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>

diff --git a/Documentation/filesystems/vfat.txt b/Documentation/filesystems/vfat.txt
index fcc123f..2d5e1e5 100644 (file)
--- a/Documentation/filesystems/vfat.txt
+++ b/Documentation/filesystems/vfat.txt
@@ -17,6 +17,21 @@ dmask=###     -- The permission mask for the directory.
 fmask=###     -- The permission mask for files.
                  The default is the umask of current process.
 
+allow_utime=### -- This option controls the permission check of mtime/atime.
+
+                  20 - If current process is in group of file's group ID,
+                       you can change timestamp.
+                   2 - Other users can change timestamp.
+
+                 The default is set from `dmask' option. (If the directory is
+                 writable, utime(2) is also allowed. I.e. ~dmask & 022)
+
+                 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 on disk, so normal
+                 check is too unflexible. With this option you can
+                 relax it.
+
 codepage=###  -- Sets the codepage number for converting to shortname
                 characters on FAT filesystem.
                 By default, FAT_DEFAULT_CODEPAGE setting is used.

diff --git a/fs/fat/file.c b/fs/fat/file.c
index e73f13a..d604bb1 100644 (file)
--- 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;

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index f22f287..886f609 100644 (file)
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -785,6 +785,8 @@ static int fat_show_options(struct seq_file *m, struct vfsmount *mnt)
                seq_printf(m, ",gid=%u", opts->fs_gid);
        seq_printf(m, ",fmask=%04o", opts->fs_fmask);
        seq_printf(m, ",dmask=%04o", opts->fs_dmask);
+       if (opts->allow_utime)
+               seq_printf(m, ",allow_utime=%04o", opts->allow_utime);
        if (sbi->nls_disk)
                seq_printf(m, ",codepage=%s", sbi->nls_disk->charset);
        if (isvfat) {
@@ -840,9 +842,9 @@ static int fat_show_options(struct seq_file *m, struct vfsmount *mnt)
 
 enum {
        Opt_check_n, Opt_check_r, Opt_check_s, Opt_uid, Opt_gid,
-       Opt_umask, Opt_dmask, Opt_fmask, Opt_codepage, Opt_usefree, Opt_nocase,
-       Opt_quiet, Opt_showexec, Opt_debug, Opt_immutable,
-       Opt_dots, Opt_nodots,
+       Opt_umask, Opt_dmask, Opt_fmask, Opt_allow_utime, Opt_codepage,
+       Opt_usefree, Opt_nocase, Opt_quiet, Opt_showexec, Opt_debug,
+       Opt_immutable, Opt_dots, Opt_nodots,
        Opt_charset, Opt_shortname_lower, Opt_shortname_win95,
        Opt_shortname_winnt, Opt_shortname_mixed, Opt_utf8_no, Opt_utf8_yes,
        Opt_uni_xl_no, Opt_uni_xl_yes, Opt_nonumtail_no, Opt_nonumtail_yes,
@@ -861,6 +863,7 @@ static match_table_t fat_tokens = {
        {Opt_umask, "umask=%o"},
        {Opt_dmask, "dmask=%o"},
        {Opt_fmask, "fmask=%o"},
+       {Opt_allow_utime, "allow_utime=%o"},
        {Opt_codepage, "codepage=%u"},
        {Opt_usefree, "usefree"},
        {Opt_nocase, "nocase"},
@@ -932,6 +935,7 @@ static int parse_options(char *options, int is_vfat, int silent, int *debug,
        opts->fs_uid = current->uid;
        opts->fs_gid = current->gid;
        opts->fs_fmask = opts->fs_dmask = current->fs->umask;
+       opts->allow_utime = -1;
        opts->codepage = fat_default_codepage;
        opts->iocharset = fat_default_iocharset;
        if (is_vfat)
@@ -1019,6 +1023,11 @@ static int parse_options(char *options, int is_vfat, int silent, int *debug,
                                return 0;
                        opts->fs_fmask = option;
                        break;
+               case Opt_allow_utime:
+                       if (match_octal(&args[0], &option))
+                               return 0;
+                       opts->allow_utime = option & (S_IWGRP | S_IWOTH);
+                       break;
                case Opt_codepage:
                        if (match_int(&args[0], &option))
                                return 0;
@@ -1101,6 +1110,9 @@ static int parse_options(char *options, int is_vfat, int silent, int *debug,
                       " for FAT filesystems, filesystem will be case sensitive!\n");
        }
 
+       /* If user doesn't specify allow_utime, it's initialized from dmask. */
+       if (opts->allow_utime == (unsigned short)-1)
+               opts->allow_utime = ~opts->fs_dmask & (S_IWGRP | S_IWOTH);
        if (opts->unicode_xlate)
                opts->utf8 = 0;
 

diff --git a/include/linux/msdos_fs.h b/include/linux/msdos_fs.h
index c4bed98..81fb9bc 100644 (file)
--- a/include/linux/msdos_fs.h
+++ b/include/linux/msdos_fs.h
@@ -195,6 +195,7 @@ struct fat_mount_options {
        char *iocharset;          /* Charset used for filename input/display */
        unsigned short shortname; /* flags for shortname display/create rule */
        unsigned char name_check; /* r = relaxed, n = normal, s = strict */
+       unsigned short allow_utime;/* permission for setting the [am]time */
        unsigned quiet:1,         /* set = fake successful chmods and chowns */
                 showexec:1,      /* set = only set x bit for com/exe/bat */
                 sys_immutable:1, /* set = system files are immutable */