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edumazetgregkh
edumazet
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gregkh
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ax25: rcu protect dev->ax25_ptr
[ Upstream commit 95fc45d ] syzbot found a lockdep issue [1]. We should remove ax25 RTNL dependency in ax25_setsockopt() This should also fix a variety of possible UAF in ax25. [1] WARNING: possible circular locking dependency detected 6.13.0-rc3-syzkaller-00762-g9268abe611b0 #0 Not tainted ------------------------------------------------------ syz.5.1818/12806 is trying to acquire lock: ffffffff8fcb3988 (rtnl_mutex){+.+.}-{4:4}, at: ax25_setsockopt+0xa55/0xe90 net/ax25/af_ax25.c:680 but task is already holding lock: ffff8880617ac258 (sk_lock-AF_AX25){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1618 [inline] ffff8880617ac258 (sk_lock-AF_AX25){+.+.}-{0:0}, at: ax25_setsockopt+0x209/0xe90 net/ax25/af_ax25.c:574 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (sk_lock-AF_AX25){+.+.}-{0:0}: lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849 lock_sock_nested+0x48/0x100 net/core/sock.c:3642 lock_sock include/net/sock.h:1618 [inline] ax25_kill_by_device net/ax25/af_ax25.c:101 [inline] ax25_device_event+0x24d/0x580 net/ax25/af_ax25.c:146 notifier_call_chain+0x1a5/0x3f0 kernel/notifier.c:85 __dev_notify_flags+0x207/0x400 dev_change_flags+0xf0/0x1a0 net/core/dev.c:9026 dev_ifsioc+0x7c8/0xe70 net/core/dev_ioctl.c:563 dev_ioctl+0x719/0x1340 net/core/dev_ioctl.c:820 sock_do_ioctl+0x240/0x460 net/socket.c:1234 sock_ioctl+0x626/0x8e0 net/socket.c:1339 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:906 [inline] __se_sys_ioctl+0xf5/0x170 fs/ioctl.c:892 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #0 (rtnl_mutex){+.+.}-{4:4}: check_prev_add kernel/locking/lockdep.c:3161 [inline] check_prevs_add kernel/locking/lockdep.c:3280 [inline] validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5226 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849 __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0x1ac/0xee0 kernel/locking/mutex.c:735 ax25_setsockopt+0xa55/0xe90 net/ax25/af_ax25.c:680 do_sock_setsockopt+0x3af/0x720 net/socket.c:2324 __sys_setsockopt net/socket.c:2349 [inline] __do_sys_setsockopt net/socket.c:2355 [inline] __se_sys_setsockopt net/socket.c:2352 [inline] __x64_sys_setsockopt+0x1ee/0x280 net/socket.c:2352 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(sk_lock-AF_AX25); lock(rtnl_mutex); lock(sk_lock-AF_AX25); lock(rtnl_mutex); *** DEADLOCK *** 1 lock held by syz.5.1818/12806: #0: ffff8880617ac258 (sk_lock-AF_AX25){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1618 [inline] #0: ffff8880617ac258 (sk_lock-AF_AX25){+.+.}-{0:0}, at: ax25_setsockopt+0x209/0xe90 net/ax25/af_ax25.c:574 stack backtrace: CPU: 1 UID: 0 PID: 12806 Comm: syz.5.1818 Not tainted 6.13.0-rc3-syzkaller-00762-g9268abe611b0 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120 print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2074 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2206 check_prev_add kernel/locking/lockdep.c:3161 [inline] check_prevs_add kernel/locking/lockdep.c:3280 [inline] validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5226 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849 __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0x1ac/0xee0 kernel/locking/mutex.c:735 ax25_setsockopt+0xa55/0xe90 net/ax25/af_ax25.c:680 do_sock_setsockopt+0x3af/0x720 net/socket.c:2324 __sys_setsockopt net/socket.c:2349 [inline] __do_sys_setsockopt net/socket.c:2355 [inline] __se_sys_setsockopt net/socket.c:2352 [inline] __x64_sys_setsockopt+0x1ee/0x280 net/socket.c:2352 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f7b62385d29 Fixes: c433570 ("ax25: fix a use-after-free in ax25_fillin_cb()") Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com> Link: https://patch.msgid.link/20250103210514.87290-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
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-20
lines changed

7 files changed

+35
-20
lines changed

‎include/linux/netdevice.h‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2217,7 +2217,7 @@ struct net_device {
22172217
void *atalk_ptr;
22182218
#endif
22192219
#if IS_ENABLED(CONFIG_AX25)
2220-
void *ax25_ptr;
2220+
struct ax25_dev __rcu *ax25_ptr;
22212221
#endif
22222222
#if IS_ENABLED(CONFIG_CFG80211)
22232223
struct wireless_dev *ieee80211_ptr;

‎include/net/ax25.h‎

Lines changed: 5 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -229,6 +229,7 @@ typedef struct ax25_dev {
229229
#endif
230230
refcount_t refcount;
231231
bool device_up;
232+
struct rcu_head rcu;
232233
} ax25_dev;
233234

234235
typedef struct ax25_cb {
@@ -288,9 +289,8 @@ static inline void ax25_dev_hold(ax25_dev *ax25_dev)
288289

289290
static inline void ax25_dev_put(ax25_dev *ax25_dev)
290291
{
291-
if (refcount_dec_and_test(&ax25_dev->refcount)) {
292-
kfree(ax25_dev);
293-
}
292+
if (refcount_dec_and_test(&ax25_dev->refcount))
293+
kfree_rcu(ax25_dev, rcu);
294294
}
295295
static inline __be16 ax25_type_trans(struct sk_buff *skb, struct net_device *dev)
296296
{
@@ -333,9 +333,9 @@ void ax25_digi_invert(const ax25_digi *, ax25_digi *);
333333
extern spinlock_t ax25_dev_lock;
334334

335335
#if IS_ENABLED(CONFIG_AX25)
336-
static inline ax25_dev *ax25_dev_ax25dev(struct net_device *dev)
336+
static inline ax25_dev *ax25_dev_ax25dev(const struct net_device *dev)
337337
{
338-
return dev->ax25_ptr;
338+
return rcu_dereference_rtnl(dev->ax25_ptr);
339339
}
340340
#endif
341341

‎net/ax25/af_ax25.c‎

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -467,7 +467,7 @@ static int ax25_ctl_ioctl(const unsigned int cmd, void __user *arg)
467467
goto out_put;
468468
}
469469

470-
static void ax25_fillin_cb_from_dev(ax25_cb *ax25, ax25_dev *ax25_dev)
470+
static void ax25_fillin_cb_from_dev(ax25_cb *ax25, const ax25_dev *ax25_dev)
471471
{
472472
ax25->rtt = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_T1]) / 2;
473473
ax25->t1 = msecs_to_jiffies(ax25_dev->values[AX25_VALUES_T1]);
@@ -677,22 +677,22 @@ static int ax25_setsockopt(struct socket *sock, int level, int optname,
677677
break;
678678
}
679679

680-
rtnl_lock();
681-
dev = __dev_get_by_name(&init_net, devname);
680+
rcu_read_lock();
681+
dev = dev_get_by_name_rcu(&init_net, devname);
682682
if (!dev) {
683-
rtnl_unlock();
683+
rcu_read_unlock();
684684
res = -ENODEV;
685685
break;
686686
}
687687

688688
ax25->ax25_dev = ax25_dev_ax25dev(dev);
689689
if (!ax25->ax25_dev) {
690-
rtnl_unlock();
690+
rcu_read_unlock();
691691
res = -ENODEV;
692692
break;
693693
}
694694
ax25_fillin_cb(ax25, ax25->ax25_dev);
695-
rtnl_unlock();
695+
rcu_read_unlock();
696696
break;
697697

698698
default:

‎net/ax25/ax25_dev.c‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -87,7 +87,7 @@ void ax25_dev_device_up(struct net_device *dev)
8787

8888
spin_lock_bh(&ax25_dev_lock);
8989
list_add(&ax25_dev->list, &ax25_dev_list);
90-
dev->ax25_ptr = ax25_dev;
90+
rcu_assign_pointer(dev->ax25_ptr, ax25_dev);
9191
spin_unlock_bh(&ax25_dev_lock);
9292

9393
ax25_register_dev_sysctl(ax25_dev);
@@ -122,7 +122,7 @@ void ax25_dev_device_down(struct net_device *dev)
122122
}
123123
}
124124

125-
dev->ax25_ptr = NULL;
125+
RCU_INIT_POINTER(dev->ax25_ptr, NULL);
126126
spin_unlock_bh(&ax25_dev_lock);
127127
netdev_put(dev, &ax25_dev->dev_tracker);
128128
ax25_dev_put(ax25_dev);

‎net/ax25/ax25_ip.c‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -122,6 +122,7 @@ netdev_tx_t ax25_ip_xmit(struct sk_buff *skb)
122122
if (dev == NULL)
123123
dev = skb->dev;
124124

125+
rcu_read_lock();
125126
if ((ax25_dev = ax25_dev_ax25dev(dev)) == NULL) {
126127
kfree_skb(skb);
127128
goto put;
@@ -202,7 +203,7 @@ netdev_tx_t ax25_ip_xmit(struct sk_buff *skb)
202203
ax25_queue_xmit(skb, dev);
203204

204205
put:
205-
206+
rcu_read_unlock();
206207
ax25_route_lock_unuse();
207208
return NETDEV_TX_OK;
208209
}

‎net/ax25/ax25_out.c‎

Lines changed: 17 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -39,10 +39,14 @@ ax25_cb *ax25_send_frame(struct sk_buff *skb, int paclen, const ax25_address *sr
3939
* specified.
4040
*/
4141
if (paclen == 0) {
42-
if ((ax25_dev = ax25_dev_ax25dev(dev)) == NULL)
42+
rcu_read_lock();
43+
ax25_dev = ax25_dev_ax25dev(dev);
44+
if (!ax25_dev) {
45+
rcu_read_unlock();
4346
return NULL;
44-
47+
}
4548
paclen = ax25_dev->values[AX25_VALUES_PACLEN];
49+
rcu_read_unlock();
4650
}
4751

4852
/*
@@ -53,13 +57,19 @@ ax25_cb *ax25_send_frame(struct sk_buff *skb, int paclen, const ax25_address *sr
5357
return ax25; /* It already existed */
5458
}
5559

56-
if ((ax25_dev = ax25_dev_ax25dev(dev)) == NULL)
60+
rcu_read_lock();
61+
ax25_dev = ax25_dev_ax25dev(dev);
62+
if (!ax25_dev) {
63+
rcu_read_unlock();
5764
return NULL;
65+
}
5866

59-
if ((ax25 = ax25_create_cb()) == NULL)
67+
if ((ax25 = ax25_create_cb()) == NULL) {
68+
rcu_read_unlock();
6069
return NULL;
61-
70+
}
6271
ax25_fillin_cb(ax25, ax25_dev);
72+
rcu_read_unlock();
6373

6474
ax25->source_addr = *src;
6575
ax25->dest_addr = *dest;
@@ -358,7 +368,9 @@ void ax25_queue_xmit(struct sk_buff *skb, struct net_device *dev)
358368
{
359369
unsigned char *ptr;
360370

371+
rcu_read_lock();
361372
skb->protocol = ax25_type_trans(skb, ax25_fwd_dev(dev));
373+
rcu_read_unlock();
362374

363375
ptr = skb_push(skb, 1);
364376
*ptr = 0x00; /* KISS */

‎net/ax25/ax25_route.c‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -406,6 +406,7 @@ int ax25_rt_autobind(ax25_cb *ax25, ax25_address *addr)
406406
ax25_route_lock_unuse();
407407
return -EHOSTUNREACH;
408408
}
409+
rcu_read_lock();
409410
if ((ax25->ax25_dev = ax25_dev_ax25dev(ax25_rt->dev)) == NULL) {
410411
err = -EHOSTUNREACH;
411412
goto put;
@@ -442,6 +443,7 @@ int ax25_rt_autobind(ax25_cb *ax25, ax25_address *addr)
442443
}
443444

444445
put:
446+
rcu_read_unlock();
445447
ax25_route_lock_unuse();
446448
return err;
447449
}

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