path: root/drivers/net/ppp
diff options
authorEric Biggers <ebiggers@google.com>2018-05-23 14:37:38 -0700
committerDavid S. Miller <davem@davemloft.net>2018-05-24 22:55:07 -0400
commitaf8d3c7c001ae7df1ed2b2715f058113efc86187 (patch)
tree1575c5be02826394ccef3639ab8ec7c033eec5b8 /drivers/net/ppp
parentipv4: remove warning in ip_recv_error (diff)
ppp: remove the PPPIOCDETACH ioctl
The PPPIOCDETACH ioctl effectively tries to "close" the given ppp file before f_count has reached 0, which is fundamentally a bad idea. It does check 'f_count < 2', which excludes concurrent operations on the file since they would only be possible with a shared fd table, in which case each fdget() would take a file reference. However, it fails to account for the fact that even with 'f_count == 1' the file can still be linked into epoll instances. As reported by syzbot, this can trivially be used to cause a use-after-free. Yet, the only known user of PPPIOCDETACH is pppd versions older than ppp-2.4.2, which was released almost 15 years ago (November 2003). Also, PPPIOCDETACH apparently stopped working reliably at around the same time, when the f_count check was added to the kernel, e.g. see https://lkml.org/lkml/2002/12/31/83. Also, the current 'f_count < 2' check makes PPPIOCDETACH only work in single-threaded applications; it always fails if called from a multithreaded application. All pppd versions released in the last 15 years just close() the file descriptor instead. Therefore, instead of hacking around this bug by exporting epoll internals to modules, and probably missing other related bugs, just remove the PPPIOCDETACH ioctl and see if anyone actually notices. Leave a stub in place that prints a one-time warning and returns EINVAL. Reported-by: syzbot+16363c99d4134717c05b@syzkaller.appspotmail.com Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Eric Biggers <ebiggers@google.com> Acked-by: Paul Mackerras <paulus@ozlabs.org> Reviewed-by: Guillaume Nault <g.nault@alphalink.fr> Tested-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, 5 insertions, 22 deletions
diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index dc7c7ec43202..02ad03a2fab7 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -605,30 +605,13 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
if (cmd == PPPIOCDETACH) {
- * We have to be careful here... if the file descriptor
- * has been dup'd, we could have another process in the
- * middle of a poll using the same file *, so we had
- * better not free the interface data structures -
- * instead we fail the ioctl. Even in this case, we
- * shut down the interface if we are the owner of it.
- * Actually, we should get rid of PPPIOCDETACH, userland
- * (i.e. pppd) could achieve the same effect by closing
- * this fd and reopening /dev/ppp.
+ * PPPIOCDETACH is no longer supported as it was heavily broken,
+ * and is only known to have been used by pppd older than
+ * ppp-2.4.2 (released November 2003).
+ pr_warn_once("%s (%d) used obsolete PPPIOCDETACH ioctl\n",
+ current->comm, current->pid);
err = -EINVAL;
- if (pf->kind == INTERFACE) {
- ppp = PF_TO_PPP(pf);
- rtnl_lock();
- if (file == ppp->owner)
- unregister_netdevice(ppp->dev);
- rtnl_unlock();
- }
- if (atomic_long_read(&file->f_count) < 2) {
- ppp_release(NULL, file);
- err = 0;
- } else
- pr_warn("PPPIOCDETACH file->f_count=%ld\n",
- atomic_long_read(&file->f_count));
goto out;