Re: [PATCH] Input: analog - fix invalid snprintf() call
From: Rasmus Villemoes <hidden>
Date: 2021-03-23 13:30:02
Also in:
lkml
On 23/03/2021 14.14, Arnd Bergmann wrote:
From: Arnd Bergmann <arnd@arndb.de> overlapping input and output arguments to snprintf() are undefined behavior in C99:
Good luck: https://lore.kernel.org/lkml/1457469654-17059-1-git-send-email-linux@rasmusvillemoes.dk/ (local) At least 5 years ago the consensus from old-timers was that "the kernel's snprintf supports this use case, just keep it working that way".
quoted hunk ↗ jump to hunk
diff --git a/drivers/input/joystick/analog.c b/drivers/input/joystick/analog.c index f798922a4598..8c9fed3f13e2 100644 --- a/drivers/input/joystick/analog.c +++ b/drivers/input/joystick/analog.c@@ -419,14 +419,16 @@ static void analog_calibrate_timer(struct analog_port *port) static void analog_name(struct analog *analog) { - snprintf(analog->name, sizeof(analog->name), "Analog %d-axis %d-button", + int len; + + len = snprintf(analog->name, sizeof(analog->name), "Analog %d-axis %d-button", hweight8(analog->mask & ANALOG_AXES_STD), hweight8(analog->mask & ANALOG_BTNS_STD) + !!(analog->mask & ANALOG_BTNS_CHF) * 2 + hweight16(analog->mask & ANALOG_BTNS_GAMEPAD) + !!(analog->mask & ANALOG_HBTN_CHF) * 4); if (analog->mask & ANALOG_HATS_ALL) - snprintf(analog->name, sizeof(analog->name), "%s %d-hat", - analog->name, hweight16(analog->mask & ANALOG_HATS_ALL)); + len += snprintf(analog->name + len, sizeof(analog->name) - len, "%d-hat", + hweight16(analog->mask & ANALOG_HATS_ALL));
Use scnprintf, this is too fragile and hard to verify. If the first snprintf overflows, the second passes a huge size_t to snprintf which will WARN. Rasmus