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Commit db1f05bb authored by Miklos Szeredi's avatar Miklos Szeredi Committed by Al Viro
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vfs: add NOFOLLOW flag to umount(2) 



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: default avatarMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 440b3c6c

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;