Patch "ipv6: fix possible race in __fib6_drop_pcpu_from()" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    ipv6: fix possible race in __fib6_drop_pcpu_from()

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ipv6-fix-possible-race-in-__fib6_drop_pcpu_from.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 93ff2919f7c20c1e9ab04e08feb0e98c64f21e6d
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Tue Jun 4 19:35:49 2024 +0000

    ipv6: fix possible race in __fib6_drop_pcpu_from()
    
    [ Upstream commit b01e1c030770ff3b4fe37fc7cc6bca03f594133f ]
    
    syzbot found a race in __fib6_drop_pcpu_from() [1]
    
    If compiler reads more than once (*ppcpu_rt),
    second read could read NULL, if another cpu clears
    the value in rt6_get_pcpu_route().
    
    Add a READ_ONCE() to prevent this race.
    
    Also add rcu_read_lock()/rcu_read_unlock() because
    we rely on RCU protection while dereferencing pcpu_rt.
    
    [1]
    
    Oops: general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] PREEMPT SMP KASAN PTI
    KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097]
    CPU: 0 PID: 7543 Comm: kworker/u8:17 Not tainted 6.10.0-rc1-syzkaller-00013-g2bfcfd584ff5 #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
    Workqueue: netns cleanup_net
     RIP: 0010:__fib6_drop_pcpu_from.part.0+0x10a/0x370 net/ipv6/ip6_fib.c:984
    Code: f8 48 c1 e8 03 80 3c 28 00 0f 85 16 02 00 00 4d 8b 3f 4d 85 ff 74 31 e8 74 a7 fa f7 49 8d bf 90 00 00 00 48 89 f8 48 c1 e8 03 <80> 3c 28 00 0f 85 1e 02 00 00 49 8b 87 90 00 00 00 48 8b 0c 24 48
    RSP: 0018:ffffc900040df070 EFLAGS: 00010206
    RAX: 0000000000000012 RBX: 0000000000000001 RCX: ffffffff89932e16
    RDX: ffff888049dd1e00 RSI: ffffffff89932d7c RDI: 0000000000000091
    RBP: dffffc0000000000 R08: 0000000000000005 R09: 0000000000000007
    R10: 0000000000000001 R11: 0000000000000006 R12: ffff88807fa080b8
    R13: fffffbfff1a9a07d R14: ffffed100ff41022 R15: 0000000000000001
    FS:  0000000000000000(0000) GS:ffff8880b9200000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000001b32c26000 CR3: 000000005d56e000 CR4: 00000000003526f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
     <TASK>
      __fib6_drop_pcpu_from net/ipv6/ip6_fib.c:966 [inline]
      fib6_drop_pcpu_from net/ipv6/ip6_fib.c:1027 [inline]
      fib6_purge_rt+0x7f2/0x9f0 net/ipv6/ip6_fib.c:1038
      fib6_del_route net/ipv6/ip6_fib.c:1998 [inline]
      fib6_del+0xa70/0x17b0 net/ipv6/ip6_fib.c:2043
      fib6_clean_node+0x426/0x5b0 net/ipv6/ip6_fib.c:2205
      fib6_walk_continue+0x44f/0x8d0 net/ipv6/ip6_fib.c:2127
      fib6_walk+0x182/0x370 net/ipv6/ip6_fib.c:2175
      fib6_clean_tree+0xd7/0x120 net/ipv6/ip6_fib.c:2255
      __fib6_clean_all+0x100/0x2d0 net/ipv6/ip6_fib.c:2271
      rt6_sync_down_dev net/ipv6/route.c:4906 [inline]
      rt6_disable_ip+0x7ed/0xa00 net/ipv6/route.c:4911
      addrconf_ifdown.isra.0+0x117/0x1b40 net/ipv6/addrconf.c:3855
      addrconf_notify+0x223/0x19e0 net/ipv6/addrconf.c:3778
      notifier_call_chain+0xb9/0x410 kernel/notifier.c:93
      call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:1992
      call_netdevice_notifiers_extack net/core/dev.c:2030 [inline]
      call_netdevice_notifiers net/core/dev.c:2044 [inline]
      dev_close_many+0x333/0x6a0 net/core/dev.c:1585
      unregister_netdevice_many_notify+0x46d/0x19f0 net/core/dev.c:11193
      unregister_netdevice_many net/core/dev.c:11276 [inline]
      default_device_exit_batch+0x85b/0xae0 net/core/dev.c:11759
      ops_exit_list+0x128/0x180 net/core/net_namespace.c:178
      cleanup_net+0x5b7/0xbf0 net/core/net_namespace.c:640
      process_one_work+0x9fb/0x1b60 kernel/workqueue.c:3231
      process_scheduled_works kernel/workqueue.c:3312 [inline]
      worker_thread+0x6c8/0xf70 kernel/workqueue.c:3393
      kthread+0x2c1/0x3a0 kernel/kthread.c:389
      ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
      ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
    
    Fixes: d52d3997f843 ("ipv6: Create percpu rt6_info")
    Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Cc: Martin KaFai Lau <kafai@xxxxxx>
    Link: https://lore.kernel.org/r/20240604193549.981839-1-edumazet@xxxxxxxxxx
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 8213626434b91..1123594ad2be7 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -962,6 +962,7 @@ static void __fib6_drop_pcpu_from(struct fib6_nh *fib6_nh,
 	if (!fib6_nh->rt6i_pcpu)
 		return;
 
+	rcu_read_lock();
 	/* release the reference to this fib entry from
 	 * all of its cached pcpu routes
 	 */
@@ -970,7 +971,9 @@ static void __fib6_drop_pcpu_from(struct fib6_nh *fib6_nh,
 		struct rt6_info *pcpu_rt;
 
 		ppcpu_rt = per_cpu_ptr(fib6_nh->rt6i_pcpu, cpu);
-		pcpu_rt = *ppcpu_rt;
+
+		/* Paired with xchg() in rt6_get_pcpu_route() */
+		pcpu_rt = READ_ONCE(*ppcpu_rt);
 
 		/* only dropping the 'from' reference if the cached route
 		 * is using 'match'. The cached pcpu_rt->from only changes
@@ -984,6 +987,7 @@ static void __fib6_drop_pcpu_from(struct fib6_nh *fib6_nh,
 			fib6_info_release(from);
 		}
 	}
+	rcu_read_unlock();
 }
 
 struct fib6_nh_pcpu_arg {
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 258e87055836f..627431722f9d6 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1401,6 +1401,7 @@ static struct rt6_info *rt6_get_pcpu_route(const struct fib6_result *res)
 		struct rt6_info *prev, **p;
 
 		p = this_cpu_ptr(res->nh->rt6i_pcpu);
+		/* Paired with READ_ONCE() in __fib6_drop_pcpu_from() */
 		prev = xchg(p, NULL);
 		if (prev) {
 			dst_dev_put(&prev->dst);




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