[PATCH 4/6] misc: fix gcc-7 sprintf warnings -Wformat-overflow

[Ruediger Meier <sweet_f_a@gmx.de>]

From: Ruediger Meier <ruediger.meier@ga-group.nl>

../login-utils/last.c: In function ‘main’:
../login-utils/last.c:624:23: warning: ‘%s’ directive writing up to 31 bytes into a region of size 27 [-Wformat-overflow=]
   sprintf(path, "/dev/%s", ut->ut_line);
                       ^~   ~~
../login-utils/last.c:624:3: note: ‘sprintf’ output between 6 and 37 bytes into a destination of size 32
   sprintf(path, "/dev/%s", ut->ut_line);

../libblkid/src/devname.c: In function 'probe_one':
../libblkid/src/devname.c:166:29: warning: '%s' directive writing up to 255 bytes into a region of size 245 [-Wformat-overflow=]
   sprintf(path, "/sys/block/%s/slaves", de->d_name);
                             ^~
../libblkid/src/devname.c:166:3: note: 'sprintf' output between 19 and 274 bytes into a destination of size 256
   sprintf(path, "/sys/block/%s/slaves", de->d_name);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
---
 libblkid/src/devname.c | 2 +-
 login-utils/last.c     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libblkid/src/devname.c b/libblkid/src/devname.c
index ba3c57a41..59029ec06 100644
--- a/libblkid/src/devname.c
+++ b/libblkid/src/devname.c
@@ -152,7 +152,7 @@ static int is_dm_leaf(const char *devname)
 {
 	struct dirent	*de, *d_de;
 	DIR		*dir, *d_dir;
-	char		path[256];
+	char		path[NAME_MAX + 18 + 1];
 	int		ret = 1;
 
 	if ((dir = opendir("/sys/block")) == NULL)
diff --git a/login-utils/last.c b/login-utils/last.c
index f93ec7fbf..c90b574e5 100644
--- a/login-utils/last.c
+++ b/login-utils/last.c
@@ -598,7 +598,7 @@ static void __attribute__((__noreturn__)) usage(const struct last_control *ctl,
 static int is_phantom(const struct last_control *ctl, struct utmpx *ut)
 {
 	struct passwd *pw;
-	char path[32];
+	char path[sizeof(ut->ut_line) + 16];
 	int ret = 0;
 
 	if (ut->ut_tv.tv_sec < ctl->boot_time.tv_sec)
-- 
2.12.3