Re: WARNING in bpf_cgroup_link_release

[Dan Carpenter]

On Wed, Apr 15, 2020 at 09:51:40AM -0700, 'Andrii Nakryiko' via syzkaller-bugs wrote:
> On 4/15/20 4:57 AM, Daniel Borkmann wrote:
> > On 4/15/20 8:55 AM, syzbot wrote:
> > > Hello,
> > > 
> > > syzbot found the following crash on:
> > 
> > Andrii, ptal.
> > 
> > > HEAD commit:    1a323ea5 x86: get rid of 'errret' argument to
> > > __get_user_x..
> > > git tree:       bpf-next
> > > console output: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D148ccb57e00000&d=DwICaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=T2Ez0XmyIpHmEa_MPTTUOh61jMDXqwETtTaTbSe-2M4&s=-6XBbsNV1O4X5flrx4Yssfjc56d0qeSHgwHhd92UPJc&e=
> > > kernel config:  https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_.config-3Fx-3D8c1e98458335a7d1&d=DwICaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=T2Ez0XmyIpHmEa_MPTTUOh61jMDXqwETtTaTbSe-2M4&s=s5-1AlWtSiBvo66WN4_UXoXMGIGIqsoUCrmAnxNnfX0&e=
> > > dashboard link: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fextid-3D8a5dadc5c0b1d7055945&d=DwICaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=T2Ez0XmyIpHmEa_MPTTUOh61jMDXqwETtTaTbSe-2M4&s=hAA0702qJH5EwRwvG0RKmj8FwIRm1O8hvmoS7ne5Dls&e=
> > > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > > 
> > > Unfortunately, I don't have any reproducer for this crash yet.
> > > 
> > > IMPORTANT: if you fix the bug, please add the following tag to the
> > > commit:
> > > Reported-by: syzbot+8a5dadc5c0b1d7055945@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > 
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 0 PID: 25081 at kernel/bpf/cgroup.c:796
> > > bpf_cgroup_link_release+0x260/0x3a0 kernel/bpf/cgroup.c:796
> 
> This warning is triggered due to __cgroup_bpf_detach returning an error. It
> can do it only in two cases: either attached item is not found, which from
> starting at code some moreI don't see how that can happen. The other reason
> - kmalloc() failing to allocate memory for new effective prog array.

If you look at the log file then this was allocation fault injection in
bpf_prog_array_alloc().

https://syzkaller.appspot.com/x/log.txt?x=148ccb57e00000

regards,
dan carpenter