From: Jann Horn <jannh@google.com>
Date: Mon, 18 Dec 2017 20:11:57 -0800
Subject: bpf: fix missing error return in check_stack_boundary()
Patch-mainline: v4.15-rc5
Git-commit: ea25f914dc164c8d56b36147ecc86bc65f83c469
References: CVE-2017-17857 bsc#1056787 bsc#1073928

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@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>

---
 kernel/bpf/verifier.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c832d31f1767..3d85d5ad33e8 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1340,6 +1340,7 @@ 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 ||
-- 
2.15.1