fat: Add allow_utime option

Normally utime(2) checks current process is owner of the file, or it
has CAP_FOWNER capability.  But FAT filesystem doesn't have uid/gid as
on disk info, so normal check is too unflexible.

With this option you can relax it.

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, 24 insertions, 0 deletions

diff --git a/fs/fat/file.c b/fs/fat/file.c
index e73f13a13792..d604bb132422 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -280,11 +280,27 @@ static int fat_check_mode(const struct msdos_sb_info *sbi, struct inode *inode,
         return 0;
 }
 
+static int fat_allow_set_time(struct msdos_sb_info *sbi, struct inode *inode)
+{
+        mode_t allow_utime = sbi->options.allow_utime;
+
+        if (current->fsuid != inode->i_uid) {
+                if (in_group_p(inode->i_gid))
+                        allow_utime >>= 3;
+                if (allow_utime & MAY_WRITE)
+                        return 1;
+        }
+
+        /* use a default check */
+        return 0;
+}
+
 int fat_setattr(struct dentry *dentry, struct iattr *attr)
 {
         struct msdos_sb_info *sbi = MSDOS_SB(dentry->d_sb);
         struct inode *inode = dentry->d_inode;
         int mask, error = 0;
+        unsigned int ia_valid;
 
         lock_kernel();
 
@@ -302,7 +318,15 @@ int fat_setattr(struct dentry *dentry, struct iattr *attr)
                 }
         }
 
+        /* Check for setting the inode time. */
+        ia_valid = attr->ia_valid;
+        if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET)) {
+                if (fat_allow_set_time(sbi, inode))
+                        attr->ia_valid &= ~(ATTR_MTIME_SET | ATTR_ATIME_SET);
+        }
+
         error = inode_change_ok(inode, attr);
+        attr->ia_valid = ia_valid;
         if (error) {
                 if (sbi->options.quiet)
                         error = 0;