Messages in this thread Patch in this message | | | Subject | Re: [PATCH net v6] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh | From | Paolo Abeni <> | Date | Tue, 12 Jul 2022 13:00:49 +0200 |
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On Mon, 2022-07-11 at 09:31 +0800, Duoming Zhou wrote: > When the link layer connection is broken, the rose->neighbour is > set to null. But rose->neighbour could be used by rose_connection() > and rose_release() later, because there is no synchronization among > them. As a result, the null-ptr-deref bugs will happen. > > One of the null-ptr-deref bugs is shown below: > > (thread 1) | (thread 2) > | rose_connect > rose_kill_by_neigh | lock_sock(sk) > spin_lock_bh(&rose_list_lock) | if (!rose->neighbour) > rose->neighbour = NULL;//(1) | > | rose->neighbour->use++;//(2) > > The rose->neighbour is set to null in position (1) and dereferenced > in position (2). > > The KASAN report triggered by POC is shown below: > > KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f] > ... > RIP: 0010:rose_connect+0x6c2/0xf30 > RSP: 0018:ffff88800ab47d60 EFLAGS: 00000206 > RAX: 0000000000000005 RBX: 000000000000002a RCX: 0000000000000000 > RDX: ffff88800ab38000 RSI: ffff88800ab47e48 RDI: ffff88800ab38309 > RBP: dffffc0000000000 R08: 0000000000000000 R09: ffffed1001567062 > R10: dfffe91001567063 R11: 1ffff11001567061 R12: 1ffff11000d17cd0 > R13: ffff8880068be680 R14: 0000000000000002 R15: 1ffff11000d17cd0 > ... > Call Trace: > <TASK> > ? __local_bh_enable_ip+0x54/0x80 > ? selinux_netlbl_socket_connect+0x26/0x30 > ? rose_bind+0x5b0/0x5b0 > __sys_connect+0x216/0x280 > __x64_sys_connect+0x71/0x80 > do_syscall_64+0x43/0x90 > entry_SYSCALL_64_after_hwframe+0x46/0xb0 > > This patch adds lock_sock() in rose_kill_by_neigh() in order to > synchronize with rose_connect() and rose_release(). Then, changing > type of 'neighbour->use' from unsigned short to atomic_t in order to > mitigate race conditions caused by holding different socket lock while > updating 'neighbour->use'. > > Meanwhile, this patch adds sock_hold() protected by rose_list_lock > that could synchronize with rose_remove_socket() in order to mitigate > UAF bug caused by lock_sock() we add. > > What's more, there is no need using rose_neigh_list_lock to protect > rose_kill_by_neigh(). Because we have already used rose_neigh_list_lock > to protect the state change of rose_neigh in rose_link_failed(), which > is well synchronized. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Signed-off-by: Duoming Zhou <duoming@zju.edu.cn> > --- > Changes in v6: > - Change sk_for_each() to sk_for_each_safe(). > - Change type of 'neighbour->use' from unsigned short to atomic_t. > > include/net/rose.h | 2 +- > net/rose/af_rose.c | 19 +++++++++++++------ > net/rose/rose_in.c | 12 ++++++------ > net/rose/rose_route.c | 24 ++++++++++++------------ > net/rose/rose_timer.c | 2 +- > 5 files changed, 33 insertions(+), 26 deletions(-) > > diff --git a/include/net/rose.h b/include/net/rose.h > index 0f0a4ce0fee..d5ddebc556d 100644 > --- a/include/net/rose.h > +++ b/include/net/rose.h > @@ -95,7 +95,7 @@ struct rose_neigh { > ax25_cb *ax25; > struct net_device *dev; > unsigned short count; > - unsigned short use; > + atomic_t use; > unsigned int number; > char restarted; > char dce_mode; > diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c > index bf2d986a6bc..54e7b76c4f3 100644 > --- a/net/rose/af_rose.c > +++ b/net/rose/af_rose.c > @@ -163,16 +163,23 @@ static void rose_remove_socket(struct sock *sk) > void rose_kill_by_neigh(struct rose_neigh *neigh) > { > struct sock *s; > + struct hlist_node *tmp; > > spin_lock_bh(&rose_list_lock); > - sk_for_each(s, &rose_list) { > + sk_for_each_safe(s, tmp, &rose_list) { > struct rose_sock *rose = rose_sk(s); > > + sock_hold(s); > + spin_unlock_bh(&rose_list_lock); > + lock_sock(s); > if (rose->neighbour == neigh) { > rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0); > - rose->neighbour->use--; > + atomic_dec(&rose->neighbour->use); > rose->neighbour = NULL; > } > + release_sock(s); > + sock_put(s);
I'm sorry, this does not work. At this point both 's' and 'tmp' sockets can be freed and reused. Both iterators are not valid anymore when you acquire the 'rose_list_lock' later.
I really think you should resort to something similar to the following (completelly untested, just to give an idea). In any case it would be better to split this change in 2 separate patches: the first patch replaces 'int use;' with an antomic_t and the 2nd one addresses the race you describe above.
--- diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c index bf2d986a6bc3..27b1027aaedf 100644 --- a/net/rose/af_rose.c +++ b/net/rose/af_rose.c @@ -156,25 +156,45 @@ static void rose_remove_socket(struct sock *sk) spin_unlock_bh(&rose_list_lock); } +static DEFINE_MUTEX(kill_lock); + /* * Kill all bound sockets on a broken link layer connection to a * particular neighbour. */ void rose_kill_by_neigh(struct rose_neigh *neigh) { - struct sock *s; + HLIST_HEAD(rose_list_copy); + struct sock *s, *tmp; + + mutex_lock(&kill_lock); spin_lock_bh(&rose_list_lock); sk_for_each(s, &rose_list) { + sock_hold(s); + /* sk_bind_node is apparently unused by rose. Alternatively + * you can add another hlist_node to rose_sock and use it here + */ + sk_add_bind_node(s, &rose_list_copy); + } + spin_unlock_bh(&rose_list_lock); + + hlist_for_each_entry_safe(s, tmp, &rose_list_copy, sk_bind_node) { struct rose_sock *rose = rose_sk(s); + __sk_del_bind_node(s); + lock_sock(s); if (rose->neighbour == neigh) { rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0); - rose->neighbour->use--; + atomic_dec(&rose->neighbour->use); rose->neighbour = NULL; } + release_sock(s); + + sock_put(s); } - spin_unlock_bh(&rose_list_lock); + + mutex_unlock(&kill_lock); } /* --- /P
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