Re: [PATCH] ieee802154: hwsim: fix memory leak in __pskb_copy_fclone

[Dongliang Mu <mudongliangabcd@gmail.com>]

On Tue, Jul 13, 2021 at 9:47 PM Alexander Aring <alex.aring@gmail.com> wrote:
>
> Hi,
>
> On Tue, 13 Jul 2021 at 01:40, Dongliang Mu <mudongliangabcd@gmail.com> wrote:
> >
> > hwsim_hw_xmit fails to deallocate the newskb copied by pskb_copy. Fix
> > this by adding kfree_skb after ieee802154_rx_irqsafe.
> >
> >   [<ffffffff836433fb>] __alloc_skb+0x22b/0x250 net/core/skbuff.c:414
> >   [<ffffffff8364ad95>] __pskb_copy_fclone+0x75/0x360 net/core/skbuff.c:1609
> >   [<ffffffff82ae65e3>] __pskb_copy include/linux/skbuff.h:1176 [inline]
> >   [<ffffffff82ae65e3>] pskb_copy include/linux/skbuff.h:3207 [inline]
> >   [<ffffffff82ae65e3>] hwsim_hw_xmit+0xd3/0x140 drivers/net/ieee802154/mac802154_hwsim.c:132
> >   [<ffffffff83ff8f47>] drv_xmit_async net/mac802154/driver-ops.h:16 [inline]
> >   [<ffffffff83ff8f47>] ieee802154_tx+0xc7/0x190 net/mac802154/tx.c:83
> >   [<ffffffff83ff9138>] ieee802154_subif_start_xmit+0x58/0x70 net/mac802154/tx.c:132
> >   [<ffffffff83670b82>] __netdev_start_xmit include/linux/netdevice.h:4944 [inline]
> >   [<ffffffff83670b82>] netdev_start_xmit include/linux/netdevice.h:4958 [inline]
> >   [<ffffffff83670b82>] xmit_one net/core/dev.c:3658 [inline]
> >   [<ffffffff83670b82>] dev_hard_start_xmit+0xe2/0x330 net/core/dev.c:3674
> >   [<ffffffff83718028>] sch_direct_xmit+0xf8/0x520 net/sched/sch_generic.c:342
> >   [<ffffffff8367193b>] __dev_xmit_skb net/core/dev.c:3874 [inline]
> >   [<ffffffff8367193b>] __dev_queue_xmit+0xa3b/0x1360 net/core/dev.c:4241
> >   [<ffffffff83ff5437>] dgram_sendmsg+0x437/0x570 net/ieee802154/socket.c:682
> >   [<ffffffff836345b6>] sock_sendmsg_nosec net/socket.c:702 [inline]
> >   [<ffffffff836345b6>] sock_sendmsg+0x56/0x80 net/socket.c:722
> >
> > Fixes: f25da51fdc38 ("ieee802154: hwsim: add replacement for fakelb")
> > Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
>
> sorry, I don't get the fix. Is this a memory leak? I remember there
> was something reported by syzkaller [0] but I wasn't able yet to get
> into it. Is it what you referring to?

Yes, you're right.

I get this memory leak many times in my local syzkaller instance but
do not recognize there is already a bug report in the syzbot
dashboard.

> __pskb_copy_fclone() shows "The returned buffer has a reference count
> of 1" and ieee802154_rx_irqsafe() will queue the skb for a tasklet.
> With your patch it will be immediately freed and a use after free will
> occur.

Thanks for your feedback. I am sorry about this fix since I did not
observe UAF in my testing.

I will keep learning more materials about socket in Linux kernel. :)

> I believe there is something wrong in the error path of
> 802.15.4 frame parsing and that's why we sometimes have a leaks there.

Should be yes, it occurs many times in my local syzkaller instance.

>
> I need to test this patch, but I don't get how this patch is supposed
> to fix the issue.

This patch should be incorrect. Please directly focus on bug reports
on the syzbot dashboard. If possible, please cc me your final patch
about this bug. I can learn something from this bug.

Best regards
Dongliang Mu

>
> - Alex
>
> [0] https://groups.google.com/g/syzkaller-bugs/c/EoIvZbk3Zfo/m/AlKUiErlAwAJ