[PATCH] lib/vdso: Make clock_getres() POSIX compliant again

[Thomas Gleixner]

A recent commit removed the NULL pointer check from the clock_getres()
implementation causing a test case to fault.

POSIX requires an explicit NULL pointer check for clock_getres() aside of
the validity check of the clock_id argument for obscure reasons.

Add it back for both 32bit and 64bit.

Note, this is only a partial revert of the offending commit which does not
bring back the broken fallback invocation in the the 32bit compat
implementations of clock_getres() and clock_gettime().

Fixes: a9446a906f52 ("lib/vdso/32: Remove inconsistent NULL pointer checks")
Reported-by: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 lib/vdso/gettimeofday.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -214,9 +214,10 @@ int __cvdso_clock_getres_common(clockid_
 		return -1;
 	}
 
-	res->tv_sec = 0;
-	res->tv_nsec = ns;
-
+	if (likely(res)) {
+		res->tv_sec = 0;
+		res->tv_nsec = ns;
+	}
 	return 0;
 }
 
@@ -245,7 +246,7 @@ static __maybe_unused int
 		ret = clock_getres_fallback(clock, &ts);
 #endif
 
-	if (likely(!ret)) {
+	if (likely(!ret && res)) {
 		res->tv_sec = ts.tv_sec;
 		res->tv_nsec = ts.tv_nsec;
 	}