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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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