[PATCH v3] smb: client: reject a tree connect response whose byte count is too small

[Paulo Alcantara]

Bryam Vargas via B4 Relay <devnull+hexlabsecurity.proton.me at kernel.org>
writes:

> From: Bryam Vargas <hexlabsecurity at proton.me>
>
> CIFSTCon() bounds its strnlen() over the byte area with the server's
> ByteCount minus two, which for ByteCount 0 or 1 goes negative as an int
> and converts to a huge size_t.  The later subtraction wraps the __u16
> bytes_left, and that is what bounds cifs_strndup_from_utf16(): a bound of
> up to 65535 against a ~16 KB cifs_req_poolp object runs off the end of the
> slab object, and the bytes reach userspace through tcon->nativeFileSystem
> in /proc/fs/cifs/DebugData.
>
> Reject a byte area too small for what the parser consumes.  Two bytes is
> the least it can consume, and no conformant response carries fewer.  The
> new trace point is the 129th smb_eio_trace entry, which __mode(byte)
> cannot represent, so the attribute goes with it.
> ...

Applied.