linux-kernel - [RFC PATCH stable 5.4 8/8] bpf: bpf_probe_read_kernel_str() has to return amount of data read on success

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Date:   Mon, 22 May 2023 22:33:52 +0200
From:   Jiri Olsa <jolsa@...nel.org>
To:     stable@...r.kernel.org
Cc:     Christoph Hellwig <hch@....de>,
        John Fastabend <john.fastabend@...il.com>, linux-mm@...ck.org,
        bpf@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tsahee Zidenberg <tsahee@...apurnalabs.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mahé Tardy <mahe.tardy@...valent.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: [RFC PATCH stable 5.4 8/8] bpf: bpf_probe_read_kernel_str() has to return amount of data read on success

From: Andrii Nakryiko <andriin@...com>

commit 02553b91da5deb63c8562b47529b09b734659af0 upstream.

During recent refactorings, bpf_probe_read_kernel_str() started returning 0 on
success, instead of amount of data successfully read. This majorly breaks
applications relying on bpf_probe_read_kernel_str() and bpf_probe_read_str()
and their results. Fix this by returning actual number of bytes read.

Fixes: 8d92db5c04d1 ("bpf: rework the compat kernel probe handling")
Signed-off-by: Andrii Nakryiko <andriin@...com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Reviewed-by: Christoph Hellwig <hch@....de>
Acked-by: John Fastabend <john.fastabend@...il.com>
Link: https://lore.kernel.org/bpf/20200616050432.1902042-1-andriin@fb.com
---
 kernel/trace/bpf_trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a46256f99229..c4c825dcdef8 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -198,7 +198,7 @@ bpf_probe_read_kernel_str_common(void *dst, u32 size, const void *unsafe_ptr)
 	if (unlikely(ret < 0))
 		goto fail;
 
-	return 0;
+	return ret;
 fail:
 	memset(dst, 0, size);
 	return ret;
-- 
2.40.1