Re: [PATCH net v6] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh
From: Paolo Abeni <pabeni@redhat.com>
Date: 2022-07-12 11:01:16
Also in:
linux-hams, lkml
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
On Mon, 2022-07-11 at 09:31 +0800, Duoming Zhou wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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