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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Peter Robinson <pbrobinson@gmail.com>,
        Marc Haber <mh+netdev@zugschlus.de>,
        Stefan Wahren <stefan.wahren@i2se.com>,
        Russell King <rmk+kernel@armlinux.org.uk>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>
Subject: [PATCH 4.18 022/123] bpf, arm32: fix stack var offset in jit
Date:   Mon,  3 Sep 2018 18:56:06 +0200
Message-Id: <20180903165720.438298034@linuxfoundation.org>
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4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Borkmann <daniel@iogearbox.net>

Commit 38ca93060163 ("bpf, arm32: save 4 bytes of unneeded stack
space") messed up STACK_VAR() by 4 bytes presuming it was related
to skb scratch buffer space, but it clearly isn't as this refers
to the top word in stack, therefore restore it. This fixes a NULL
pointer dereference seen during bootup when JIT is enabled and BPF
program run in sk_filter_trim_cap() triggered by systemd-udevd.

JIT rework in 1c35ba122d4a ("ARM: net: bpf: use negative numbers
for stacked registers") and 96cced4e774a ("ARM: net: bpf: access
eBPF scratch space using ARM FP register") removed the affected
parts, so only needed in 4.18 stable.

Fixes: 38ca93060163 ("bpf, arm32: save 4 bytes of unneeded stack space")
Reported-by: Peter Robinson <pbrobinson@gmail.com>
Reported-by: Marc Haber <mh+netdev@zugschlus.de>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Tested-by: Peter Robinson <pbrobinson@gmail.com>
Cc: Russell King <rmk+kernel@armlinux.org.uk>
Cc: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
 arch/arm/net/bpf_jit_32.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -238,7 +238,7 @@ static void jit_fill_hole(void *area, un
 #define STACK_SIZE	ALIGN(_STACK_SIZE, STACK_ALIGNMENT)
 
 /* Get the offset of eBPF REGISTERs stored on scratch space. */
-#define STACK_VAR(off) (STACK_SIZE - off)
+#define STACK_VAR(off) (STACK_SIZE - off - 4)
 
 #if __LINUX_ARM_ARCH__ < 7