netdev - [PATCH] samples: bpf: fix: change the buffer size for read()

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Message-Id: <20190519090544.26971-1-luke.tw@gmail.com>
Date:   Sun, 19 May 2019 09:05:44 +0000
From:   Chang-Hsien Tsai <luke.tw@...il.com>
To:     netdev@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net, kafai@...com,
        songliubraving@...com, yhs@...com, luke.tw@...il.com
Subject: [PATCH] samples: bpf: fix: change the buffer size for read()

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>
---
 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 eae7b635343d..d4da90070b58 100644
--- a/samples/bpf/bpf_load.c
+++ b/samples/bpf/bpf_load.c
@@ -678,7 +678,7 @@ 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);
-- 
2.17.1