[PATCH] ftrace: Replaces simple_strtoul in ftrace

[Yuran Pereira]

The function simple_strtoul performs no error checking in scenarios
where the input value overflows the intended output variable.
This results in this function successfully returning, even when the
output does not match the input string (aka the function returns
successfully even when the result is wrong).

Or as it was mentioned [1], "...simple_strtol(), simple_strtoll(),
simple_strtoul(), and simple_strtoull() functions explicitly ignore
overflows, which may lead to unexpected results in callers."
Hence, the use of those functions is discouraged.

This patch replaces all uses of the simple_strtoul with the safer
alternatives kstrtoul and kstruint.

Callers affected:
- add_rec_by_index
- set_graph_max_depth_function

Side effects of this patch:
- Since `fgraph_max_depth` is an `unsigned int`, this patch uses
  kstrtouint instead of kstrtoul to avoid any compiler warnings
  that could originate from calling the latter.
- This patch ensures that the callers of kstrtou* return accordingly
  when kstrtoul and kstruint fail for some reason.
  In this case, both callers this patch is addressing return 0 on error.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull

Signed-off-by: Yuran Pereira <yuran.pereira@xxxxxxxxxxx>
---
 kernel/trace/ftrace.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 8de8bec5f366..70217ee97322 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -4233,12 +4233,12 @@ static int
 add_rec_by_index(struct ftrace_hash *hash, struct ftrace_glob *func_g,
 		 int clear_filter)
 {
-	long index = simple_strtoul(func_g->search, NULL, 0);
+	long index;
 	struct ftrace_page *pg;
 	struct dyn_ftrace *rec;
 
 	/* The index starts at 1 */
-	if (--index < 0)
+	if (kstrtoul(func_g->search, 0, &index) || --index < 0)
 		return 0;
 
 	do_for_each_ftrace_rec(pg, rec) {
@@ -5810,9 +5810,8 @@ __setup("ftrace_graph_notrace=", set_graph_notrace_function);
 
 static int __init set_graph_max_depth_function(char *str)
 {
-	if (!str)
+	if (!str || kstrtouint(str, 0, &fgraph_max_depth))
 		return 0;
-	fgraph_max_depth = simple_strtoul(str, NULL, 0);
 	return 1;
 }
 __setup("ftrace_graph_max_depth=", set_graph_max_depth_function);
-- 
2.25.1