[PATCH 3.16 350/366] ppp: fix lockdep splat in ppp_dev_uninit()

Ben Hutchings
2018-10-14T23:11:52Z

From: Guillaume Nault <g.nault@alphalink.fr>

commit 58a89ecaca53736aa465170530acea4f8be34ab4 upstream.

ppp_dev_uninit() locks all_ppp_mutex while under rtnl mutex protection.
ppp_create_interface() must then lock these mutexes in that same order
to avoid possible deadlock.

[ 120.880011] ======================================================
[ 120.880011] [ INFO: possible circular locking dependency detected ]
[ 120.880011] 4.2.0 #1 Not tainted
[ 120.880011] -------------------------------------------------------
[ 120.880011] ppp-apitest/15827 is trying to acquire lock:
[ 120.880011] (&pn->all_ppp_mutex){+.+.+.}, at: [<ffffffffa0145f56>] ppp_dev_uninit+0x64/0xb0 [ppp_generic]
[ 120.880011]
[ 120.880011] but task is already holding lock:
[ 120.880011] (rtnl_mutex){+.+.+.}, at: [<ffffffff812e4255>] rtnl_lock+0x12/0x14
[ 120.880011]
[ 120.880011] which lock already depends on the new lock.
[ 120.880011]
[ 120.880011]
[ 120.880011] the existing dependency chain (in reverse order) is:
[ 120.880011]
[ 120.880011] -> #1 (rtnl_mutex){+.+.+.}:
[ 120.880011] [<ffffffff81073a6f>] lock_acquire+0xcf/0x10e
[ 120.880011] [<ffffffff813ab18a>] mutex_lock_nested+0x56/0x341
[ 120.880011] [<ffffffff812e4255>] rtnl_lock+0x12/0x14
[ 120.880011] [<ffffffff812d9d94>] register_netdev+0x11/0x27
[ 120.880011] [<ffffffffa0147b17>] ppp_ioctl+0x289/0xc98 [ppp_generic]
[ 120.880011] [<ffffffff8113b367>] do_vfs_ioctl+0x4ea/0x532
[ 120.880011] [<ffffffff8113b3fd>] SyS_ioctl+0x4e/0x7d
[ 120.880011] [<ffffffff813ad7d7>] entry_SYSCALL_64_fastpath+0x12/0x6f
[ 120.880011]
[ 120.880011] -> #0 (&pn->all_ppp_mutex){+.+.+.}:
[ 120.880011] [<ffffffff8107334e>] __lock_acquire+0xb07/0xe76
[ 120.880011] [<ffffffff81073a6f>] lock_acquire+0xcf/0x10e
[ 120.880011] [<ffffffff813ab18a>] mutex_lock_nested+0x56/0x341
[ 120.880011] [<ffffffffa0145f56>] ppp_dev_uninit+0x64/0xb0 [ppp_generic]
[ 120.880011] [<ffffffff812d5263>] rollback_registered_many+0x19e/0x252
[ 120.880011] [<ffffffff812d5381>] rollback_registered+0x29/0x38
[ 120.880011] [<ffffffff812d53fa>] unregister_netdevice_queue+0x6a/0x77
[ 120.880011] [<ffffffffa0146a94>] ppp_release+0x42/0x79 [ppp_generic]
[ 120.880011] [<ffffffff8112d9f6>] __fput+0xec/0x192
[ 120.880011] [<ffffffff8112dacc>] ____fput+0x9/0xb
[ 120.880011] [<ffffffff8105447a>] task_work_run+0x66/0x80
[ 120.880011] [<ffffffff81001801>] prepare_exit_to_usermode+0x8c/0xa7
[ 120.880011] [<ffffffff81001900>] syscall_return_slowpath+0xe4/0x104
[ 120.880011] [<ffffffff813ad931>] int_ret_from_sys_call+0x25/0x9f
[ 120.880011]
[ 120.880011] other info that might help us debug this:
[ 120.880011]
[ 120.880011] Possible unsafe locking scenario:
[ 120.880011]
[ 120.880011] CPU0 CPU1
[ 120.880011] ---- ----
[ 120.880011] lock(rtnl_mutex);
[ 120.880011] lock(&pn->all_ppp_mutex);
[ 120.880011] lock(rtnl_mutex);
[ 120.880011] lock(&pn->all_ppp_mutex);
[ 120.880011]
[ 120.880011] *** DEADLOCK ***

Fixes: 8cb775bc0a34 ("ppp: fix device unregistration upon netns deletion")
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/net/ppp/ppp_generic.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -2736,6 +2736,7 @@ static struct ppp *ppp_create_interface(
*/
dev_net_set(dev, net);

+ rtnl_lock();
mutex_lock(&pn->all_ppp_mutex);

if (unit < 0) {
@@ -2766,7 +2767,7 @@ static struct ppp *ppp_create_interface(
ppp->file.index = unit;
sprintf(dev->name, "ppp%d", unit);

- ret = register_netdev(dev);
+ ret = register_netdevice(dev);
if (ret != 0) {
unit_put(&pn->units_idr, unit);
netdev_err(ppp->dev, "PPP: couldn't register device %s (%d)\n",
@@ -2778,6 +2779,7 @@ static struct ppp *ppp_create_interface(

atomic_inc(&ppp_unit_count);
mutex_unlock(&pn->all_ppp_mutex);
+ rtnl_unlock();

*retp = 0;
return ppp;