[alsa-devel] [PATCH] alsa-lib: Protect from freeing semaphore when already in use

[sutar.mounesh at gmail.com]

From: Joshua Frkuska <joshua_frkuska at mentor.com>

In the case of dshare, dsnoop, and dmix when a device is opened twice
and fails the second time, the semaphore is completely discarded. This
creates dangling semaphore data.

This patch removes the possibility for the semaphore to be destroyed during
a typical open failure by first checking if the shared memory can be destroyed
or not. If the shared memory cannot be released it means both it and the
semaphore are still in use and therefore the semaphore is just released.

Signed-off-by: Joshua Frkuska <joshua_frkuska at mentor.com>
---
 src/pcm/pcm_dmix.c   |    7 ++++---
 src/pcm/pcm_dshare.c |    7 ++++---
 src/pcm/pcm_dsnoop.c |    8 +++++---
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/src/pcm/pcm_dmix.c b/src/pcm/pcm_dmix.c
index 2bd5d39..b17f759 100644
--- a/src/pcm/pcm_dmix.c
+++ b/src/pcm/pcm_dmix.c
@@ -1128,9 +1128,10 @@ int snd_pcm_dmix_open(snd_pcm_t **pcmp, const char *name,
 		snd_pcm_close(spcm);
 	if (dmix->u.dmix.shmid_sum >= 0)
 		shm_sum_discard(dmix);
-	if (dmix->shmid >= 0)
-		snd_pcm_direct_shm_discard(dmix);
-	if (snd_pcm_direct_semaphore_discard(dmix) < 0)
+	if ((dmix->shmid >= 0) && (snd_pcm_direct_shm_discard(dmix))) {
+		if (snd_pcm_direct_semaphore_discard(dmix))
+			snd_pcm_direct_semaphore_final(dmix, DIRECT_IPC_SEM_CLIENT);
+	} else
 		snd_pcm_direct_semaphore_up(dmix, DIRECT_IPC_SEM_CLIENT);
  _err_nosem:
 	if (dmix) {
diff --git a/src/pcm/pcm_dshare.c b/src/pcm/pcm_dshare.c
index 5b32951..c080e7a 100644
--- a/src/pcm/pcm_dshare.c
+++ b/src/pcm/pcm_dshare.c
@@ -813,9 +813,10 @@ int snd_pcm_dshare_open(snd_pcm_t **pcmp, const char *name,
 		snd_pcm_direct_client_discard(dshare);
 	if (spcm)
 		snd_pcm_close(spcm);
-	if (dshare->shmid >= 0)
-		snd_pcm_direct_shm_discard(dshare);
-	if (snd_pcm_direct_semaphore_discard(dshare) < 0)
+	if ((dshare->shmid >= 0) && (snd_pcm_direct_shm_discard(dshare))) {
+		if (snd_pcm_direct_semaphore_discard(dshare))
+			snd_pcm_direct_semaphore_final(dshare, DIRECT_IPC_SEM_CLIENT);
+	} else
 		snd_pcm_direct_semaphore_up(dshare, DIRECT_IPC_SEM_CLIENT);
  _err_nosem:
 	if (dshare) {
diff --git a/src/pcm/pcm_dsnoop.c b/src/pcm/pcm_dsnoop.c
index 055e4f4..74a3531 100644
--- a/src/pcm/pcm_dsnoop.c
+++ b/src/pcm/pcm_dsnoop.c
@@ -712,10 +712,12 @@ int snd_pcm_dsnoop_open(snd_pcm_t **pcmp, const char *name,
 		snd_pcm_direct_client_discard(dsnoop);
 	if (spcm)
 		snd_pcm_close(spcm);
-	if (dsnoop->shmid >= 0)
-		snd_pcm_direct_shm_discard(dsnoop);
-	if (snd_pcm_direct_semaphore_discard(dsnoop) < 0)
+	if ((dsnoop->shmid >= 0) && (snd_pcm_direct_shm_discard(dsnoop))) {
+		if (snd_pcm_direct_semaphore_discard(dsnoop))
+			snd_pcm_direct_semaphore_final(dsnoop, DIRECT_IPC_SEM_CLIENT);
+	} else
 		snd_pcm_direct_semaphore_up(dsnoop, DIRECT_IPC_SEM_CLIENT);
+
  _err_nosem:
 	if (dsnoop) {
 		free(dsnoop->bindings);
-- 
1.7.9.5