The problem happens when I add seccomp filter to whiltelist syscall "ioctl" with arguments of type 'U', for SNDRV_CTL_IOCTL_TLV_READ, SNDRV_CTL_IOCTL_TLV_WRITE and SNDRV_CTL_IOCTL_TLV_COMMAND. I was expecting snd_ctl_hw_elem_tlv() to run without problem, but actually seeing it return error because of ioctl() call failure. In control_hw.c, when the local int "inum" got passed to ioctl, it is converted to "unsigned long". Take SNDRV_CTL_IOCTL_TLV_WRITE as example, it will stretch to 0xffffffffc008551b. This doesn't bring problem to snd function, I think it's because snd_pcm_lib_ioctl takes "unsigned int cmd" as argument. https://github.com/torvalds/linux/blob/master/sound/core/pcm_lib.c#L1769 However the seccomp_data struct takes 64 bits argument to check against seccomp rules. https://github.com/torvalds/linux/blob/master/arch/x86/entry/common.c#L104 and these unexpected 0xff bytes make the seccomp rule check fail. Since ioctl takes "unsigned long" command, I think we should fix this in alsa-lib as there is no intention to append the 0xff bytes to kernel. Thanks, Hsin-yu On Wed, Aug 15, 2018 at 5:37 PM Takashi Iwai <tiwai@xxxxxxx> wrote: > > On Wed, 15 Aug 2018 10:17:50 +0200, > Hsin-Yu Chao wrote: > > > > When seccomp policy is applied to filter ioctl syscall with > > SNDRV_CTL_IOCTL_TLV_COMMAND, SNDRV_CTL_IOCTL_TLV_READ and > > SNDRV_CTL_IOCTL_TLV_WRITE in whiltelist, alsa-lib still breaks > > in at snd_ctl_hw_elem_tlv(). > > Fix the problem by passing unsigned int to ioctl. > > Could you explain exactly what breaks and how? > > > thanks, > > Takashi > > > > > Signed-off-by: Hsin-Yu Chao <hychao@xxxxxxxxxxxx> > > --- > > src/control/control_hw.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/src/control/control_hw.c b/src/control/control_hw.c > > index 68eca522..b54d65f2 100644 > > --- a/src/control/control_hw.c > > +++ b/src/control/control_hw.c > > @@ -215,7 +215,7 @@ static int snd_ctl_hw_elem_tlv(snd_ctl_t *handle, int op_flag, > > unsigned int numid, > > unsigned int *tlv, unsigned int tlv_size) > > { > > - int inum; > > + unsigned int inum; > > snd_ctl_hw_t *hw = handle->private_data; > > struct snd_ctl_tlv *xtlv; > > > > -- > > 2.18.0.865.gffc8e1a3cd6-goog > > > > _______________________________________________ > > Alsa-devel mailing list > > Alsa-devel@xxxxxxxxxxxxxxxx > > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel > > _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
