netdev - [PATCH bpf 5/9] bpf: fix missing error return in check_stack

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Date:   Mon, 18 Dec 2017 20:11:57 -0800
From:   Alexei Starovoitov <ast@...nel.org>
To:     "David S . Miller" <davem@...emloft.net>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        Jann Horn <jannh@...gle.com>,
        Edward Cree <ecree@...arflare.com>, <netdev@...r.kernel.org>,
        <kernel-team@...com>
Subject: [PATCH bpf 5/9] bpf: fix missing error return in check_stack_boundary()

From: Jann Horn <jannh@...gle.com>

Prevent indirect stack accesses at non-constant addresses, which would
permit reading and corrupting spilled pointers.

Fixes: f1174f77b50c ("bpf/verifier: rework value tracking")
Signed-off-by: Jann Horn <jannh@...gle.com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
---
 kernel/bpf/verifier.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ecdc265244ca..77e4b5223867 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1303,6 +1303,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
 		tnum_strn(tn_buf, sizeof(tn_buf), regs[regno].var_off);
 		verbose(env, "invalid variable stack read R%d var_off=%s\n",
 			regno, tn_buf);
+		return -EACCES;
 	}
 	off = regs[regno].off + regs[regno].var_off.value;
 	if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 ||
-- 
2.9.5