ALSA: seq: Fix racy cell insertions during snd_seq_pool_done()

When snd_seq_pool_done() is called, it marks the closing flag to
refuse the further cell insertions.  But snd_seq_pool_done() itself
doesn't clear the cells but just waits until all cells are cleared by
the caller side.  That is, it's racy, and this leads to the endless
stall as syzkaller spotted.

This patch addresses the racy by splitting the setup of pool->closing
flag out of snd_seq_pool_done(), and calling it properly before
snd_seq_pool_done().

BugLink: http://lkml.kernel.org/r/CACT4Y+aqqy8bZA1fFieifNxR2fAfFQQABcBHj801+u5ePV0URw@mail.gmail.com
Reported-and-tested-by: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index 4c935202ce23be4fc57c9d79c3fe0a160d9b8a89..f3b1d7f50b81156d4c29c5c0958a884e9292bbae 100644 (file)
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1832,6 +1832,7 @@ static int snd_seq_ioctl_set_client_pool(struct snd_seq_client *client,
             info->output_pool != client->pool->size)) {
                if (snd_seq_write_pool_allocated(client)) {
                        /* remove all existing cells */
+                       snd_seq_pool_mark_closing(client->pool);
                        snd_seq_queue_client_leave_cells(client->number);
                        snd_seq_pool_done(client->pool);
                }

diff --git a/sound/core/seq/seq_fifo.c b/sound/core/seq/seq_fifo.c
index 448efd4e980edf97138b43b6263a9909d07c076a..33980d1c803796a3a77cf2ee69c35a9b5fcf1c9e 100644 (file)
--- a/sound/core/seq/seq_fifo.c
+++ b/sound/core/seq/seq_fifo.c
@@ -72,6 +72,9 @@ void snd_seq_fifo_delete(struct snd_seq_fifo **fifo)
                return;
        *fifo = NULL;
 
+       if (f->pool)
+               snd_seq_pool_mark_closing(f->pool);
+
        snd_seq_fifo_clear(f);
 
        /* wake up clients if any */

diff --git a/sound/core/seq/seq_memory.c b/sound/core/seq/seq_memory.c
index 1a1acf3ddda4c9aeb022548b9438498e0f036762..d4c61ec9be13d7389addd27bc70acf58bda2eecc 100644 (file)
--- a/sound/core/seq/seq_memory.c
+++ b/sound/core/seq/seq_memory.c
@@ -415,6 +415,18 @@ int snd_seq_pool_init(struct snd_seq_pool *pool)
        return 0;
 }
 
+/* refuse the further insertion to the pool */
+void snd_seq_pool_mark_closing(struct snd_seq_pool *pool)
+{
+       unsigned long flags;
+
+       if (snd_BUG_ON(!pool))
+               return;
+       spin_lock_irqsave(&pool->lock, flags);
+       pool->closing = 1;
+       spin_unlock_irqrestore(&pool->lock, flags);
+}
+
 /* remove events */
 int snd_seq_pool_done(struct snd_seq_pool *pool)
 {
@@ -425,10 +437,6 @@ int snd_seq_pool_done(struct snd_seq_pool *pool)
                return -EINVAL;
 
        /* wait for closing all threads */
-       spin_lock_irqsave(&pool->lock, flags);
-       pool->closing = 1;
-       spin_unlock_irqrestore(&pool->lock, flags);
-
        if (waitqueue_active(&pool->output_sleep))
                wake_up(&pool->output_sleep);
 
@@ -485,6 +493,7 @@ int snd_seq_pool_delete(struct snd_seq_pool **ppool)
        *ppool = NULL;
        if (pool == NULL)
                return 0;
+       snd_seq_pool_mark_closing(pool);
        snd_seq_pool_done(pool);
        kfree(pool);
        return 0;

diff --git a/sound/core/seq/seq_memory.h b/sound/core/seq/seq_memory.h
index 4a2ec779b8a701b1aba2402e9de583878f7a39ca..32f959c17786d9ac8c071ba0e6fd070dc06da78b 100644 (file)
--- a/sound/core/seq/seq_memory.h
+++ b/sound/core/seq/seq_memory.h
@@ -84,6 +84,7 @@ static inline int snd_seq_total_cells(struct snd_seq_pool *pool)
 int snd_seq_pool_init(struct snd_seq_pool *pool);
 
 /* done pool - free events */
+void snd_seq_pool_mark_closing(struct snd_seq_pool *pool);
 int snd_seq_pool_done(struct snd_seq_pool *pool);
 
 /* create pool */