[PATCH] bpf, mips: fix off-by-one in ctx offset allocation

[PATCH] bpf, mips: fix off-by-one in ctx offset allocation

[Daniel Borkmann]

Dan Carpenter reported [1] a static checker warning that ctx->offsets[]
may be accessed off by one from build_body(), since it's allocated with
fp->len * sizeof(*ctx.offsets) as length. The cBPF arm and ppc code
doesn't have this issue as claimed, so only mips seems to be affected and
should like most other JITs allocate with fp->len + 1. A few number of
JITs (x86, sparc, arm64) handle this differently, where they only require
fp->len array elements.

  [1] http://www.spinics.net/lists/mips/msg64193.html

Fixes: c6610de353da ("MIPS: net: Add BPF JIT")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: linux-mips@linux-mips.org
---
 arch/mips/net/bpf_jit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c
index 1a8c960..a04c393 100644
--- a/arch/mips/net/bpf_jit.c
+++ b/arch/mips/net/bpf_jit.c
@@ -1199,7 +1199,7 @@ void bpf_jit_compile(struct bpf_prog *fp)
 
 	memset(&ctx, 0, sizeof(ctx));
 
-	ctx.offsets = kcalloc(fp->len, sizeof(*ctx.offsets), GFP_KERNEL);
+	ctx.offsets = kcalloc(fp->len + 1, sizeof(*ctx.offsets), GFP_KERNEL);
 	if (ctx.offsets == NULL)
 		return;
 
-- 
1.9.3

Re: [PATCH] bpf, mips: fix off-by-one in ctx offset allocation

[Dan Carpenter]

On Thu, Jul 14, 2016 at 01:57:55PM +0200, Daniel Borkmann wrote:
> The cBPF arm and ppc code doesn't have this issue as claimed

Oh, yeah.  You're correct, obviously.  I didn't look carefully.

regards,
dan carpenter