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Subject[PATCH 4/9] fat: Add allow_utime option
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Date

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>
---

Documentation/filesystems/vfat.txt | 15 +++++++++++++++
fs/fat/file.c | 24 ++++++++++++++++++++++++
fs/fat/inode.c | 18 +++++++++++++++---
include/linux/msdos_fs.h | 1 +
4 files changed, 55 insertions(+), 3 deletions(-)

diff -puN fs/fat/file.c~fat_allow_utime fs/fat/file.c
--- linux-2.6/fs/fat/file.c~fat_allow_utime 2008-03-14 05:02:22.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/file.c 2008-03-14 05:36:19.000000000 +0900
@@ -278,11 +278,27 @@ static int fat_check_mode(const struct m
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();

@@ -300,7 +316,15 @@ int fat_setattr(struct dentry *dentry, s
}
}

+ /* 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 -puN fs/fat/inode.c~fat_allow_utime fs/fat/inode.c
--- linux-2.6/fs/fat/inode.c~fat_allow_utime 2008-03-14 05:02:22.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/inode.c 2008-03-14 05:35:37.000000000 +0900
@@ -785,6 +785,8 @@ static int fat_show_options(struct seq_f
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_f

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,
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,
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,
" 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 -puN include/linux/msdos_fs.h~fat_allow_utime include/linux/msdos_fs.h
--- linux-2.6/include/linux/msdos_fs.h~fat_allow_utime 2008-03-14 05:02:22.000000000 +0900
+++ linux-2.6-hirofumi/include/linux/msdos_fs.h 2008-03-14 05:35:37.000000000 +0900
@@ -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 */
diff -puN Documentation/filesystems/vfat.txt~fat_allow_utime Documentation/filesystems/vfat.txt
--- linux-2.6/Documentation/filesystems/vfat.txt~fat_allow_utime 2008-03-14 05:02:22.000000000 +0900
+++ linux-2.6-hirofumi/Documentation/filesystems/vfat.txt 2008-03-14 05:02:22.000000000 +0900
@@ -17,6 +17,21 @@ dmask=### -- The permission mask for
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.
_

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