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    Subject[PATCH AUTOSEL 4.19 9/9] l2tp: do not use inet_hash()/inet_unhash()
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 02c71b144c811bcdd865e0a1226d0407d11357e8 ]

    syzbot recently found a way to crash the kernel [1]

    Issue here is that inet_hash() & inet_unhash() are currently
    only meant to be used by TCP & DCCP, since only these protocols
    provide the needed hashinfo pointer.

    L2TP uses a single list (instead of a hash table)

    This old bug became an issue after commit 610236587600
    ("bpf: Add new cgroup attach type to enable sock modifications")
    since after this commit, sk_common_release() can be called
    while the L2TP socket is still considered 'hashed'.

    general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
    KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
    CPU: 0 PID: 7063 Comm: syz-executor654 Not tainted 5.7.0-rc6-syzkaller #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    RIP: 0010:inet_unhash+0x11f/0x770 net/ipv4/inet_hashtables.c:600
    Code: 03 0f b6 04 02 84 c0 74 08 3c 03 0f 8e dd 04 00 00 48 8d 7d 08 44 8b 73 08 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 55 05 00 00 48 8d 7d 14 4c 8b 6d 08 48 b8 00 00
    RSP: 0018:ffffc90001777d30 EFLAGS: 00010202
    RAX: dffffc0000000000 RBX: ffff88809a6df940 RCX: ffffffff8697c242
    RDX: 0000000000000001 RSI: ffffffff8697c251 RDI: 0000000000000008
    RBP: 0000000000000000 R08: ffff88809f3ae1c0 R09: fffffbfff1514cc1
    R10: ffffffff8a8a6607 R11: fffffbfff1514cc0 R12: ffff88809a6df9b0
    R13: 0000000000000007 R14: 0000000000000000 R15: ffffffff873a4d00
    FS: 0000000001d2b880(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00000000006cd090 CR3: 000000009403a000 CR4: 00000000001406f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
    sk_common_release+0xba/0x370 net/core/sock.c:3210
    inet_create net/ipv4/af_inet.c:390 [inline]
    inet_create+0x966/0xe00 net/ipv4/af_inet.c:248
    __sock_create+0x3cb/0x730 net/socket.c:1428
    sock_create net/socket.c:1479 [inline]
    __sys_socket+0xef/0x200 net/socket.c:1521
    __do_sys_socket net/socket.c:1530 [inline]
    __se_sys_socket net/socket.c:1528 [inline]
    __x64_sys_socket+0x6f/0xb0 net/socket.c:1528
    do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
    entry_SYSCALL_64_after_hwframe+0x49/0xb3
    RIP: 0033:0x441e29
    Code: e8 fc b3 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 eb 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
    RSP: 002b:00007ffdce184148 EFLAGS: 00000246 ORIG_RAX: 0000000000000029
    RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000441e29
    RDX: 0000000000000073 RSI: 0000000000000002 RDI: 0000000000000002
    RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
    R13: 0000000000402c30 R14: 0000000000000000 R15: 0000000000000000
    Modules linked in:
    ---[ end trace 23b6578228ce553e ]---
    RIP: 0010:inet_unhash+0x11f/0x770 net/ipv4/inet_hashtables.c:600
    Code: 03 0f b6 04 02 84 c0 74 08 3c 03 0f 8e dd 04 00 00 48 8d 7d 08 44 8b 73 08 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 55 05 00 00 48 8d 7d 14 4c 8b 6d 08 48 b8 00 00
    RSP: 0018:ffffc90001777d30 EFLAGS: 00010202
    RAX: dffffc0000000000 RBX: ffff88809a6df940 RCX: ffffffff8697c242
    RDX: 0000000000000001 RSI: ffffffff8697c251 RDI: 0000000000000008
    RBP: 0000000000000000 R08: ffff88809f3ae1c0 R09: fffffbfff1514cc1
    R10: ffffffff8a8a6607 R11: fffffbfff1514cc0 R12: ffff88809a6df9b0
    R13: 0000000000000007 R14: 0000000000000000 R15: ffffffff873a4d00
    FS: 0000000001d2b880(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00000000006cd090 CR3: 000000009403a000 CR4: 00000000001406f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

    Fixes: 0d76751fad77 ("l2tp: Add L2TPv3 IP encapsulation (no UDP) support")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Cc: James Chapman <jchapman@katalix.com>
    Cc: Andrii Nakryiko <andriin@fb.com>
    Reported-by: syzbot+3610d489778b57cc8031@syzkaller.appspotmail.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/l2tp/l2tp_ip.c | 29 ++++++++++++++++++++++-------
    net/l2tp/l2tp_ip6.c | 30 ++++++++++++++++++++++--------
    2 files changed, 44 insertions(+), 15 deletions(-)

    diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
    index d4c60523c549..99881b81f302 100644
    --- a/net/l2tp/l2tp_ip.c
    +++ b/net/l2tp/l2tp_ip.c
    @@ -24,7 +24,6 @@
    #include <net/icmp.h>
    #include <net/udp.h>
    #include <net/inet_common.h>
    -#include <net/inet_hashtables.h>
    #include <net/tcp_states.h>
    #include <net/protocol.h>
    #include <net/xfrm.h>
    @@ -213,15 +212,31 @@ static int l2tp_ip_recv(struct sk_buff *skb)
    return 0;
    }

    -static int l2tp_ip_open(struct sock *sk)
    +static int l2tp_ip_hash(struct sock *sk)
    {
    - /* Prevent autobind. We don't have ports. */
    - inet_sk(sk)->inet_num = IPPROTO_L2TP;
    + if (sk_unhashed(sk)) {
    + write_lock_bh(&l2tp_ip_lock);
    + sk_add_node(sk, &l2tp_ip_table);
    + write_unlock_bh(&l2tp_ip_lock);
    + }
    + return 0;
    +}

    +static void l2tp_ip_unhash(struct sock *sk)
    +{
    + if (sk_unhashed(sk))
    + return;
    write_lock_bh(&l2tp_ip_lock);
    - sk_add_node(sk, &l2tp_ip_table);
    + sk_del_node_init(sk);
    write_unlock_bh(&l2tp_ip_lock);
    +}
    +
    +static int l2tp_ip_open(struct sock *sk)
    +{
    + /* Prevent autobind. We don't have ports. */
    + inet_sk(sk)->inet_num = IPPROTO_L2TP;

    + l2tp_ip_hash(sk);
    return 0;
    }

    @@ -598,8 +613,8 @@ static struct proto l2tp_ip_prot = {
    .sendmsg = l2tp_ip_sendmsg,
    .recvmsg = l2tp_ip_recvmsg,
    .backlog_rcv = l2tp_ip_backlog_recv,
    - .hash = inet_hash,
    - .unhash = inet_unhash,
    + .hash = l2tp_ip_hash,
    + .unhash = l2tp_ip_unhash,
    .obj_size = sizeof(struct l2tp_ip_sock),
    #ifdef CONFIG_COMPAT
    .compat_setsockopt = compat_ip_setsockopt,
    diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
    index 2f28f9910b92..2ff25c445b82 100644
    --- a/net/l2tp/l2tp_ip6.c
    +++ b/net/l2tp/l2tp_ip6.c
    @@ -24,8 +24,6 @@
    #include <net/icmp.h>
    #include <net/udp.h>
    #include <net/inet_common.h>
    -#include <net/inet_hashtables.h>
    -#include <net/inet6_hashtables.h>
    #include <net/tcp_states.h>
    #include <net/protocol.h>
    #include <net/xfrm.h>
    @@ -226,15 +224,31 @@ static int l2tp_ip6_recv(struct sk_buff *skb)
    return 0;
    }

    -static int l2tp_ip6_open(struct sock *sk)
    +static int l2tp_ip6_hash(struct sock *sk)
    {
    - /* Prevent autobind. We don't have ports. */
    - inet_sk(sk)->inet_num = IPPROTO_L2TP;
    + if (sk_unhashed(sk)) {
    + write_lock_bh(&l2tp_ip6_lock);
    + sk_add_node(sk, &l2tp_ip6_table);
    + write_unlock_bh(&l2tp_ip6_lock);
    + }
    + return 0;
    +}

    +static void l2tp_ip6_unhash(struct sock *sk)
    +{
    + if (sk_unhashed(sk))
    + return;
    write_lock_bh(&l2tp_ip6_lock);
    - sk_add_node(sk, &l2tp_ip6_table);
    + sk_del_node_init(sk);
    write_unlock_bh(&l2tp_ip6_lock);
    +}
    +
    +static int l2tp_ip6_open(struct sock *sk)
    +{
    + /* Prevent autobind. We don't have ports. */
    + inet_sk(sk)->inet_num = IPPROTO_L2TP;

    + l2tp_ip6_hash(sk);
    return 0;
    }

    @@ -732,8 +746,8 @@ static struct proto l2tp_ip6_prot = {
    .sendmsg = l2tp_ip6_sendmsg,
    .recvmsg = l2tp_ip6_recvmsg,
    .backlog_rcv = l2tp_ip6_backlog_recv,
    - .hash = inet6_hash,
    - .unhash = inet_unhash,
    + .hash = l2tp_ip6_hash,
    + .unhash = l2tp_ip6_unhash,
    .obj_size = sizeof(struct l2tp_ip6_sock),
    #ifdef CONFIG_COMPAT
    .compat_setsockopt = compat_ipv6_setsockopt,
    --
    2.25.1
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