 		case BPF_ALU | BPF_MUL | BPF_X:
 		case BPF_ALU | BPF_DIV | BPF_K:
 		case BPF_ALU | BPF_DIV | BPF_X:
+		case BPF_ALU | BPF_MOD | BPF_K:
+		case BPF_ALU | BPF_MOD | BPF_X:
 		case BPF_ALU | BPF_AND | BPF_K:
 		case BPF_ALU | BPF_AND | BPF_X:
 		case BPF_ALU | BPF_OR | BPF_K:
-- 
2.17.1