Patch "udp: Set SOCK_RCU_FREE earlier in udp_lib_get_port()." 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

    udp: Set SOCK_RCU_FREE earlier in udp_lib_get_port().

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:
     udp-set-sock_rcu_free-earlier-in-udp_lib_get_port.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 139f02dcb0bb8d37a5229c7a8b5c2b206eb18227
Author: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Date:   Tue Jul 9 12:13:56 2024 -0700

    udp: Set SOCK_RCU_FREE earlier in udp_lib_get_port().
    
    [ Upstream commit 5c0b485a8c6116516f33925b9ce5b6104a6eadfd ]
    
    syzkaller triggered the warning [0] in udp_v4_early_demux().
    
    In udp_v[46]_early_demux() and sk_lookup(), we do not touch the refcount
    of the looked-up sk and use sock_pfree() as skb->destructor, so we check
    SOCK_RCU_FREE to ensure that the sk is safe to access during the RCU grace
    period.
    
    Currently, SOCK_RCU_FREE is flagged for a bound socket after being put
    into the hash table.  Moreover, the SOCK_RCU_FREE check is done too early
    in udp_v[46]_early_demux() and sk_lookup(), so there could be a small race
    window:
    
      CPU1                                 CPU2
      ----                                 ----
      udp_v4_early_demux()                 udp_lib_get_port()
      |                                    |- hlist_add_head_rcu()
      |- sk = __udp4_lib_demux_lookup()    |
      |- DEBUG_NET_WARN_ON_ONCE(sk_is_refcounted(sk));
                                           `- sock_set_flag(sk, SOCK_RCU_FREE)
    
    We had the same bug in TCP and fixed it in commit 871019b22d1b ("net:
    set SOCK_RCU_FREE before inserting socket into hashtable").
    
    Let's apply the same fix for UDP.
    
    [0]:
    WARNING: CPU: 0 PID: 11198 at net/ipv4/udp.c:2599 udp_v4_early_demux+0x481/0xb70 net/ipv4/udp.c:2599
    Modules linked in:
    CPU: 0 PID: 11198 Comm: syz-executor.1 Not tainted 6.9.0-g93bda33046e7 #13
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
    RIP: 0010:udp_v4_early_demux+0x481/0xb70 net/ipv4/udp.c:2599
    Code: c5 7a 15 fe bb 01 00 00 00 44 89 e9 31 ff d3 e3 81 e3 bf ef ff ff 89 de e8 2c 74 15 fe 85 db 0f 85 02 06 00 00 e8 9f 7a 15 fe <0f> 0b e8 98 7a 15 fe 49 8d 7e 60 e8 4f 39 2f fe 49 c7 46 60 20 52
    RSP: 0018:ffffc9000ce3fa58 EFLAGS: 00010293
    RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff8318c92c
    RDX: ffff888036ccde00 RSI: ffffffff8318c2f1 RDI: 0000000000000001
    RBP: ffff88805a2dd6e0 R08: 0000000000000001 R09: 0000000000000000
    R10: 0000000000000000 R11: 0001ffffffffffff R12: ffff88805a2dd680
    R13: 0000000000000007 R14: ffff88800923f900 R15: ffff88805456004e
    FS:  00007fc449127640(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007fc449126e38 CR3: 000000003de4b002 CR4: 0000000000770ef0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
    PKRU: 55555554
    Call Trace:
     <TASK>
     ip_rcv_finish_core.constprop.0+0xbdd/0xd20 net/ipv4/ip_input.c:349
     ip_rcv_finish+0xda/0x150 net/ipv4/ip_input.c:447
     NF_HOOK include/linux/netfilter.h:314 [inline]
     NF_HOOK include/linux/netfilter.h:308 [inline]
     ip_rcv+0x16c/0x180 net/ipv4/ip_input.c:569
     __netif_receive_skb_one_core+0xb3/0xe0 net/core/dev.c:5624
     __netif_receive_skb+0x21/0xd0 net/core/dev.c:5738
     netif_receive_skb_internal net/core/dev.c:5824 [inline]
     netif_receive_skb+0x271/0x300 net/core/dev.c:5884
     tun_rx_batched drivers/net/tun.c:1549 [inline]
     tun_get_user+0x24db/0x2c50 drivers/net/tun.c:2002
     tun_chr_write_iter+0x107/0x1a0 drivers/net/tun.c:2048
     new_sync_write fs/read_write.c:497 [inline]
     vfs_write+0x76f/0x8d0 fs/read_write.c:590
     ksys_write+0xbf/0x190 fs/read_write.c:643
     __do_sys_write fs/read_write.c:655 [inline]
     __se_sys_write fs/read_write.c:652 [inline]
     __x64_sys_write+0x41/0x50 fs/read_write.c:652
     x64_sys_call+0xe66/0x1990 arch/x86/include/generated/asm/syscalls_64.h:2
     do_syscall_x64 arch/x86/entry/common.c:52 [inline]
     do_syscall_64+0x4b/0x110 arch/x86/entry/common.c:83
     entry_SYSCALL_64_after_hwframe+0x4b/0x53
    RIP: 0033:0x7fc44a68bc1f
    Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 e9 cf f5 ff 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 3c d0 f5 ff 48
    RSP: 002b:00007fc449126c90 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
    RAX: ffffffffffffffda RBX: 00000000004bc050 RCX: 00007fc44a68bc1f
    RDX: 0000000000000032 RSI: 00000000200000c0 RDI: 00000000000000c8
    RBP: 00000000004bc050 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000032 R11: 0000000000000293 R12: 0000000000000000
    R13: 000000000000000b R14: 00007fc44a5ec530 R15: 0000000000000000
     </TASK>
    
    Fixes: 6acc9b432e67 ("bpf: Add helper to retrieve socket in BPF")
    Reported-by: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
    Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
    Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Link: https://patch.msgid.link/20240709191356.24010-1-kuniyu@xxxxxxxxxx
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index b8f93c1479ae1..53267566808c1 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -319,6 +319,8 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
 			goto fail_unlock;
 		}
 
+		sock_set_flag(sk, SOCK_RCU_FREE);
+
 		sk_add_node_rcu(sk, &hslot->head);
 		hslot->count++;
 		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
@@ -335,7 +337,7 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
 		hslot2->count++;
 		spin_unlock(&hslot2->lock);
 	}
-	sock_set_flag(sk, SOCK_RCU_FREE);
+
 	error = 0;
 fail_unlock:
 	spin_unlock_bh(&hslot->lock);




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