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Subject[PATCH] kstrtox: make kstrtobool_from_user() very strict
Once upon a time module parameter parsing code accepted
0, 1, y, n, Y and N for boolean values. Gratituous but contained
to module code and thus tolerable.

Commit ef951599074ba4fad2d0efa0a977129b41e6d203
("lib: move strtobool() to kstrtobool()") promoted that ugly wart
to kstrtobool() and, more importantly, kstrtobool_from_user().

Later set of accepted values was expanded to "on" and "of".
Now there are 6+8=14(!) valid strings for a boolean.

This patch reduces set of accepted values to "0" and "1"
(with optional newline) in spirit with other kstrto*() functions.

I'm starting with kstrtobool_from_user() as it is explicitly designed
to be used for interacting with userspace. Currently there are 9 users
all debug code, so there is hope.

Please send before 4.16 so no real users start to depend on verbose behaviour.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

lib/kstrtox.c | 32 +++++++++++++++++++++++++++-----
1 file changed, 27 insertions(+), 5 deletions(-)

--- a/lib/kstrtox.c
+++ b/lib/kstrtox.c
@@ -368,19 +368,41 @@ int kstrtobool(const char *s, bool *res)
EXPORT_SYMBOL(kstrtobool);

/*
- * Since "base" would be a nonsense argument, this open-codes the
- * _from_user helper instead of using the helper macro below.
+ * Convert string to boolean:
+ * 0 => false
+ * 1 => true
+ * 0\n => false
+ * 1\n => true
+ *
+ * Return 0 on success or -E otherwise.
*/
int kstrtobool_from_user(const char __user *s, size_t count, bool *res)
{
- /* Longest string needed to differentiate, newline, terminator */
- char buf[4];
+ /* 0|1, newline, terminator */
+ char buf[3], *p;
+ bool val;

count = min(count, sizeof(buf) - 1);
if (copy_from_user(buf, s, count))
return -EFAULT;
buf[count] = '\0';
- return kstrtobool(buf, res);
+
+ p = buf;
+ if (*p == '0')
+ val = false;
+ else if (*p == '1')
+ val = true;
+ else
+ return -EINVAL;
+ p++;
+
+ if (*p == '\n')
+ p++;
+ if (*p)
+ return -EINVAL;
+
+ *res = val;
+ return 0;
}
EXPORT_SYMBOL(kstrtobool_from_user);

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