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Subject[patch] Refine FAT chmod checks
Hi,


when a vfat filesystem is mounted without the quiet option, chown fails,
but chmod still succeeds. I think that is wrong.

Run-tested, it does what I want it to do.

===

[fs/fat/]: Refine FAT chmod checks

Prohibit mode changes in non-quiet mode that cannot be stored reliably
with the on-disk format.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>

---
fs/fat/file.c | 47 +++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 43 insertions(+), 4 deletions(-)
Index: linux-2.6.22/fs/fat/file.c
===================================================================
--- linux-2.6.22.orig/fs/fat/file.c
+++ linux-2.6.22/fs/fat/file.c
@@ -155,6 +155,42 @@ out:
return err;
}

+static int check_mode(const struct msdos_sb_info *sbi, mode_t mode)
+{
+ mode_t req = mode & ~S_IFMT;
+
+ /*
+ * Of the r and x bits, all (subject to umask) must be present. Of the
+ * w bits, either all (subject to umask) or none must be present.
+ */
+
+ if (S_ISREG(mode)) {
+ req &= ~sbi->options.fs_fmask;
+
+ if ((req & (S_IRUGO | S_IXUGO)) !=
+ ((S_IRUGO | S_IXUGO) & ~sbi->options.fs_fmask))
+ return -EPERM;
+
+ if ((req & S_IWUGO) != 0 &&
+ (req & S_IWUGO) != (S_IWUGO & ~sbi->options.fs_fmask))
+ return -EPERM;
+ } else if (S_ISDIR(mode)) {
+ req &= ~sbi->options.fs_dmask;
+
+ if ((req & (S_IRUGO | S_IXUGO)) !=
+ ((S_IRUGO | S_IXUGO) & ~sbi->options.fs_dmask))
+ return -EPERM;
+
+ if ((req & S_IWUGO) != 0 &&
+ (req & S_IWUGO) != (S_IWUGO & ~sbi->options.fs_dmask))
+ return -EPERM;
+ } else {
+ return -EPERM;
+ }
+
+ return 0;
+}
+
int fat_notify_change(struct dentry *dentry, struct iattr *attr)
{
struct msdos_sb_info *sbi = MSDOS_SB(dentry->d_sb);
@@ -186,16 +222,19 @@ int fat_notify_change(struct dentry *den
if (((attr->ia_valid & ATTR_UID) &&
(attr->ia_uid != sbi->options.fs_uid)) ||
((attr->ia_valid & ATTR_GID) &&
- (attr->ia_gid != sbi->options.fs_gid)) ||
- ((attr->ia_valid & ATTR_MODE) &&
- (attr->ia_mode & ~MSDOS_VALID_MODE)))
+ (attr->ia_gid != sbi->options.fs_gid)))
error = -EPERM;
-
if (error) {
if (sbi->options.quiet)
error = 0;
goto out;
}
+
+ if (error == 0 && (attr->ia_valid & ATTR_MODE))
+ if ((error = check_mode(sbi, attr->ia_mode)) != 0 &&
+ sbi->options.quiet)
+ error = 0;
+
error = inode_setattr(inode, attr);
if (error)
goto out;
-
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