On Wed, 23 Nov 2022 08:06:16 +0100, butt3rflyh4ck wrote:

Hi, the compat_status structure is struct compat_snd_rawmidi_status64 { s32 stream; u8 rsvd[4]; /* alignment */ s64 tstamp_sec; s64 tstamp_nsec; u32 avail; u32 xruns; unsigned char reserved[16]; } __attribute__((packed)); The rsvd[4] and reserved[16] are not initialized.

Other members are initialized with zero. https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html

Takashi

Regards, butt3rflyh4ck.

On Wed, Nov 23, 2022 at 2:55 PM Takashi Iwai tiwai@suse.de wrote:

...

On Wed, 23 Nov 2022 06:09:11 +0100, Xiaolong Huang wrote:

...

The compat_status is declared off of the stack, so it needs to be zeroed out before copied back to userspace to prevent any unintentional data leakage.

Fixes: d9e5582c4bb2 ("ALSA: Avoid using timespec for struct snd_rawmidi_status") Signed-off-by: Xiaolong Huang butterflyhuangxx@gmail.com

---

Reason for resend:

1. add Fixes line.

---

sound/core/rawmidi_compat.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/sound/core/rawmidi_compat.c b/sound/core/rawmidi_compat.c index 68a93443583c..6afa68165b17 100644 --- a/sound/core/rawmidi_compat.c +++ b/sound/core/rawmidi_compat.c @@ -80,6 +80,7 @@ static int snd_rawmidi_ioctl_status_compat64(struct snd_rawmidi_file *rfile, if (err < 0) return err;

• memset(&compat_status, 0, sizeof(compat_status));
  compat_status = (struct compat_snd_rawmidi_status64) {
          .stream = status.stream,
          .tstamp_sec = status.tstamp_sec,
  

Here at the line just after your addition, compat_status is fully initialized by substitution, so I believe the memset is superfluous.

Or have you verified that it really leaks the uninitialized memory?

thanks,

Takashi

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