Re: [PATCH RESEND 10/11] cifs: Add support for parsing WSL symlinks in version 1 format

[Pali Rohár]

On Monday 06 July 2026 20:48:18 Pali Rohár wrote:
> +	switch (version) {
> +	case 1:
> +		/*
> +		 * Layout version 1 stores the symlink target in the data section of
> +		 * the file encoded in UTF-8 without trailing null-term byte.
> +		 */
>  
> -	if (version != 2) {
> +		oparms = CIFS_OPARMS(cifs_sb, tcon, full_path, FILE_READ_DATA,
> +				     FILE_OPEN, CREATE_NOT_DIR | OPEN_REPARSE_POINT,
> +				     ACL_NO_MODE);
> +		oparms.fid = &fid;
> +		oplock = tcon->ses->server->oplocks ? REQ_OPLOCK : 0;
> +		rc = tcon->ses->server->ops->open(xid, &oparms, &oplock, NULL);
> +		if (rc)
> +			goto out;
> +
> +		free_symname_utf8 = true;
> +		symname_utf8_len = le64_to_cpu(data->fi.EndOfFile);

And Sashiko found another issue
https://sashiko.dev/#/patchset/20260706184819.22124-1-pali%40kernel.org

  Does this unconditionally read EndOfFile from the smb2_file_all_info
  struct, even when data->contains_posix_file_info is true?

  If the mount uses POSIX extensions, smb311_posix_get_fattr() populates the
  posix_fi union member instead of fi, so could this read garbage data
  overlaying DosAttributes and Inode? Also, should there be a bounds check
  against something like PATH_MAX before passing this length to kmalloc()?

I did not though about combining POSIX extensions and WSL together.

And I must admit that it is tricky that sometimes it is needed to read
data from data->posix_fi and sometimes from data->fi. Following change
should address this issue. About bounds checks, do you have any
suggestion which one to use?


diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
index 3fe57d166776..d7cb8eca7838 100644
--- a/fs/smb/client/reparse.c
+++ b/fs/smb/client/reparse.c
@@ -1114,6 +1114,7 @@ static int parse_reparse_wsl_symlink(struct reparse_wsl_symlink_data_buffer *buf
 	__le16 *symname_utf16;
 	int symname_utf16_len;
 	struct cifs_fid fid;
+	u64 file_size;
 	__u32 oplock;
 	int buf_type;
 	int rc = 0;
@@ -1133,8 +1134,12 @@ static int parse_reparse_wsl_symlink(struct reparse_wsl_symlink_data_buffer *buf
 		 * the file encoded in UTF-8 without trailing null-term byte.
 		 */

+		file_size = data->contains_posix_file_info ?
+			le64_to_cpu(data->posix_fi.EndOfFile) :
+			le64_to_cpu(data->fi.EndOfFile);
+
 		free_symname_utf8 = true;
-		symname_utf8_len = le64_to_cpu(data->fi.EndOfFile);
+		symname_utf8_len = file_size;
 		symname_utf8 = kmalloc(symname_utf8_len, GFP_KERNEL);
 		if (!symname_utf8) {
 			rc = -ENOMEM;
@@ -1162,7 +1167,7 @@ static int parse_reparse_wsl_symlink(struct reparse_wsl_symlink_data_buffer *buf
 						       &symname_utf8_len,
 						       &symname_utf8,
 						       &buf_type);
-		if (!rc && symname_utf8_len != le64_to_cpu(data->fi.EndOfFile))
+		if (!rc && symname_utf8_len != file_size)
 			rc = -EIO;

 		tcon->ses->server->ops->close(xid, tcon, &fid);