[PATCH AUTOSEL 4.19 04/60] samples, bpf: fix to change the buffer size for read()

Sasha Levin
2019-06-27T00:36:35Z

From: Chang-Hsien Tsai <luke.tw@gmail.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@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.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 cf40a8284a38..5061a2ec4564 100644
--- a/samples/bpf/bpf_load.c
+++ b/samples/bpf/bpf_load.c
@@ -677,7 +677,7 @@ 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