netdev - [PATCH AUTOSEL 4.9 02/21] samples, bpf: fix to change the buffer size for read()

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Date:   Wed, 26 Jun 2019 20:41:02 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Chang-Hsien Tsai <luke.tw@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Sasha Levin <sashal@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 02/21] samples, bpf: fix to change the buffer size for read()

From: Chang-Hsien Tsai <luke.tw@...il.com>

[ Upstream commit f7c2d64bac1be2ff32f8e4f500c6e5429c1003e0 ]

If the trace for read is larger than 4096, the return
value sz will be 4096. This results in off-by-one error
on buf:

    static char buf[4096];
    ssize_t sz;

    sz = read(trace_fd, buf, sizeof(buf));
    if (sz > 0) {
        buf[sz] = 0;
        puts(buf);
    }

Signed-off-by: Chang-Hsien Tsai <luke.tw@...il.com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 samples/bpf/bpf_load.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c
index 97913e109b14..99e5a2f63e76 100644
--- a/samples/bpf/bpf_load.c
+++ b/samples/bpf/bpf_load.c
@@ -369,7 +369,7 @@ void read_trace_pipe(void)
 		static char buf[4096];
 		ssize_t sz;
 
-		sz = read(trace_fd, buf, sizeof(buf));
+		sz = read(trace_fd, buf, sizeof(buf) - 1);
 		if (sz > 0) {
 			buf[sz] = 0;
 			puts(buf);
-- 
2.20.1