fat: Fix ATTR_RO in the case of (~umask & S_WUGO) == 0

If inode->i_mode doesn't have S_WUGO, current code assumes it means
ATTR_RO.  However, if (~[ufd]mask & S_WUGO) == 0, inode->i_mode can't
hold S_WUGO. Therefore the updated directory entry will always have
ATTR_RO.

This adds fat_mode_can_hold_ro() to check it. And if inode->i_mode
can't hold, uses -i_attrs to hold ATTR_RO instead.

With this, we don't set ATTR_RO unless users change it via ioctl() if
(~[ufd]mask & S_WUGO) == 0.

And on FAT_IOCTL_GET_ATTRIBUTES path, this adds ->i_mutex to it for
not returning the partially updated attributes by FAT_IOCTL_SET_ATTRIBUTES
to userland.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/fat/file.c b/fs/fat/file.c
index f5a7e907a8fa..81b15c623803 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -27,7 +27,12 @@ int fat_generic_ioctl(struct inode *inode, struct file *filp,
         switch (cmd) {
         case FAT_IOCTL_GET_ATTRIBUTES:
         {
-                u32 attr = fat_make_attrs(inode);
+                u32 attr;
+
+                mutex_lock(&inode->i_mutex);
+                attr = fat_make_attrs(inode);
+                mutex_unlock(&inode->i_mutex);
+
                 return put_user(attr, user_attr);
         }
         case FAT_IOCTL_SET_ATTRIBUTES: