[PATCH 1/3] tracing: detect the string termination character when parsing user input string

changbin.du
2018-01-09T10:05:39Z

From: Changbin Du <changbin.du@intel.com>

The usersapce can give a '\0' terminated C string or even has '\0' at the
middle of input buffer. We need handle both these two cases correctly.

Before this change, trace_get_user() will return a parsed string "\0" in
below case. It is not expected (expects it skip all inputs) and cause the
caller failed.

open("/sys/kernel/debug/tracing//set_ftrace_pid", O_WRONLY|O_TRUNC) = 3
write(3, " \0", 2) = -1 EINVAL (Invalid argument)

This patch try to make the parser '\0' aware to fix such issue.

Since the caller expects trace_get_user() to parse whole input buffer, so
this patch treat '\0' as a separator as whitespace.

Signed-off-by: Changbin Du <changbin.du@intel.com>
---
kernel/trace/trace.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2a8d8a2..18526a1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1194,9 +1194,14 @@ void trace_parser_put(struct trace_parser *parser)
parser->buffer = NULL;
}

+static inline bool is_space_or_zero(char ch)
+{
+ return isspace(ch) || !ch;
+}
+
/*
- * trace_get_user - reads the user input string separated by space
- * (matched by isspace(ch))
+ * trace_get_user - reads the user input string separated by space or '\0'
+ * (matched by is_space_or_zero(ch))
*
* For each string found the 'struct trace_parser' is updated,
* and the function returns.
@@ -1228,7 +1233,7 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
*/
if (!parser->cont) {
/* skip white space */
- while (cnt && isspace(ch)) {
+ while (cnt && is_space_or_zero(ch)) {
ret = get_user(ch, ubuf++);
if (ret)
goto out;
@@ -1237,7 +1242,7 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
}

/* only spaces were written */
- if (isspace(ch)) {
+ if (is_space_or_zero(ch)) {
*ppos += read;
ret = read;
goto out;
@@ -1247,7 +1252,7 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
}

/* read the non-space input */
- while (cnt && !isspace(ch)) {
+ while (cnt && !is_space_or_zero(ch)) {
if (parser->idx < parser->size - 1)
parser->buffer[parser->idx++] = ch;
else {
@@ -1262,7 +1267,7 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
}

/* We either got finished input or we have to wait for another call. */
- if (isspace(ch)) {
+ if (is_space_or_zero(ch)) {
parser->buffer[parser->idx] = 0;
parser->cont = false;
} else if (parser->idx < parser->size - 1) {
--
2.7.4