Re: memory leak in vhost_net_ioctl

[Dmitry Vyukov]

On Thu, Jun 13, 2019 at 4:15 PM Hillf Danton <hdanton@xxxxxxxx> wrote:
>
>
> Hello Dmitry
>
> On Thu, 13 Jun 2019 20:12:06 +0800 Dmitry Vyukov wrote:
> > On Thu, Jun 13, 2019 at 2:07 PM Hillf Danton <hdanton@xxxxxxxx> wrote:
> > >
> > > Hello Jason
> > >
> > > On Thu, 13 Jun 2019 17:10:39 +0800 Jason Wang wrote:
> > > >
> > > > This is basically a kfree(ubuf) after the second vhost_net_flush() in
> > > > vhost_net_release().
> > > >
> > > Fairly good catch.
> > >
> > > > Could you please post a formal patch?
> > > >
> > > I'd like very much to do that; but I wont, I am afraid, until I collect a
> > > Tested-by because of reproducer without a cutting edge.
> >
> > You can easily collect Tested-by from syzbot for any bug with a reproducer;)
> > https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches
> >
> Thank you for the light you are casting.

:)

But you did not ask syzbot to test. That would be something like this
(keeping syzbot email in CC):

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master

(I've attached the patch because my email client is incapable of
sending non-corrupted patches inline, but otherwise inline patches
should work too).


> Here it goes.
> --->8--------
> From: Hillf Danton <hdanton@xxxxxxxx>
> Subject: [PATCH] vhost: fix memory leak in vhost_net_release
>
> syzbot found the following crash on:
>
> HEAD commit:    788a0249 Merge tag 'arc-5.2-rc4' of git://git.kernel.org/p..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x dc9ea6a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?xÃc73825cbdc7326
> dashboard link: https://syzkaller.appspot.com/bug?extid 89f0c7e45efd7bb643
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x b31761a00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x 4892c1a00000
>
>
> udit: type 00 audit(1559768703.229:36): avc:  denied  { map } for
> pidq16 comm="syz-executor330" path="/root/syz-executor330334897"
> dev="sda1" ino 461 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
> tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
> executing program
> executing program
>
> BUG: memory leak
> unreferenced object 0xffff88812421fe40 (size 64):
>    comm "syz-executor330", pid 7117, jiffies 4294949245 (age 13.030s)
>    hex dump (first 32 bytes):
>      01 00 00 00 20 69 6f 63 00 00 00 00 64 65 76 2f  .... ioc....dev/
>      50 fe 21 24 81 88 ff ff 50 fe 21 24 81 88 ff ff  P.!$....P.!$....
>    backtrace:
>      [<00000000ae0c4ae0>] kmemleak_alloc_recursive include/linux/kmemleak.h:55 [inline]
>      [<00000000ae0c4ae0>] slab_post_alloc_hook mm/slab.h:439 [inline]
>      [<00000000ae0c4ae0>] slab_alloc mm/slab.c:3326 [inline]
>      [<00000000ae0c4ae0>] kmem_cache_alloc_trace+0x13d/0x280 mm/slab.c:3553
>      [<0000000079ebab38>] kmalloc include/linux/slab.h:547 [inline]
>      [<0000000079ebab38>] vhost_net_ubuf_alloc drivers/vhost/net.c:241 [inline]
>      [<0000000079ebab38>] vhost_net_set_backend drivers/vhost/net.c:1534 [inline]
>      [<0000000079ebab38>] vhost_net_ioctl+0xb43/0xc10 drivers/vhost/net.c:1716
>      [<000000009f6204a2>] vfs_ioctl fs/ioctl.c:46 [inline]
>      [<000000009f6204a2>] file_ioctl fs/ioctl.c:509 [inline]
>      [<000000009f6204a2>] do_vfs_ioctl+0x62a/0x810 fs/ioctl.c:696
>      [<00000000b45866de>] ksys_ioctl+0x86/0xb0 fs/ioctl.c:713
>      [<00000000dfb41eb8>] __do_sys_ioctl fs/ioctl.c:720 [inline]
>      [<00000000dfb41eb8>] __se_sys_ioctl fs/ioctl.c:718 [inline]
>      [<00000000dfb41eb8>] __x64_sys_ioctl+0x1e/0x30 fs/ioctl.c:718
>      [<0000000049c1f547>] do_syscall_64+0x76/0x1a0 arch/x86/entry/common.c:301
>      [<0000000029cc8ca7>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> BUG: memory leak
> unreferenced object 0xffff88812421fa80 (size 64):
>    comm "syz-executor330", pid 7130, jiffies 4294949755 (age 7.930s)
>    hex dump (first 32 bytes):
>      01 00 00 00 01 00 00 00 00 00 00 00 2f 76 69 72  ............/vir
>      90 fa 21 24 81 88 ff ff 90 fa 21 24 81 88 ff ff  ..!$......!$....
>    backtrace:
>      [<00000000ae0c4ae0>] kmemleak_alloc_recursive  include/linux/kmemleak.h:55 [inline]
>      [<00000000ae0c4ae0>] slab_post_alloc_hook mm/slab.h:439 [inline]
>      [<00000000ae0c4ae0>] slab_alloc mm/slab.c:3326 [inline]
>      [<00000000ae0c4ae0>] kmem_cache_alloc_trace+0x13d/0x280 mm/slab.c:3553
>      [<0000000079ebab38>] kmalloc include/linux/slab.h:547 [inline]
>      [<0000000079ebab38>] vhost_net_ubuf_alloc drivers/vhost/net.c:241  [inline]
>      [<0000000079ebab38>] vhost_net_set_backend drivers/vhost/net.c:1534  [inline]
>      [<0000000079ebab38>] vhost_net_ioctl+0xb43/0xc10  drivers/vhost/net.c:1716
>      [<000000009f6204a2>] vfs_ioctl fs/ioctl.c:46 [inline]
>      [<000000009f6204a2>] file_ioctl fs/ioctl.c:509 [inline]
>      [<000000009f6204a2>] do_vfs_ioctl+0x62a/0x810 fs/ioctl.c:696
>      [<00000000b45866de>] ksys_ioctl+0x86/0xb0 fs/ioctl.c:713
>      [<00000000dfb41eb8>] __do_sys_ioctl fs/ioctl.c:720 [inline]
>      [<00000000dfb41eb8>] __se_sys_ioctl fs/ioctl.c:718 [inline]
>      [<00000000dfb41eb8>] __x64_sys_ioctl+0x1e/0x30 fs/ioctl.c:718
>      [<0000000049c1f547>] do_syscall_64+0x76/0x1a0  arch/x86/entry/common.c:301
>      [<0000000029cc8ca7>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> End of syzbot report.
>
> The function vhost_net_ubuf_alloc() appears in the two cases of dump info, for
> pid 7130 and 7117, suggesting that it is ubuf leak.
>
> Since commit c38e39c378f4 ("vhost-net: fix use-after-free in vhost_net_flush")
> the function vhost_net_flush() had been no longer releasing ubuf.
>
> Freeing the slab after the last flush in the release path fixes it.
>
>
> Fixes: c38e39c378f4 ("vhost-net: fix use-after-free in vhost_net_flush")
> Reported-by: Syzbot <syzbot+0789f0c7e45efd7bb643@xxxxxxxxxxxxxxxxxxxxxxxxx>
> Suggested-by: Jason Wang <jasowang@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Asias He <asias@xxxxxxxxxx>
> Signed-off-by: Hillf Danton <hdanton@xxxxxxxx>
> ---
> This is sent only for collecting Tested-by.
>
>  drivers/vhost/net.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 3beb401..22fae0a 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -1404,6 +1404,7 @@ static int vhost_net_release(struct inode *inode, struct file *f)
>         /* We do an extra flush before freeing memory,
>          * since jobs can re-queue themselves. */
>         vhost_net_flush(n);
> +       kfree(n->vqs[VHOST_NET_VQ_TX].ubufs);
>         kfree(n->vqs[VHOST_NET_VQ_RX].rxq.queue);
>         kfree(n->vqs[VHOST_NET_VQ_TX].xdp);
>         kfree(n->dev.vqs);
> --
>

Attachment: patch
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