[PATCH] fat: fat2rtc: Sanitize timestamps

[Heinrich Schuchardt]

Am 12. Juli 2024 10:24:54 MESZ schrieb Richard Weinberger <richard at nod.at>:
>Make sure that tm_mday and tm_mon are within the expected
>range. Upper layers such as rtc_calc_weekday() will use
>them as lookup keys for arrays and this can cause out of
>bounds memory accesses.

rtc_calc_weekday() might receive invalid input from other sources. Shouldn't the function always validate its input before array access?

Having a library function for validating a struct rtc_time would be preferable to repeating ourselves in code.

Best regards

Heinrich

>
>Signed-off-by: Richard Weinberger <richard at nod.at>
>---
> fs/fat/fat.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
>diff --git a/fs/fat/fat.c b/fs/fat/fat.c
>index 2dd9d4e72d..f9096e8932 100644
>--- a/fs/fat/fat.c
>+++ b/fs/fat/fat.c
>@@ -1253,8 +1253,9 @@ out:
>  */
> static void __maybe_unused fat2rtc(u16 date, u16 time, struct rtc_time *tm)
> {
>-	tm->tm_mday = date & 0x1f;
>-	tm->tm_mon = (date & 0x1e0) >> 5;
>+	tm->tm_mday = max(1, date & 0x1f);
>+	tm->tm_mon = clamp((date & 0x1e0) >> 5, 1, 12);
>+
> 	tm->tm_year = (date >> 9) + 1980;
> 
> 	tm->tm_sec = (time & 0x1f) << 1;