[PATCH] sunrpc: Fix incorrect parsing of expiry time

[Jerry Zhang <jerry@skydio.com>]

The expiry time field is mean to be expressed in seconds since boot.
The get_expiry() function parses a relative time value in seconds.
In order to get the absolute time of seconds since boot that the given
message will expire, the right thing is to add seconds_since_boot()
to the given relative value.

Previously this logic was subtracting boot.tv_sec from the relative
value, which was causing some confusing behavior. The return type of
time64_t could possibly underflow if time since boot is greater than
the passed in relative argument. Also several checks in nfs code compare
the return value to 0 to indicate failure, and this could spuriously
be tripped if seconds since boot happened to match the argument.

Fixes: c5b29f885afe ("sunrpc: use seconds since boot in expiry cache")
Signed-off-by: Jerry Zhang <Jerry@skydio.com>
---
 include/linux/sunrpc/cache.h | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/include/linux/sunrpc/cache.h b/include/linux/sunrpc/cache.h
index ec5a555df96f..b96b1319c93d 100644
--- a/include/linux/sunrpc/cache.h
+++ b/include/linux/sunrpc/cache.h
@@ -301,16 +301,14 @@ static inline int get_time(char **bpp, time64_t *time)
 }
 
 static inline time64_t get_expiry(char **bpp)
 {
 	time64_t rv;
-	struct timespec64 boot;
 
 	if (get_time(bpp, &rv))
 		return 0;
 	if (rv < 0)
 		return 0;
-	getboottime64(&boot);
-	return rv - boot.tv_sec;
+	return rv + seconds_since_boot();
 }
 
 #endif /*  _LINUX_SUNRPC_CACHE_H_ */
-- 
2.37.3