Patch "netns: Make get_net_ns() handle zero refcount net" has been added to the 5.15-stable tree

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

    netns: Make get_net_ns() handle zero refcount net

to the 5.15-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:
     netns-make-get_net_ns-handle-zero-refcount-net.patch
and it can be found in the queue-5.15 subdirectory.

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



commit ab301d9cbc060b9b84a8cad87c2d39da42055b36
Author: Yue Haibing <yuehaibing@xxxxxxxxxx>
Date:   Fri Jun 14 21:13:02 2024 +0800

    netns: Make get_net_ns() handle zero refcount net
    
    [ Upstream commit ff960f9d3edbe08a736b5a224d91a305ccc946b0 ]
    
    Syzkaller hit a warning:
    refcount_t: addition on 0; use-after-free.
    WARNING: CPU: 3 PID: 7890 at lib/refcount.c:25 refcount_warn_saturate+0xdf/0x1d0
    Modules linked in:
    CPU: 3 PID: 7890 Comm: tun Not tainted 6.10.0-rc3-00100-gcaa4f9578aba-dirty #310
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
    RIP: 0010:refcount_warn_saturate+0xdf/0x1d0
    Code: 41 49 04 31 ff 89 de e8 9f 1e cd fe 84 db 75 9c e8 76 26 cd fe c6 05 b6 41 49 04 01 90 48 c7 c7 b8 8e 25 86 e8 d2 05 b5 fe 90 <0f> 0b 90 90 e9 79 ff ff ff e8 53 26 cd fe 0f b6 1
    RSP: 0018:ffff8881067b7da0 EFLAGS: 00010286
    RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff811c72ac
    RDX: ffff8881026a2140 RSI: ffffffff811c72b5 RDI: 0000000000000001
    RBP: ffff8881067b7db0 R08: 0000000000000000 R09: 205b5d3730353139
    R10: 0000000000000000 R11: 205d303938375420 R12: ffff8881086500c4
    R13: ffff8881086500c4 R14: ffff8881086500b0 R15: ffff888108650040
    FS:  00007f5b2961a4c0(0000) GS:ffff88823bd00000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 000055d7ed36fd18 CR3: 00000001482f6000 CR4: 00000000000006f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
     <TASK>
     ? show_regs+0xa3/0xc0
     ? __warn+0xa5/0x1c0
     ? refcount_warn_saturate+0xdf/0x1d0
     ? report_bug+0x1fc/0x2d0
     ? refcount_warn_saturate+0xdf/0x1d0
     ? handle_bug+0xa1/0x110
     ? exc_invalid_op+0x3c/0xb0
     ? asm_exc_invalid_op+0x1f/0x30
     ? __warn_printk+0xcc/0x140
     ? __warn_printk+0xd5/0x140
     ? refcount_warn_saturate+0xdf/0x1d0
     get_net_ns+0xa4/0xc0
     ? __pfx_get_net_ns+0x10/0x10
     open_related_ns+0x5a/0x130
     __tun_chr_ioctl+0x1616/0x2370
     ? __sanitizer_cov_trace_switch+0x58/0xa0
     ? __sanitizer_cov_trace_const_cmp2+0x1c/0x30
     ? __pfx_tun_chr_ioctl+0x10/0x10
     tun_chr_ioctl+0x2f/0x40
     __x64_sys_ioctl+0x11b/0x160
     x64_sys_call+0x1211/0x20d0
     do_syscall_64+0x9e/0x1d0
     entry_SYSCALL_64_after_hwframe+0x77/0x7f
    RIP: 0033:0x7f5b28f165d7
    Code: b3 66 90 48 8b 05 b1 48 2d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 81 48 2d 00 8
    RSP: 002b:00007ffc2b59c5e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
    RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5b28f165d7
    RDX: 0000000000000000 RSI: 00000000000054e3 RDI: 0000000000000003
    RBP: 00007ffc2b59c650 R08: 00007f5b291ed8c0 R09: 00007f5b2961a4c0
    R10: 0000000029690010 R11: 0000000000000246 R12: 0000000000400730
    R13: 00007ffc2b59cf40 R14: 0000000000000000 R15: 0000000000000000
     </TASK>
    Kernel panic - not syncing: kernel: panic_on_warn set ...
    
    This is trigger as below:
              ns0                                    ns1
    tun_set_iff() //dev is tun0
       tun->dev = dev
    //ip link set tun0 netns ns1
                                           put_net() //ref is 0
    __tun_chr_ioctl() //TUNGETDEVNETNS
       net = dev_net(tun->dev);
       open_related_ns(&net->ns, get_net_ns); //ns1
         get_net_ns()
            get_net() //addition on 0
    
    Use maybe_get_net() in get_net_ns in case net's ref is zero to fix this
    
    Fixes: 0c3e0e3bb623 ("tun: Add ioctl() TUNGETDEVNETNS cmd to allow obtaining real net ns of tun device")
    Signed-off-by: Yue Haibing <yuehaibing@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240614131302.2698509-1-yuehaibing@xxxxxxxxxx
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index a209db33fa5f7..3addbce20f8ed 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -651,11 +651,16 @@ EXPORT_SYMBOL_GPL(__put_net);
  * get_net_ns - increment the refcount of the network namespace
  * @ns: common namespace (net)
  *
- * Returns the net's common namespace.
+ * Returns the net's common namespace or ERR_PTR() if ref is zero.
  */
 struct ns_common *get_net_ns(struct ns_common *ns)
 {
-	return &get_net(container_of(ns, struct net, ns))->ns;
+	struct net *net;
+
+	net = maybe_get_net(container_of(ns, struct net, ns));
+	if (net)
+		return &net->ns;
+	return ERR_PTR(-EINVAL);
 }
 EXPORT_SYMBOL_GPL(get_net_ns);
 




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