This is a note to let you know that I've just added the patch titled
ppp: prevent unregistered channels from connecting to PPP units
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: ppp-prevent-unregistered-channels-from-connecting-to-ppp-units.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Thu Mar 8 06:55:02 PST 2018
From: Guillaume Nault g.nault@alphalink.fr Date: Fri, 2 Mar 2018 18:41:16 +0100 Subject: ppp: prevent unregistered channels from connecting to PPP units
From: Guillaume Nault g.nault@alphalink.fr
[ Upstream commit 77f840e3e5f09c6d7d727e85e6e08276dd813d11 ]
PPP units don't hold any reference on the channels connected to it. It is the channel's responsibility to ensure that it disconnects from its unit before being destroyed. In practice, this is ensured by ppp_unregister_channel() disconnecting the channel from the unit before dropping a reference on the channel.
However, it is possible for an unregistered channel to connect to a PPP unit: register a channel with ppp_register_net_channel(), attach a /dev/ppp file to it with ioctl(PPPIOCATTCHAN), unregister the channel with ppp_unregister_channel() and finally connect the /dev/ppp file to a PPP unit with ioctl(PPPIOCCONNECT).
Once in this situation, the channel is only held by the /dev/ppp file, which can be released at anytime and free the channel without letting the parent PPP unit know. Then the ppp structure ends up with dangling pointers in its ->channels list.
Prevent this scenario by forbidding unregistered channels from connecting to PPP units. This maintains the code logic by keeping ppp_unregister_channel() responsible from disconnecting the channel if necessary and avoids modification on the reference counting mechanism.
This issue seems to predate git history (successfully reproduced on Linux 2.6.26 and earlier PPP commits are unrelated).
Signed-off-by: Guillaume Nault g.nault@alphalink.fr Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/ppp/ppp_generic.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -3157,6 +3157,15 @@ ppp_connect_channel(struct channel *pch, goto outl;
ppp_lock(ppp); + spin_lock_bh(&pch->downl); + if (!pch->chan) { + /* Don't connect unregistered channels */ + spin_unlock_bh(&pch->downl); + ppp_unlock(ppp); + ret = -ENOTCONN; + goto outl; + } + spin_unlock_bh(&pch->downl); if (pch->file.hdrlen > ppp->file.hdrlen) ppp->file.hdrlen = pch->file.hdrlen; hdrlen = pch->file.hdrlen + 2; /* for protocol bytes */
Patches currently in stable-queue which might be from g.nault@alphalink.fr are
queue-4.9/ppp-prevent-unregistered-channels-from-connecting-to-ppp-units.patch