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Subject[PATCH 15/21] fat: Fix ATTR_RO in the case of (~umask & S_WUGO) == 0
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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>
---

fs/fat/fat.h | 33 +++++++++++++++++++++++++++++----
fs/fat/file.c | 7 ++++++-
2 files changed, 35 insertions(+), 5 deletions(-)

diff -puN fs/fat/fat.h~fat-attrs-fixes fs/fat/fat.h
--- linux-2.6/fs/fat/fat.h~fat-attrs-fixes 2008-10-13 01:49:49.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/fat.h 2008-10-13 01:49:49.000000000 +0900
@@ -117,6 +117,25 @@ static inline struct msdos_inode_info *M
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(struc
/* 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 -puN fs/fat/file.c~fat-attrs-fixes fs/fat/file.c
--- linux-2.6/fs/fat/file.c~fat-attrs-fixes 2008-10-13 01:49:49.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/file.c 2008-10-13 01:49:49.000000000 +0900
@@ -27,7 +27,12 @@ int fat_generic_ioctl(struct inode *inod
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:
_

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