On Tue, Sep 5, 2017 at 8:47 PM, Xin Long <lucien....@gmail.com> wrote: > ChunYu found a netlink use-after-free issue by syzkaller: > > [28448.842981] BUG: KASAN: use-after-free in __nla_put+0x37/0x40 at addr > ffff8807185e2378 > [28448.969918] Call Trace: > [...] > [28449.117207] __nla_put+0x37/0x40 > [28449.132027] nla_put+0xf5/0x130 > [28449.146261] sk_diag_fill.isra.4.constprop.5+0x5a0/0x750 [netlink_diag] > [28449.176608] __netlink_diag_dump+0x25a/0x700 [netlink_diag] > [28449.202215] netlink_diag_dump+0x176/0x240 [netlink_diag] > [28449.226834] netlink_dump+0x488/0xbb0 > [28449.298014] __netlink_dump_start+0x4e8/0x760 > [28449.317924] netlink_diag_handler_dump+0x261/0x340 [netlink_diag] > [28449.413414] sock_diag_rcv_msg+0x207/0x390 > [28449.432409] netlink_rcv_skb+0x149/0x380 > [28449.467647] sock_diag_rcv+0x2d/0x40 > [28449.484362] netlink_unicast+0x562/0x7b0 > [28449.564790] netlink_sendmsg+0xaa8/0xe60 > [28449.661510] sock_sendmsg+0xcf/0x110 > [28449.865631] __sys_sendmsg+0xf3/0x240 > [28450.000964] SyS_sendmsg+0x32/0x50 > [28450.016969] do_syscall_64+0x25c/0x6c0 > [28450.154439] entry_SYSCALL64_slow_path+0x25/0x25 > > It was caused by no protection between nlk groups' free in netlink_release > and nlk groups' accessing in sk_diag_dump_groups. The similar issue also > exists in netlink_seq_show(). > > This patch is to defer nlk groups' free in deferred_put_nlk_sk.
This looks odd too, at least not complete. The netlink sock itself is protected by RCU to speed up the lookup path, but not necessarily nlk->groups, at least I don't see rcu_dereference() in sk_diag_dump_groups(). And netlink_realloc_groups() needs fix too, right? Otherwise krealloc() could reallocate a brand new memory and existing readers will crash too? I am afraid you need more work to make nlk->groups RCU friendly. RCU is not just about call_rcu(), both readers and writers need to use proper RCU API.
