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Subject[PATCH] rtc-efi: 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?

Reported-by: Raymund Will <rw@suse.de>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
drivers/rtc/rtc-efi.c | 32 +++++++++++++++++++++++++++-----
1 file changed, 27 insertions(+), 5 deletions(-)

--- 3.15-rc8/drivers/rtc/rtc-efi.c
+++ 3.15-rc8-EFI-RTC-check-time/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 *wti
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, s
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
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 *
return -EINVAL;
}

- convert_from_efi_time(&eft, tm);
+ if (!convert_from_efi_time(&eft, tm))
+ return -EIO;

return rtc_valid_tm(tm);
}




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