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Commit 11a7b371 authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Al Viro
Browse files

fs: allow AT_EMPTY_PATH in linkat(), limit that to CAP_DAC_READ_SEARCH 



We don't want to allow creation of private hardlinks by different application
using the fd passed to them via SCM_RIGHTS. So limit the null relative name
usage in linkat syscall to CAP_DAC_READ_SEARCH

Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
parent 326be7b4

fs/namei.c

+16 −4
Original line number Diff line number Diff line
@@ -2945,15 +2945,27 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname, 
	struct dentry *new_dentry;

	struct nameidata nd;

	struct path old_path;

	int how = 0;

	int error;

	char *to;



	if ((flags & ~AT_SYMLINK_FOLLOW) != 0)

	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)

		return -EINVAL;

	/*

	 * To use null names we require CAP_DAC_READ_SEARCH

	 * This ensures that not everyone will be able to create

	 * handlink using the passed filedescriptor.

	 */

	if (flags & AT_EMPTY_PATH) {

		if (!capable(CAP_DAC_READ_SEARCH))

			return -ENOENT;

		how = LOOKUP_EMPTY;

	}



	if (flags & AT_SYMLINK_FOLLOW)

		how |= LOOKUP_FOLLOW;



	error = user_path_at(olddfd, oldname,

			     flags & AT_SYMLINK_FOLLOW ? LOOKUP_FOLLOW : 0,

			     &old_path);

	error = user_path_at(olddfd, oldname, how, &old_path);

	if (error)

		return error;