fs/fat/: refine chmod checks (19c561a6) · Commits · 戴 / test

Prohibit mode changes in non-quiet mode that cannot be stored reliably with the on-disk format. Suppose a vfat filesystem is mounted with umask=0 and [not-quiet]. Then all files will have mode 0777. Trying to change the owner will fail, because fat does not know about owners or groups. chmod 0770, on the other hand, will succeed, even though fat does not know about the permission triplet [user/group/other]. So this patch changes fat's not-quiet behavior so that only UNIX modes are accepted that can be mapped lossless between the fat disk format and the local system. There is only one attribute, and that is the readonly attribute, which is mapped to the UNIX write permission bit(s). chmod 0555 is therefore valid (taking away the +w bits <=> setting the readonly attribute). Since chmod 0775 and chmod 0755 is an ambiguous case as to whether to set or clear the readonly bit, these modes are also denied. In quiet mode, chmod and chown will continue to "succeed" as they did before, meaning that a subsequent stat() will temporarily return the new mode as long as the inode is not reread from disk, and chown will silently do nothing, not even return the new uid/gid in stat(). Signed-off-by:

Jan Engelhardt <jengelh@computergmbh.de> Cc: 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>

fs/fat/file.c

+44 −3

Original line number	Diff line number	Diff line
		@@ -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);
		@@ -186,9 +222,7 @@ int fat_notify_change(struct dentry dentry, struct iattr attr)
		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) {
		@@ -196,6 +230,13 @@ int fat_notify_change(struct dentry dentry, struct iattr attr)
		error = 0;
		goto out;
		}

		if (attr->ia_valid & ATTR_MODE) {
		error = check_mode(sbi, attr->ia_mode);
		if (error != 0 && !sbi->options.quiet)
		goto out;
		}

		error = inode_setattr(inode, attr);
		if (error)
		goto out;

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