netdev - [PATCH] bpf: fix a bug in verification logic when SUB operation taken on FRAME

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <1434615176-96706-1-git-send-email-wangnan0@huawei.com>
Date:	Thu, 18 Jun 2015 08:12:56 +0000
From:	Wang Nan <wangnan0@...wei.com>
To:	<ast@...nel.org>
CC:	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<lizefan@...wei.com>
Subject: [PATCH] bpf: fix a bug in verification logic when SUB operation taken on FRAME_PTR

Original code has a problem, cause following code failed to pass verifier:

 r1 <- r10
 r1 -= 8
 r2 = 8
 r3 = unsafe pointer
 call BPF_FUNC_probe_read  <-- R1 type=inv expected=fp

However, by replacing 'r1 -= 8' to 'r1 += -8' the above program can be
loaded successfully.

This is because the verifier allows only BPF_ADD instruction on a
FRAME_PTR reigster to forge PTR_TO_STACK register, but makes BPF_SUB
on FRAME_PTR reigster to get a UNKNOWN_VALUE register.

This patch fix it by adding BPF_SUB in stack_relative checking.

Signed-off-by: Wang Nan <wangnan0@...wei.com>
---
 kernel/bpf/verifier.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a251cf6..6dbdeba 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1020,7 +1020,8 @@ static int check_alu_op(struct reg_state *regs, struct bpf_insn *insn)
 		}
 
 		/* pattern match 'bpf_add Rx, imm' instruction */
-		if (opcode == BPF_ADD && BPF_CLASS(insn->code) == BPF_ALU64 &&
+		if (opcode == BPF_ADD && opcode == BPF_SUB &&
+		    BPF_CLASS(insn->code) == BPF_ALU64 &&
 		    regs[insn->dst_reg].type == FRAME_PTR &&
 		    BPF_SRC(insn->code) == BPF_K)
 			stack_relative = true;
-- 
1.8.3.4

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html