[Drbd-dev] [PATCH v2] drbd: Fix kernel_sendmsg() usage - potential NULL deref

[Al Viro]

On Wed, Nov 09, 2016 at 10:52:58PM +0100, Lars Ellenberg wrote:

> This should go into 4.9,
> and into all stable branches since and including v4.0,
> which is the first to contain the exposing change.
> 
> It is correct for all stable branches older than that as well
> (which contain the DRBD driver; which is 2.6.33 and up).
> 
> It requires a small "conflict" resolution for v4.4 and earlier, with v4.5
> we dropped the comment block immediately preceding the kernel_sendmsg().

ACK.  I'll rebase commit 7a4992299554 ([drbd] use sock_sendmsg()) on top
of that as soon as it hits the mainline.  For conspiracy theorists out
there (hi, Brad) - that commit (killing the modifications of iovec and
reinitializing msg->iov_iter; just set it once and let sendmsg() update
it in normal fashion) had been sitting around since late 2014.  It happened
to fix the bug in question, without a single line refering to that in commit
message.  Reason: I had completely missed the problem; intent of that
loop had been obvious and replacement had obviously done what was intended
there.  What I had failed to spot was that the code in there did *not*
match that intent.  Replacement does.  And unlike the minimal fix (either
version) it doesn't belong in -stable.