Re: [PATCH net v2] net: bridge: fix memleak in br_add_if()

[Nikolay Aleksandrov]

On 09/08/2021 12:02, Yang Yingliang wrote:
> I got a memleak report:
> 
> BUG: memory leak
> unreferenced object 0x607ee521a658 (size 240):
> comm "syz-executor.0", pid 955, jiffies 4294780569 (age 16.449s)
> hex dump (first 32 bytes, cpu 1):
> 00 00 00 00 00 00 00 00 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:
> [<00000000d830ea5a>] br_multicast_add_port+0x1c2/0x300 net/bridge/br_multicast.c:1693
> [<00000000274d9a71>] new_nbp net/bridge/br_if.c:435 [inline]
> [<00000000274d9a71>] br_add_if+0x670/0x1740 net/bridge/br_if.c:611
> [<0000000012ce888e>] do_set_master net/core/rtnetlink.c:2513 [inline]
> [<0000000012ce888e>] do_set_master+0x1aa/0x210 net/core/rtnetlink.c:2487
> [<0000000099d1cafc>] __rtnl_newlink+0x1095/0x13e0 net/core/rtnetlink.c:3457
> [<00000000a01facc0>] rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3488
> [<00000000acc9186c>] rtnetlink_rcv_msg+0x369/0xa10 net/core/rtnetlink.c:5550
> [<00000000d4aabb9c>] netlink_rcv_skb+0x134/0x3d0 net/netlink/af_netlink.c:2504
> [<00000000bc2e12a3>] netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
> [<00000000bc2e12a3>] netlink_unicast+0x4a0/0x6a0 net/netlink/af_netlink.c:1340
> [<00000000e4dc2d0e>] netlink_sendmsg+0x789/0xc70 net/netlink/af_netlink.c:1929
> [<000000000d22c8b3>] sock_sendmsg_nosec net/socket.c:654 [inline]
> [<000000000d22c8b3>] sock_sendmsg+0x139/0x170 net/socket.c:674
> [<00000000e281417a>] ____sys_sendmsg+0x658/0x7d0 net/socket.c:2350
> [<00000000237aa2ab>] ___sys_sendmsg+0xf8/0x170 net/socket.c:2404
> [<000000004f2dc381>] __sys_sendmsg+0xd3/0x190 net/socket.c:2433
> [<0000000005feca6c>] do_syscall_64+0x37/0x90 arch/x86/entry/common.c:47
> [<000000007304477d>] entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> On error path of br_add_if(), p->mcast_stats allocated in
> new_nbp() need be freed, or it will be leaked.
> 
> Fixes: 1080ab95e3c7 ("net: bridge: add support for IGMP/MLD stats and export them via netlink")
> Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
> Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> ---
> v2:
>   move free_percpu(p->mcast_stats) in release_nbp() and
>   fix the compile error when CONFIG_BRIDGE_IGMP_SNOOPING
>   is disabled.
> ---
>  net/bridge/br_if.c        | 5 ++++-
>  net/bridge/br_multicast.c | 1 -
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 

You can add a helper to free mcast stats and use it in the error path.
I'd like to keep the port dismantling code as it's currently done, moving
multicast stats freeing away from br_multicast_del_port is wrong.

In fact I think you can directly use br_multicast_del_port() as it's a noop w.r.t the
other actions (stopping timers that were never started and walking empty lists).
You'll have to test it, of course.

For this patch:
Nacked-by: Nikolay Aleksandrov <nikolay@xxxxxxxxxx>

Thanks,
 Nik