pcm_native: result of put_user() needs to be checked

... and no, __put_user() doesn't help here - skipping
access_ok() on the second call does not remove the
possibility of page having become unmapped or r/o
in the meanwhile

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

sound/core/pcm_native.c

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 336406b..3943f9a 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -3087,7 +3087,8 @@ static int snd_pcm_xferi_frames_ioctl(struct snd_pcm_substream *substream,
 		result = snd_pcm_lib_write(substream, xferi.buf, xferi.frames);
 	else
 		result = snd_pcm_lib_read(substream, xferi.buf, xferi.frames);
-	__put_user(result, &_xferi->result);
+	if (put_user(result, &_xferi->result))
+		return -EFAULT;
 	return result < 0 ? result : 0;
 }
 
@@ -3116,7 +3117,8 @@ static int snd_pcm_xfern_frames_ioctl(struct snd_pcm_substream *substream,
 	else
 		result = snd_pcm_lib_readv(substream, bufs, xfern.frames);
 	kfree(bufs);
-	__put_user(result, &_xfern->result);
+	if (put_user(result, &_xfern->result))
+		return -EFAULT;
 	return result < 0 ? result : 0;
 }
 
@@ -3131,7 +3133,8 @@ static int snd_pcm_rewind_ioctl(struct snd_pcm_substream *substream,
 	if (put_user(0, _frames))
 		return -EFAULT;
 	result = snd_pcm_rewind(substream, frames);
-	__put_user(result, _frames);
+	if (put_user(result, _frames))
+		return -EFAULT;
 	return result < 0 ? result : 0;
 }
 
@@ -3146,7 +3149,8 @@ static int snd_pcm_forward_ioctl(struct snd_pcm_substream *substream,
 	if (put_user(0, _frames))
 		return -EFAULT;
 	result = snd_pcm_forward(substream, frames);
-	__put_user(result, _frames);
+	if (put_user(result, _frames))
+		return -EFAULT;
 	return result < 0 ? result : 0;
 }