CVS commit: src/sys/dev/usb

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

Module Name:    src
Committed By:   riastradh
Date:           Fri Aug 12 11:25:46 UTC 2022

Modified Files:
        src/sys/dev/usb: usbnet.c

Log Message:
usbnet(9): Fix mbuf alignment and narrow bounds check.

In usbnet.c rev. 1.16, usbnet_newbuf was first passed a buffer length
to verify it fits within MCLBYTES.  It also changed m_adj to go
before, not after, setting m_len and m_pkthdr.len -- which had the
effect of making the m_adj a no-op, because after MGETHDR the mbuf
has zero length and m_adj stops at the length of the mbuf, so nothing
was aligned as intended.

To make this aligned as intended, we require the buffer length to be
_below_ MCLBYTES, by ETHER_ALIGN, so there's room for the ethernet
header in a maximum-length payload.  Once we do that, it is safe to
initialize m_len = m_pkthdr.len = ETHER_ALIGN + buflen, which is
below the actual size of the mbuf (MHLEN or MCLBYTES, depending), and
_then_ do m_adj to align the pointer.


To generate a diff of this commit:
cvs rdiff -u -r1.95 -r1.96 src/sys/dev/usb/usbnet.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.