Re: [PATCH v2] net: cgroup: null ptr dereference in netprio cgroup during init

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, Jul 18, 2012 at 11:34:09AM -0700, John Fastabend wrote:
> When the netprio cgroup is built in the kernel cgroup_init will call
> cgrp_create which eventually calls update_netdev_tables. This is
> being called before do_initcalls() so a null ptr dereference occurs
> on init_net.
> 
> This patch adds a check on init_net.count to verify the structure
> has been initialized. The failure was introduced here,
> 
> commit ef209f15980360f6945873df3cd710c5f62f2a3e
> Author: Gao feng <gaofeng@cn.fujitsu.com>
> Date:   Wed Jul 11 21:50:15 2012 +0000
> 
>     net: cgroup: fix access the unallocated memory in netprio cgroup
> 
> Tested with ping with netprio_cgroup as a module and built in.
> 
> [    0.256451] Initializing cgroup subsys net_prio
> [    0.269948] BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000698
> [    0.293303] IP: [<ffffffff81512e37>] cgrp_create+0x107/0x1c0
> [    0.310175] PGD 0
> [    0.316157] Oops: 0000 [#1] SMP
> [    0.325775] CPU 0
> [    0.331227] Modules linked in:
> [    0.340846]
> [    0.345264] Pid: 0, comm: swapper/0 Not tainted 3.5.0-rc7+ #1 AMD Dinar/Dinar
> [    0.366555] RIP: 0010:[<ffffffff81512e37>]  [<ffffffff81512e37>]
> cgrp_create+0x107/0x1c0
> [    0.390681] RSP: 0000:ffffffff81c01ea8  EFLAGS: 00010213
> [    0.406501] RAX: 0000000000000000 RBX: ffffffffffffff10 RCX: 0000000000000000
> [    0.427764] RDX: 0000000000000000 RSI: 0000000000000246 RDI: ffffffff81c9d840
> [    0.449026] RBP: ffffffff81c01ed8 R08: 00000000000164e0 R09: 0000000000000000
> [    0.470289] R10: ffff8804278303c0 R11: 0000000000000000 R12: 0000000000000001
> [    0.491553] R13: ffff8804278303c0 R14: ffff881036fd0700 R15: 0000000000000000
> [    0.512819] FS:  0000000000000000(0000) GS:ffff880427c00000(0000)
> knlGS:0000000000000000
> [    0.536932] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [    0.554049] CR2: 0000000000000698 CR3: 0000000001c0b000 CR4: 00000000000406b0
> [    0.575311] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [    0.596574] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [    0.617838] Process swapper/0 (pid: 0, threadinfo ffffffff81c00000, task
> ffffffff81c13420)
> [    0.642471] Stack:
> [    0.648442]  ffffffff81c01eb8 ffffffff81c9f320 ffffffff81c9f320
> ffffffff81c9f320
> [    0.670522]  ffffffff81c9f320 ffffffff81d482c0 ffffffff81c01ef8
> ffffffff81d10397
> [    0.692604]  ffffffff81e99790 0000000000000048 ffffffff81c01f18
> ffffffff81d1062e
> [    0.714687] Call Trace:
> [    0.721960]  [<ffffffff81d10397>] cgroup_init_subsys+0x51/0xdf
> [    0.739337]  [<ffffffff81d1062e>] cgroup_init+0x36/0x119
> [    0.755160]  [<ffffffff81cf5c02>] start_kernel+0x38f/0x3c4
> [    0.771501]  [<ffffffff81cf5672>] ? repair_env_string+0x5e/0x5e
> [    0.789138]  [<ffffffff81cf5356>] x86_64_start_reservations+0x131/0x135
> [    0.808849]  [<ffffffff81cf545a>] x86_64_start_kernel+0x100/0x10f
> 
> 
> Reported-by: Mark Rustad <mark.d.rustad@intel.com>
> Cc: Neil Horman <nhorman@tuxdriver.com>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Gao feng <gaofeng@cn.fujitsu.com>
> Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
> ---
> 
>  net/core/net_namespace.c  |    4 +++-
>  net/core/netprio_cgroup.c |    3 +++
>  2 files changed, 6 insertions(+), 1 deletions(-)
> 
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index dddbacb..faa33bb 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -27,7 +27,9 @@ static DEFINE_MUTEX(net_mutex);
>  LIST_HEAD(net_namespace_list);
>  EXPORT_SYMBOL_GPL(net_namespace_list);
>  
> -struct net init_net;
> +struct net init_net = {
> +	.count = ATOMIC_INIT(0),
> +};
>  EXPORT_SYMBOL(init_net);
>  
>  #define INITIAL_NET_GEN_PTRS	13 /* +1 for len +2 for rcu_head */
> diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
> index b2e9caa..e9fd7fd 100644
> --- a/net/core/netprio_cgroup.c
> +++ b/net/core/netprio_cgroup.c
> @@ -116,6 +116,9 @@ static int update_netdev_tables(void)
>  	u32 max_len;
>  	struct netprio_map *map;
>  
> +	if (!atomic_read(&init_net.count))
> +		return ret;
> +
>  	rtnl_lock();
>  	max_len = atomic_read(&max_prioidx) + 1;
>  	for_each_netdev(&init_net, dev) {
> 
> 
Acked-by: Neil Horman <nhorman@tuxdriver.com>