From: Gianluca Borello <g.borello@gmail.com>
Date: Wed, 22 Nov 2017 18:32:54 +0000 (+0000)
Subject: bpf: remove explicit handling of 0 for arg2 in bpf_probe_read
X-Git-Tag: v4.19~2099^2~5^2~1^2~2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=eb33f2cca49ec49a1b893b5af546e7c042ca6365;p=platform%2Fkernel%2Flinux-rpi.git

bpf: remove explicit handling of 0 for arg2 in bpf_probe_read

Commit 9c019e2bc4b2 ("bpf: change helper bpf_probe_read arg2 type to
ARG_CONST_SIZE_OR_ZERO") changed arg2 type to ARG_CONST_SIZE_OR_ZERO to
simplify writing bpf programs by taking advantage of the new semantics
introduced for ARG_CONST_SIZE_OR_ZERO which allows <!NULL, 0> arguments.

In order to prevent the helper from actually passing a NULL pointer to
probe_kernel_read, which can happen when <NULL, 0> is passed to the helper,
the commit also introduced an explicit check against size == 0.

After the recent introduction of the ARG_PTR_TO_MEM_OR_NULL type,
bpf_probe_read can not receive a pair of <NULL, 0> arguments anymore, thus
the check is not needed anymore and can be removed, since probe_kernel_read
can correctly handle a <!NULL, 0> call. This also fixes the semantics of
the helper before it gets officially released and bpf programs start
relying on this check.

Fixes: 9c019e2bc4b2 ("bpf: change helper bpf_probe_read arg2 type to ARG_CONST_SIZE_OR_ZERO")
Signed-off-by: Gianluca Borello <g.borello@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a5580c670866..728909f7951c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -78,16 +78,12 @@ EXPORT_SYMBOL_GPL(trace_call_bpf);
 
 BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
 {
-	int ret = 0;
-
-	if (unlikely(size == 0))
-		goto out;
+	int ret;
 
 	ret = probe_kernel_read(dst, unsafe_ptr, size);
 	if (unlikely(ret < 0))
 		memset(dst, 0, size);
 
- out:
 	return ret;
 }