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>

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 3b4753a..313b645 100644 (file)
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -117,6 +117,25 @@ static inline struct msdos_inode_info *MSDOS_I(struct inode *inode)
        return container_of(inode, struct msdos_inode_info, vfs_inode);
 }
 
+/*
+ * If ->i_mode can't hold S_IWUGO (i.e. ATTR_RO), we use ->i_attrs to
+ * save ATTR_RO instead of ->i_mode.
+ */
+static inline int fat_mode_can_hold_ro(struct inode *inode)
+{
+       struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
+       mode_t mask;
+
+       if (S_ISDIR(inode->i_mode))
+               mask = ~sbi->options.fs_dmask;
+       else
+               mask = ~sbi->options.fs_fmask;
+
+       if (!(mask & S_IWUGO))
+               return 0;
+       return 1;
+}
+
 /* Convert attribute bits and a mask to the UNIX mode. */
 static inline mode_t fat_make_mode(struct msdos_sb_info *sbi,
                                   u8 attrs, mode_t mode)
@@ -133,14 +152,20 @@ static inline mode_t fat_make_mode(struct msdos_sb_info *sbi,
 /* Return the FAT attribute byte for this inode */
 static inline u8 fat_make_attrs(struct inode *inode)
 {
-       return ((inode->i_mode & S_IWUGO) ? ATTR_NONE : ATTR_RO) |
-               (S_ISDIR(inode->i_mode) ? ATTR_DIR : ATTR_NONE) |
-               MSDOS_I(inode)->i_attrs;
+       u8 attrs = MSDOS_I(inode)->i_attrs;
+       if (S_ISDIR(inode->i_mode))
+               attrs |= ATTR_DIR;
+       if (fat_mode_can_hold_ro(inode) && !(inode->i_mode & S_IWUGO))
+               attrs |= ATTR_RO;
+       return attrs;
 }
 
 static inline void fat_save_attrs(struct inode *inode, u8 attrs)
 {
-       MSDOS_I(inode)->i_attrs = attrs & ATTR_UNUSED;
+       if (fat_mode_can_hold_ro(inode))
+               MSDOS_I(inode)->i_attrs = attrs & ATTR_UNUSED;
+       else
+               MSDOS_I(inode)->i_attrs = attrs & (ATTR_UNUSED | ATTR_RO);
 }
 
 static inline unsigned char fat_checksum(const __u8 *name)

diff --git a/fs/fat/file.c b/fs/fat/file.c
index f5a7e90..81b15c6 100644 (file)
--- 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: