[alsa-devel] [PATCH] aplay: fix lurking capture file overwrite bug

[David Fries]

If -d was given to arecord while commit
8aa13eec80eac312e4b99423909387660fb99b8f (now reverted) was in effect,
the last read would be shorter than the chunk size, but pcm_read would
read and return the chunk size, the samples were discarded, and
capture() continued in a loop because count never reached 0.  arecord
opens a new file each loop iteration, if arecord is dynamically naming
files, --use-strftime option or beyond the wave 2GB limit, this will
generate a series of header only wave files.  If the file is unique
the originally recorded data is lost and it will continue overwriting
the same file with a header only wave file.

While the current pcm_read can't fail (it can exit), it is better to
just fix this lurking bug in case it is "fixed" again.
---
In my case I wanted to record for 16 hours, I did get the audio, but I
also found I had 3.1 million 44 byte files, which took the system
3 hours to unlink, I'm glad I at least discovered this problem the
next day..  Debian has the effectively broken pcm_read, after figuring
out what was going wrong, and that the current arecord doesn't exhibit
the problem I wanted to fix it anyway.  There are remaining problems,
pcm_read will read chunk_size, but if the requested size is smaller
samples are lost, I'm not trying to fix that here.  This will at least
gracefully close a wave file (update the counts) if read or write
returns a size different from requested.

 aplay/aplay.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/aplay/aplay.c b/aplay/aplay.c
index 7acaa83..2da7dda 100644
--- a/aplay/aplay.c
+++ b/aplay/aplay.c
@@ -3067,11 +3067,14 @@ static void capture(char *orig_name)
 			size_t c = (rest <= (off64_t)chunk_bytes) ?
 				(size_t)rest : chunk_bytes;
 			size_t f = c * 8 / bits_per_frame;
-			if (pcm_read(audiobuf, f) != f)
+			if (pcm_read(audiobuf, f) != f) {
+				in_aborting = 1;
 				break;
+			}
 			if (write(fd, audiobuf, c) != c) {
 				perror(name);
-				prg_exit(EXIT_FAILURE);
+				in_aborting = 1;
+				break;
 			}
 			count -= c;
 			rest -= c;
@@ -3091,7 +3094,7 @@ static void capture(char *orig_name)
 		}
 
 		if (in_aborting)
-			break;
+			prg_exit(EXIT_FAILURE);
 
 		/* repeat the loop when format is raw without timelimit or
 		 * requested counts of data are recorded
-- 
2.1.4