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

commit b4e76f7e upstream.

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: c6610de3 ("MIPS: net: Add BPF JIT")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: ast@kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13814/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/mips/net/bpf_jit.c

@@ -1365,7 +1365,7 @@ void bpf_jit_compile(struct sk_filter *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;