drivers/rtc/rtc-efi.c: check for invalid data coming back from UEFI

In particular seeing zero in eft->month is problematic, as it results in
-1 (converted to unsigned int, i.e.  yielding 0xffffffff) getting passed
to rtc_year_days(), where the value gets used as an array index
(normally resulting in a crash).  This was observed with the driver
enabled on x86 on some Fujitsu system (with possibly not up to date
firmware, but anyway).

Perhaps efi_read_alarm() should not fail if neither enabled nor pending
are set, but the returned time is invalid?

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reported-by: Raymund Will <rw@suse.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Jingoo Han <jg1.han@samsung.com>
Acked-by: Lee, Chun-Yi <jlee@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 27 insertions, 5 deletions

diff --git a/drivers/rtc/rtc-efi.c b/drivers/rtc/rtc-efi.c
index c4c38431012e..8225b89de810 100644
--- a/drivers/rtc/rtc-efi.c
+++ b/drivers/rtc/rtc-efi.c
@@ -17,6 +17,7 @@
 
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/stringify.h>
 #include <linux/time.h>
 #include <linux/platform_device.h>
 #include <linux/rtc.h>
@@ -48,8 +49,8 @@ compute_wday(efi_time_t *eft)
         int y;
         int ndays = 0;
 
-        if (eft->year < 1998) {
-                pr_err("EFI year < 1998, invalid date\n");
+        if (eft->year < EFI_RTC_EPOCH) {
+                pr_err("EFI year < " __stringify(EFI_RTC_EPOCH) ", invalid date\n");
                 return -1;
         }
 
@@ -78,19 +79,36 @@ convert_to_efi_time(struct rtc_time *wtime, efi_time_t *eft)
         eft->timezone   = EFI_UNSPECIFIED_TIMEZONE;
 }
 
-static void
+static bool
 convert_from_efi_time(efi_time_t *eft, struct rtc_time *wtime)
 {
         memset(wtime, 0, sizeof(*wtime));
+
+        if (eft->second >= 60)
+                return false;
         wtime->tm_sec  = eft->second;
+
+        if (eft->minute >= 60)
+                return false;
         wtime->tm_min  = eft->minute;
+
+        if (eft->hour >= 24)
+                return false;
         wtime->tm_hour = eft->hour;
+
+        if (!eft->day || eft->day > 31)
+                return false;
         wtime->tm_mday = eft->day;
+
+        if (!eft->month || eft->month > 12)
+                return false;
         wtime->tm_mon  = eft->month - 1;
         wtime->tm_year = eft->year - 1900;
 
         /* day of the week [0-6], Sunday=0 */
         wtime->tm_wday = compute_wday(eft);
+        if (wtime->tm_wday < 0)
+                return false;
 
         /* day in the year [1-365]*/
         wtime->tm_yday = compute_yday(eft);
@@ -106,6 +124,8 @@ convert_from_efi_time(efi_time_t *eft, struct rtc_time *wtime)
         default:
                 wtime->tm_isdst = -1;
         }
+
+        return true;
 }
 
 static int efi_read_alarm(struct device *dev, struct rtc_wkalrm *wkalrm)
@@ -122,7 +142,8 @@ static int efi_read_alarm(struct device *dev, struct rtc_wkalrm *wkalrm)
         if (status != EFI_SUCCESS)
                 return -EINVAL;
 
-        convert_from_efi_time(&eft, &wkalrm->time);
+        if (!convert_from_efi_time(&eft, &wkalrm->time))
+                return -EIO;
 
         return rtc_valid_tm(&wkalrm->time);
 }
@@ -163,7 +184,8 @@ static int efi_read_time(struct device *dev, struct rtc_time *tm)
                 return -EINVAL;
         }
 
-        convert_from_efi_time(&eft, tm);
+        if (!convert_from_efi_time(&eft, tm))
+                return -EIO;
 
         return rtc_valid_tm(tm);
 }