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    Subject[PATCH 5.10 06/86] net/sched: cls_u32: fix netns refcount changes in u32_change()
    Date
    From: Eric Dumazet <edumazet@google.com>

    commit 3db09e762dc79584a69c10d74a6b98f89a9979f8 upstream.

    We are now able to detect extra put_net() at the moment
    they happen, instead of much later in correct code paths.

    u32_init_knode() / tcf_exts_init() populates the ->exts.net
    pointer, but as mentioned in tcf_exts_init(),
    the refcount on netns has not been elevated yet.

    The refcount is taken only once tcf_exts_get_net()
    is called.

    So the two u32_destroy_key() calls from u32_change()
    are attempting to release an invalid reference on the netns.

    syzbot report:

    refcount_t: decrement hit 0; leaking memory.
    WARNING: CPU: 0 PID: 21708 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
    Modules linked in:
    CPU: 0 PID: 21708 Comm: syz-executor.5 Not tainted 5.18.0-rc2-next-20220412-syzkaller #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    RIP: 0010:refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
    Code: 1d 14 b6 b2 09 31 ff 89 de e8 6d e9 89 fd 84 db 75 e0 e8 84 e5 89 fd 48 c7 c7 40 aa 26 8a c6 05 f4 b5 b2 09 01 e8 e5 81 2e 05 <0f> 0b eb c4 e8 68 e5 89 fd 0f b6 1d e3 b5 b2 09 31 ff 89 de e8 38
    RSP: 0018:ffffc900051af1b0 EFLAGS: 00010286
    RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
    RDX: 0000000000040000 RSI: ffffffff8160a0c8 RDI: fffff52000a35e28
    RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
    R10: ffffffff81604a9e R11: 0000000000000000 R12: 1ffff92000a35e3b
    R13: 00000000ffffffef R14: ffff8880211a0194 R15: ffff8880577d0a00
    FS: 00007f25d183e700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007f19c859c028 CR3: 0000000051009000 CR4: 00000000003506f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
    <TASK>
    __refcount_dec include/linux/refcount.h:344 [inline]
    refcount_dec include/linux/refcount.h:359 [inline]
    ref_tracker_free+0x535/0x6b0 lib/ref_tracker.c:118
    netns_tracker_free include/net/net_namespace.h:327 [inline]
    put_net_track include/net/net_namespace.h:341 [inline]
    tcf_exts_put_net include/net/pkt_cls.h:255 [inline]
    u32_destroy_key.isra.0+0xa7/0x2b0 net/sched/cls_u32.c:394
    u32_change+0xe01/0x3140 net/sched/cls_u32.c:909
    tc_new_tfilter+0x98d/0x2200 net/sched/cls_api.c:2148
    rtnetlink_rcv_msg+0x80d/0xb80 net/core/rtnetlink.c:6016
    netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2495
    netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
    netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345
    netlink_sendmsg+0x904/0xe00 net/netlink/af_netlink.c:1921
    sock_sendmsg_nosec net/socket.c:705 [inline]
    sock_sendmsg+0xcf/0x120 net/socket.c:725
    ____sys_sendmsg+0x6e2/0x800 net/socket.c:2413
    ___sys_sendmsg+0xf3/0x170 net/socket.c:2467
    __sys_sendmsg+0xe5/0x1b0 net/socket.c:2496
    do_syscall_x64 arch/x86/entry/common.c:50 [inline]
    do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
    entry_SYSCALL_64_after_hwframe+0x44/0xae
    RIP: 0033:0x7f25d0689049
    Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
    RSP: 002b:00007f25d183e168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
    RAX: ffffffffffffffda RBX: 00007f25d079c030 RCX: 00007f25d0689049
    RDX: 0000000000000000 RSI: 0000000020000340 RDI: 0000000000000005
    RBP: 00007f25d06e308d R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
    R13: 00007ffd0b752e3f R14: 00007f25d183e300 R15: 0000000000022000
    </TASK>

    Fixes: 35c55fc156d8 ("cls_u32: use tcf_exts_get_net() before call_rcu()")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Cc: Cong Wang <xiyou.wangcong@gmail.com>
    Cc: Jiri Pirko <jiri@resnulli.us>
    Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/sched/cls_u32.c | 16 ++++++++++------
    1 file changed, 10 insertions(+), 6 deletions(-)

    --- a/net/sched/cls_u32.c
    +++ b/net/sched/cls_u32.c
    @@ -386,14 +386,19 @@ static int u32_init(struct tcf_proto *tp
    return 0;
    }

    -static int u32_destroy_key(struct tc_u_knode *n, bool free_pf)
    +static void __u32_destroy_key(struct tc_u_knode *n)
    {
    struct tc_u_hnode *ht = rtnl_dereference(n->ht_down);

    tcf_exts_destroy(&n->exts);
    - tcf_exts_put_net(&n->exts);
    if (ht && --ht->refcnt == 0)
    kfree(ht);
    + kfree(n);
    +}
    +
    +static void u32_destroy_key(struct tc_u_knode *n, bool free_pf)
    +{
    + tcf_exts_put_net(&n->exts);
    #ifdef CONFIG_CLS_U32_PERF
    if (free_pf)
    free_percpu(n->pf);
    @@ -402,8 +407,7 @@ static int u32_destroy_key(struct tc_u_k
    if (free_pf)
    free_percpu(n->pcpu_success);
    #endif
    - kfree(n);
    - return 0;
    + __u32_destroy_key(n);
    }

    /* u32_delete_key_rcu should be called when free'ing a copied
    @@ -898,13 +902,13 @@ static int u32_change(struct net *net, s
    tca[TCA_RATE], ovr, extack);

    if (err) {
    - u32_destroy_key(new, false);
    + __u32_destroy_key(new);
    return err;
    }

    err = u32_replace_hw_knode(tp, new, flags, extack);
    if (err) {
    - u32_destroy_key(new, false);
    + __u32_destroy_key(new);
    return err;
    }


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