samples, bpf: fix to change the buffer size for read()

[ 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@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c
index eae7b635343d13182a4d458d3280464f6ffee4ca..6e87cc831e84287170f4ec77d8eb890e587cad6c 100644 (file)
--- 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);