Commit 3363da82 authored by Paulo Alcantara's avatar Paulo Alcantara Committed by Steve French
Browse files

smb: client: fix native SMB symlink traversal 



We've seen customers having shares mounted in paths like /??/C:/ or
/??/UNC/foo.example.com/share in order to get their native SMB
symlinks successfully followed from different mounts.

After commit 12b466eb ("cifs: Fix creating and resolving absolute NT-style symlinks"),
the client would then convert absolute paths from "/??/C:/" to "/mnt/c/"
by default.  The absolute paths would vary depending on the value of
symlinkroot= mount option.

Fix this by restoring old behavior of not trying to convert absolute
paths by default.  Only do this if symlinkroot= was _explicitly_ set.

Before patch:

  $ mount.cifs //w22-fs0/test2 /mnt/1 -o vers=3.1.1,username=xxx,password=yyy
  $ ls -l /mnt/1/symlink2
  lrwxr-xr-x 1 root root 15 Jun 20 14:22 /mnt/1/symlink2 -> /mnt/c/testfile
  $ mkdir -p /??/C:; echo foo > //??/C:/testfile
  $ cat /mnt/1/symlink2
  cat: /mnt/1/symlink2: No such file or directory

After patch:

  $ mount.cifs //w22-fs0/test2 /mnt/1 -o vers=3.1.1,username=xxx,password=yyy
  $ ls -l /mnt/1/symlink2
  lrwxr-xr-x 1 root root 15 Jun 20 14:22 /mnt/1/symlink2 -> '/??/C:/testfile'
  $ mkdir -p /??/C:; echo foo > //??/C:/testfile
  $ cat /mnt/1/symlink2
  foo

Cc: linux-cifs@vger.kernel.org
Reported-by: default avatarPierguido Lambri <plambri@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Stefan Metzmacher <metze@samba.org>
Fixes: 12b466eb ("cifs: Fix creating and resolving absolute NT-style symlinks")
Signed-off-by: default avatarPaulo Alcantara (Red Hat) <pc@manguebit.org>
Signed-off-by: default avatarSteve French <stfrench@microsoft.com>
parent 266b5d02

fs/smb/client/fs_context.c

+7 −10
Original line number Diff line number Diff line
@@ -1824,10 +1824,14 @@ static int smb3_fs_context_parse_param(struct fs_context *fc, 
			cifs_errorf(fc, "symlinkroot mount options must be absolute path\n");

			goto cifs_parse_mount_err;

		}

		kfree(ctx->symlinkroot);

		ctx->symlinkroot = kstrdup(param->string, GFP_KERNEL);

		if (!ctx->symlinkroot)

		if (strnlen(param->string, PATH_MAX) == PATH_MAX) {

			cifs_errorf(fc, "symlinkroot path too long (max path length: %u)\n",

				    PATH_MAX - 1);

			goto cifs_parse_mount_err;

		}

		kfree(ctx->symlinkroot);

		ctx->symlinkroot = param->string;

		param->string = NULL;

		break;

	}

	/* case Opt_ignore: - is ignored as expected ... */
@@ -1837,13 +1841,6 @@ static int smb3_fs_context_parse_param(struct fs_context *fc, 
		goto cifs_parse_mount_err;

	}



	/*

	 * By default resolve all native absolute symlinks relative to "/mnt/".

	 * Same default has drvfs driver running in WSL for resolving SMB shares.

	 */

	if (!ctx->symlinkroot)

		ctx->symlinkroot = kstrdup("/mnt/", GFP_KERNEL);



	return 0;



 cifs_parse_mount_err:

fs/smb/client/reparse.c

+13 −9
Original line number Diff line number Diff line
@@ -57,6 +57,7 @@ static int create_native_symlink(const unsigned int xid, struct inode *inode, 
	struct reparse_symlink_data_buffer *buf = NULL;

	struct cifs_open_info_data data = {};

	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);

	const char *symroot = cifs_sb->ctx->symlinkroot;

	struct inode *new;

	struct kvec iov;

	__le16 *path = NULL;
@@ -82,7 +83,8 @@ static int create_native_symlink(const unsigned int xid, struct inode *inode, 
		.symlink_target = symlink_target,

	};



	if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS) && symname[0] == '/') {

	if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS) &&

	    symroot && symname[0] == '/') {

		/*

		 * This is a request to create an absolute symlink on the server

		 * which does not support POSIX paths, and expects symlink in
@@ -92,7 +94,7 @@ static int create_native_symlink(const unsigned int xid, struct inode *inode, 
		 * ensure compatibility of this symlink stored in absolute form

		 * on the SMB server.

		 */

		if (!strstarts(symname, cifs_sb->ctx->symlinkroot)) {

		if (!strstarts(symname, symroot)) {

			/*

			 * If the absolute Linux symlink target path is not

			 * inside "symlinkroot" location then there is no way
@@ -101,12 +103,12 @@ static int create_native_symlink(const unsigned int xid, struct inode *inode, 
			cifs_dbg(VFS,

				 "absolute symlink '%s' cannot be converted to NT format "

				 "because it is outside of symlinkroot='%s'\n",

				 symname, cifs_sb->ctx->symlinkroot);

				 symname, symroot);

			rc = -EINVAL;

			goto out;

		}

		len = strlen(cifs_sb->ctx->symlinkroot);

		if (cifs_sb->ctx->symlinkroot[len-1] != '/')

		len = strlen(symroot);

		if (symroot[len - 1] != '/')

			len++;

		if (symname[len] >= 'a' && symname[len] <= 'z' &&

		    (symname[len+1] == '/' || symname[len+1] == '\0')) {
@@ -782,6 +784,7 @@ int smb2_parse_native_symlink(char **target, const char *buf, unsigned int len, 
			      const char *full_path,

			      struct cifs_sb_info *cifs_sb)

{

	const char *symroot = cifs_sb->ctx->symlinkroot;

	char sep = CIFS_DIR_SEP(cifs_sb);

	char *linux_target = NULL;

	char *smb_target = NULL;
@@ -815,7 +818,8 @@ int smb2_parse_native_symlink(char **target, const char *buf, unsigned int len, 
		goto out;

	}



	if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS) && !relative) {

	if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS) &&

	    symroot && !relative) {

		/*

		 * This is an absolute symlink from the server which does not

		 * support POSIX paths, so the symlink is in NT-style path.
@@ -907,15 +911,15 @@ int smb2_parse_native_symlink(char **target, const char *buf, unsigned int len, 
		}



		abs_path_len = strlen(abs_path)+1;

		symlinkroot_len = strlen(cifs_sb->ctx->symlinkroot);

		if (cifs_sb->ctx->symlinkroot[symlinkroot_len-1] == '/')

		symlinkroot_len = strlen(symroot);

		if (symroot[symlinkroot_len - 1] == '/')

			symlinkroot_len--;

		linux_target = kmalloc(symlinkroot_len + 1 + abs_path_len, GFP_KERNEL);

		if (!linux_target) {

			rc = -ENOMEM;

			goto out;

		}

		memcpy(linux_target, cifs_sb->ctx->symlinkroot, symlinkroot_len);

		memcpy(linux_target, symroot, symlinkroot_len);

		linux_target[symlinkroot_len] = '/';

		memcpy(linux_target + symlinkroot_len + 1, abs_path, abs_path_len);

	} else if (smb_target[0] == sep && relative) {