media: firewire: firedtv-avc: fix a buffer overflow in avc_ca_pmt()

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1958655
Upstream-status: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
CVE: CVE-2021-3542

commit 35d2969ea3c7d32aee78066b1f3cf61a0d935a4e
Author: Dan Carpenter dan.carpenter@oracle.com
Date: Mon Jun 7 17:23:48 2021 +0200

media: firewire: firedtv-avc: fix a buffer overflow in avc_ca_pmt()    

The bounds checking in avc_ca_pmt() is not strict enough.  It should    
be checking "read_pos + 4" because it's reading 5 bytes.  If the    
"es_info_length" is non-zero then it reads a 6th byte so there needs to    
be an additional check for that.    

I also added checks for the "write_pos".  I don't think these are    
required because "read_pos" and "write_pos" are tied together so    
checking one ought to be enough.  But they make the code easier to    
understand for me.  The check on write_pos is:    

	if (write_pos + 4 >= sizeof(c->operand) - 4) {    

The first "+ 4" is because we're writing 5 bytes and the last " - 4"    
is to leave space for the CRC.    

The other problem is that "length" can be invalid.  It comes from    
"data_length" in fdtv_ca_pmt().    

Cc: stable@vger.kernel.org    
Reported-by: Luo Likang <luolikang@nsfocus.com>    
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>    
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>    
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>    

Signed-off-by: Lucas Zampieri lzampier@redhat.com