linux-kernel - [PATCH V2 1/2] tracing/probes: Fix a warning message to show correct maximum length

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Date:   Fri, 10 Feb 2017 22:21:55 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH V2 1/2] tracing/probes: Fix a warning message to show correct maximum length

Since tracing/*probe_events will accept a probe definition
up to 4096 - 2 ('\n' and '\0') bytes, it must show 4094 instead
of 4096 in warning message.

Note that there is one possible case of exceed 4094. If user
prepare 4096 bytes null-terminated string and syscall write
it with the count == 4095, then it can be accepted. However,
if user puts a '\n' after that, it must rejected.
So IMHO, the warning message should indicate shorter one,
since it is safer.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 kernel/trace/trace_probe.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 2a06f1f..847c1e0 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -678,8 +678,9 @@ ssize_t traceprobe_probes_write(struct file *file, const char __user *buffer,
 				if (done + size < count) {
 					if (buf != kbuf)
 						break;
+					/* This can accept WRITE_BUFSIZE - 2 ('\n' + '\0') */
 					pr_warn("Line length is too long: Should be less than %d\n",
-						WRITE_BUFSIZE);
+						WRITE_BUFSIZE - 2);
 					ret = -EINVAL;
 					goto out;
 				}