On Fri, Oct 08, 2021 at 11:24:39AM +0200, Arnd Bergmann wrote:
On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai tiwai@suse.de wrote:
On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote:
On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
@@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr { #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN) typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)]; typedef char __pad_after_uframe[0]; +typedef char __pad_before_u32[4]; +typedef char __pad_after_u32[0]; #endif
#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN) typedef char __pad_before_uframe[0]; typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)]; +typedef char __pad_before_u32[0]; +typedef char __pad_after_u32[4]; #endif
I think these should remain unchanged, the complex expression was intentionally done so the structures are laid out the same way on 64-bit architectures, so that the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit and 64-bit architectures.
@@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream, memset(&sync_ptr, 0, sizeof(sync_ptr)); if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags))) return -EFAULT;
if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))return -EFAULT;
if (buggy_control) {if (copy_from_user(&sync_ptr.c.control_api_2_0_15,&(_sync_ptr->c.control_api_2_0_15),sizeof(sync_ptr.c.control_api_2_0_15)))return -EFAULT;} else {if (copy_from_user(&sync_ptr.c.control,&(_sync_ptr->c.control),sizeof(sync_ptr.c.control)))return -EFAULT;}The problem I see with this is that it might break musl's ability to emulate the new interface on top of the old (time32) one for linux-4.x and older kernels, as the conversion function is no longer stateless but has to know the negotiated interface version.
It's probably fine as long as we can be sure that the 2.0.16+ API version only gets negotiated if both the kernel and user sides support it, and musl only emulates the 2.0.15 API version from the current kernels.
I've tried to understand this part of musl's convert_ioctl_struct(), but I just can't figure out whether it does the conversion based the on the layout that is currently used in the kernel, or based on the layout we should have been using, and would use with the above fix. Rich, can you help me here?
If the attempted 64-bit ioctl is missing (ENOTTY), it does the conversion to the legacy 32-bit one and retries with that, then converts the results back to the 64-bit form.
Not only do I fail to see how the proposed fix is workable with this framework; I also don't see how the proposed fix would let new applications (compiled without the buggy type) run on old kernels. I'm pretty sure there really should be a new ioctl number for this...
Rich