On Sat, Oct 7, 2023 at 7:46 PM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote: > > Hi, > > On 9/27/2023 1:32 PM, Hsin-Wei Hung wrote: > > Hi, > > > > We found a potential memory leak in bpf_timer in v5.15.26 using a > > customized syzkaller for fuzzing bpf runtime. It can happen when > > an arraymap is being released. An entry that has been checked by > > bpf_timer_cancel_and_free() can again be initialized by bpf_timer_init(). > > Since both paths are almost identical between v5.15 and net-next, > > I suspect this problem still exists. Below are kmemleak report and > > some additional printks I inserted. > > > > [ 1364.081694] array_map_free_timers map:0xffffc900005a9000 > > [ 1364.081730] ____bpf_timer_init map:0xffffc900005a9000 > > timer:0xffff888001ab4080 > > > > *no bpf_timer_cancel_and_free that will kfree struct bpf_hrtimer* > > at 0xffff888001ab4080 is called > > I think the kmemleak happened as follows: > > bpf_timer_init() > lock timer->lock > read timer->timer as NULL > read map->usercnt != 0 > > bpf_map_put_uref() > // map->usercnt = 0 > atomic_dec_and_test(map->usercnt) > array_map_free_timers() > // just return and lead to mem leak > find timer->timer is NULL > > t = bpf_map_kmalloc_node() > timer->timer = t > unlock timer->lock > > Could you please try the attached patch to check whether the kmemleak > problem has been fixed ? > Hi, Sorry for the late reply to this thread. KASAN is complaining about double-free/invalid-free in the kfree after applying the patch. There are some cases that jump to "out" before the bpf_hrtimer is allocated or when the bpf_hrtimer is already allocated. I am still trying to have a standalone working POC. I think a key to trigger this memory leak is to 1) have a large array map 2) a bpf program init a timer in a small-index entry and then 3) release the map. -Amery > > > > [ 1383.907869] kmemleak: 1 new suspected memory leaks (see > > /sys/kernel/debug/kmemleak) > > BUG: memory leak > > unreferenced object 0xffff888001ab4080 (size 96): > > comm "sshd", pid 279, jiffies 4295233126 (age 29.952s) > > hex dump (first 32 bytes): > > 80 40 ab 01 80 88 ff ff 00 00 00 00 00 00 00 00 .@.............. > > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > > backtrace: > > [<000000009d018da0>] bpf_map_kmalloc_node+0x89/0x1a0 > > [<00000000ebcb33fc>] bpf_timer_init+0x177/0x320 > > [<00000000fb7e90bf>] 0xffffffffc02a0358 > > [<000000000c89ec4f>] __cgroup_bpf_run_filter_skb+0xcbf/0x1110 > > [<00000000fd663fc0>] ip_finish_output+0x13d/0x1f0 > > [<00000000acb3205c>] ip_output+0x19b/0x310 > > [<000000006b584375>] __ip_queue_xmit+0x182e/0x1ed0 > > [<00000000b921b07e>] __tcp_transmit_skb+0x2b65/0x37f0 > > [<0000000026104b23>] tcp_write_xmit+0xf19/0x6290 > > [<000000006dc71bc5>] __tcp_push_pending_frames+0xaf/0x390 > > [<00000000251b364a>] tcp_push+0x452/0x6d0 > > [<000000008522b7d3>] tcp_sendmsg_locked+0x2567/0x3030 > > [<0000000038c644d2>] tcp_sendmsg+0x30/0x50 > > [<000000009fe3413f>] inet_sendmsg+0xba/0x140 > > [<0000000034d78039>] sock_sendmsg+0x13d/0x190 > > [<00000000f55b8db6>] sock_write_iter+0x296/0x3d0 > > > > > > Thanks, > > Hsin-Wei (Amery) > > > > > > . >
