| Message ID | 1484958086-6151-3-git-send-email-rshearma@brocade.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Robert Shearman <rshearma@brocade.com> Date: Sat, 21 Jan 2017 00:21:26 +0000 > @@ -115,8 +115,12 @@ int lwtunnel_build_state(struct net_device *dev, u16 encap_type, > ret = -EOPNOTSUPP; > rcu_read_lock(); Here 'ret' equals -EOPNOTSUPP > ops = rcu_dereference(lwtun_encaps[encap_type]); > - if (likely(ops && ops->build_state)) > - ret = ops->build_state(dev, encap, family, cfg, lws); > + if (likely(ops)) { > + if (likely(try_module_get(ops->owner) && ops->build_state)) > + ret = ops->build_state(dev, encap, family, cfg, lws); > + if (ret) > + module_put(ops->owner); If try_module_get() fails, 'ret' will still be -EOPNOTSUPP and we will module_put() on a module we did not grab a reference to. I think you need to adjust the logic here. You only want to 'put' if try_module_get() succeeds and ->build_state() returns an error.
On 23/01/17 20:42, David Miller wrote: > From: Robert Shearman <rshearma@brocade.com> > Date: Sat, 21 Jan 2017 00:21:26 +0000 > >> @@ -115,8 +115,12 @@ int lwtunnel_build_state(struct net_device *dev, u16 encap_type, >> ret = -EOPNOTSUPP; >> rcu_read_lock(); > > Here 'ret' equals -EOPNOTSUPP > >> ops = rcu_dereference(lwtun_encaps[encap_type]); >> - if (likely(ops && ops->build_state)) >> - ret = ops->build_state(dev, encap, family, cfg, lws); >> + if (likely(ops)) { >> + if (likely(try_module_get(ops->owner) && ops->build_state)) >> + ret = ops->build_state(dev, encap, family, cfg, lws); >> + if (ret) >> + module_put(ops->owner); > > If try_module_get() fails, 'ret' will still be -EOPNOTSUPP and we will > module_put() on a module we did not grab a reference to. > > I think you need to adjust the logic here. You only want to 'put' if > try_module_get() succeeds and ->build_state() returns an error. Indeed, good point. Will address in a v3 shortly. Thanks, Rob
diff --git a/net/core/lwtunnel.c b/net/core/lwtunnel.c index 47b1dd65947b..ebfaffaa777b 100644 --- a/net/core/lwtunnel.c +++ b/net/core/lwtunnel.c @@ -115,8 +115,12 @@ int lwtunnel_build_state(struct net_device *dev, u16 encap_type, ret = -EOPNOTSUPP; rcu_read_lock(); ops = rcu_dereference(lwtun_encaps[encap_type]); - if (likely(ops && ops->build_state)) - ret = ops->build_state(dev, encap, family, cfg, lws); + if (likely(ops)) { + if (likely(try_module_get(ops->owner) && ops->build_state)) + ret = ops->build_state(dev, encap, family, cfg, lws); + if (ret) + module_put(ops->owner); + } rcu_read_unlock(); return ret; @@ -194,6 +198,7 @@ void lwtstate_free(struct lwtunnel_state *lws) } else { kfree(lws); } + module_put(ops->owner); } EXPORT_SYMBOL(lwtstate_free);
When attempting to free lwtunnel state after the module for the encap has been unloaded an oops occurs: BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 IP: lwtstate_free+0x18/0x40 [..] task: ffff88003e372380 task.stack: ffffc900001fc000 RIP: 0010:lwtstate_free+0x18/0x40 RSP: 0018:ffff88003fd83e88 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff88002bbb3380 RCX: ffff88000c91a300 [..] Call Trace: <IRQ> free_fib_info_rcu+0x195/0x1a0 ? rt_fibinfo_free+0x50/0x50 rcu_process_callbacks+0x2d3/0x850 ? rcu_process_callbacks+0x296/0x850 __do_softirq+0xe4/0x4cb irq_exit+0xb0/0xc0 smp_apic_timer_interrupt+0x3d/0x50 apic_timer_interrupt+0x93/0xa0 [..] Code: e8 6e c6 fc ff 89 d8 5b 5d c3 bb de ff ff ff eb f4 66 90 66 66 66 66 90 55 48 89 e5 53 0f b7 07 48 89 fb 48 8b 04 c5 00 81 d5 81 <48> 8b 40 08 48 85 c0 74 13 ff d0 48 8d 7b 20 be 20 00 00 00 e8 The problem is after the module for the encap is unloaded the corresponding ops is removed and thus is NULL here. Modules implementing lwtunnel ops should not be allowed to unload while there is state alive using those ops, so grab the module reference for the ops on creating lwtunnel state and of course release the reference when freeing the state. Fixes: 1104d9ba443a ("lwtunnel: Add destroy state operation") Signed-off-by: Robert Shearman <rshearma@brocade.com> --- net/core/lwtunnel.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)