linux-kernel - Re: [PATCH 6/7] cifs: Validate content of native symlink

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Message-ID: <CAH2r5mtRN04+X-J7C__qHL6S+VzFbWoRGdb=cBDQfDVLGgWwew@mail.gmail.com>
Date: Sun, 29 Sep 2024 16:48:46 -0500
From: Steve French <smfrench@...il.com>
To: Pali Rohár <pali@...nel.org>
Cc: Steve French <sfrench@...ba.org>, Paulo Alcantara <pc@...guebit.com>, 
	Ronnie Sahlberg <ronniesahlberg@...il.com>, linux-cifs@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] cifs: Validate content of native symlink

Is there any easy way to create such a symlink (with null in it)?

On Sun, Sep 29, 2024 at 1:51 PM Pali Rohár <pali@...nel.org> wrote:
>
> Check that buffer does not contain UTF-16 null codepoint
> because Linux cannot process symlink with null byte.
>
> Signed-off-by: Pali Rohár <pali@...nel.org>
> ---
>  fs/smb/client/reparse.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
> index 5a738f65b190..ca4f96c43508 100644
> --- a/fs/smb/client/reparse.c
> +++ b/fs/smb/client/reparse.c
> @@ -509,6 +509,16 @@ int smb2_parse_native_symlink(char **target, const char *buf, unsigned int len,
>         int rc;
>         int i;
>
> +       /*
> +        * Check that buffer does not contain UTF-16 null codepoint
> +        * because Linux cannot process symlink with null byte.
> +        */
> +       if (unicode && UniStrnlen((wchar_t *)buf, len/2) != len/2) {
> +               cifs_dbg(VFS, "srv returned null byte in native symlink target location\n");
> +               rc = -EIO;
> +               goto out;
> +       }
> +
>         smb_target = cifs_strndup_from_utf16(buf, len, unicode, cifs_sb->local_nls);
>         if (!smb_target) {
>                 rc = -ENOMEM;
> --
> 2.20.1
>
>


-- 
Thanks,

Steve