vfs: add NOFOLLOW flag to umount(2) (db1f05bb) · Commits · 戴 / test

Add a new UMOUNT_NOFOLLOW flag to umount(2). This is needed to prevent symlink attacks in unprivileged unmounts (fuse, samba, ncpfs). Additionally, return -EINVAL if an unknown flag is used (and specify an explicitly unused flag: UMOUNT_UNUSED). This makes it possible for the caller to determine if a flag is supported or not. CC: Eugene Teo <eugene@redhat.com> CC: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by:

Miklos Szeredi <mszeredi@suse.cz> Signed-off-by:

Al Viro <viro@zeniv.linux.org.uk>

fs/namespace.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -1136,8 +1136,15 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
		{
		struct path path;
		int retval;
		int lookup_flags = 0;

		retval = user_path(name, &path);
		if (flags & ~(MNT_FORCE \| MNT_DETACH \| MNT_EXPIRE \| UMOUNT_NOFOLLOW))
		return -EINVAL;

		if (!(flags & UMOUNT_NOFOLLOW))
		lookup_flags \|= LOOKUP_FOLLOW;

		retval = user_path_at(AT_FDCWD, name, lookup_flags, &path);
		if (retval)
		goto out;
		retval = -EINVAL;

include/linux/fs.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -1305,6 +1305,8 @@ extern int send_sigurg(struct fown_struct *fown);
		#define MNT_FORCE 0x00000001 /* Attempt to forcibily umount */
		#define MNT_DETACH 0x00000002 /* Just detach from the tree */
		#define MNT_EXPIRE 0x00000004 /* Mark for expiry */
		#define UMOUNT_NOFOLLOW 0x00000008 /* Don't follow symlink on umount */
		#define UMOUNT_UNUSED 0x80000000 /* Flag guaranteed to be unused */

		extern struct list_head super_blocks;
		extern spinlock_t sb_lock;

Admin message