statfs: enforce statfs[64] structure initialization

s390's struct statfs and struct statfs64 contain padding, which
field-by-field copying does not set. Initialize the respective structs
with zeros before filling them and copying them to userspace, like it's
already done for the compat versions of these structs.

Found by KMSAN.

[[email protected]: fixed typo in patch description]
Acked-by: Heiko Carstens <[email protected]>
Cc: [email protected] # v4.14+
Signed-off-by: Ilya Leoshkevich <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexander Gordeev <[email protected]>

Author: iii-i

fs/statfs.c

@@ -130,6 +130,7 @@ static int do_statfs_native(struct kstatfs *st, struct statfs __user *p)
 	if (sizeof(buf) == sizeof(*st))
 		memcpy(&buf, st, sizeof(*st));
 	else {
+		memset(&buf, 0, sizeof(buf));
 		if (sizeof buf.f_blocks == 4) {
 			if ((st->f_blocks | st->f_bfree | st->f_bavail |
 			     st->f_bsize | st->f_frsize) &
@@ -158,7 +159,6 @@ static int do_statfs_native(struct kstatfs *st, struct statfs __user *p)
 		buf.f_namelen = st->f_namelen;
 		buf.f_frsize = st->f_frsize;
 		buf.f_flags = st->f_flags;
-		memset(buf.f_spare, 0, sizeof(buf.f_spare));
 	}
 	if (copy_to_user(p, &buf, sizeof(buf)))
 		return -EFAULT;
@@ -171,6 +171,7 @@ static int do_statfs64(struct kstatfs *st, struct statfs64 __user *p)
 	if (sizeof(buf) == sizeof(*st))
 		memcpy(&buf, st, sizeof(*st));
 	else {
+		memset(&buf, 0, sizeof(buf));
 		buf.f_type = st->f_type;
 		buf.f_bsize = st->f_bsize;
 		buf.f_blocks = st->f_blocks;
@@ -182,7 +183,6 @@ static int do_statfs64(struct kstatfs *st, struct statfs64 __user *p)
 		buf.f_namelen = st->f_namelen;
 		buf.f_frsize = st->f_frsize;
 		buf.f_flags = st->f_flags;
-		memset(buf.f_spare, 0, sizeof(buf.f_spare));
 	}
 	if (copy_to_user(p, &buf, sizeof(buf)))
 		return -EFAULT;