path: root/drivers/net/ppp
diff options
authorGuillaume Nault <g.nault@alphalink.fr>2018-03-02 18:41:16 +0100
committerDavid S. Miller <davem@davemloft.net>2018-03-04 18:43:44 -0500
commit77f840e3e5f09c6d7d727e85e6e08276dd813d11 (patch)
tree07fea4af406de10219354204cc0d0351bb288115 /drivers/net/ppp
parenttc-testing: skbmod: fix match value of ethertype (diff)
ppp: prevent unregistered channels from connecting to PPP units
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>
Diffstat (limited to 'drivers/net/ppp')
1 files changed, 9 insertions, 0 deletions
diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index 255a5def56e9..fa2a9bdd1866 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -3161,6 +3161,15 @@ ppp_connect_channel(struct channel *pch, int unit)
goto outl;
+ 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 */