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 12b466eb52d9 ("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: Pierguido Lambri <plambri@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Stefan Metzmacher <metze@samba.org>
Fixes: 12b466eb52d9 ("cifs: Fix creating and resolving absolute NT-style symlinks")
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
index a634a34d4086a049fe72e9093a092eaf6028c031..59ccc2229ab3008a0a0e580e3737f81c53b2720d 100644 (file)
--- a/fs/smb/client/fs_context.c
+++ b/fs/smb/client/fs_context.c
@@ -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:

diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
index 1c40e42e4d8973693072a206b168866a0b09f852..5fa29a97ac154b6b4a0c4709f1ad96c565c089f9 100644 (file)
--- a/fs/smb/client/reparse.c
+++ b/fs/smb/client/reparse.c
@@ -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 @@ globalroot:
                }
 
                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) {