Re: [PATCH] smb: client: fix use-before-check of ReparseDataLength in reparse_buf_ptr()

[Paulo Alcantara <pc@manguebit.org>]

Frank Sorenson <sorenson@redhat.com> writes:

> reparse_buf_ptr() reads buf->ReparseDataLength before checking that
> count covers the full fixed header:
>
>     buf = (struct reparse_data_buffer *)((u8 *)io + off);
>     len = sizeof(*buf);                          /* 8 bytes */
>     rdlen = le16_to_cpu(buf->ReparseDataLength); /* offset 4, 2 bytes */
>
>     if (count < len || count < rdlen + len)      /* check comes after */
>
> struct reparse_data_buffer has ReparseDataLength at offset 4.  If a
> server returns OutputCount < 6, the read at offset 4-5 reaches past
> the end of the received data.  The off+count bounds against iov_len
> were already validated, but that does not protect against count being
> smaller than sizeof(*buf).
>
> Split the check: verify count >= sizeof(*buf) before reading
> ReparseDataLength, then verify count covers the data region.
>
> Fixes: a158bb66b137 ("smb: client: optimise reparse point querying")
> Cc: stable@vger.kernel.org
> Signed-off-by: Frank Sorenson <sorenson@redhat.com>

Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>