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

commit c520ff3d03f0b5db7146d9beed6373ad5d2a5e0e upstream.

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>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index 58e79e02f2174e29f409cf129030af87d240dfce..c67f9c212dd1f643f40b17ef755e5a2ef33e4339 100644 (file)
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1921,6 +1921,7 @@ 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 86240d02b530770f01d718eef34e2b4afeb2ff99..3f4efcb85df557b64ba2b074e56370ee9d047df8 100644 (file)
--- a/sound/core/seq/seq_fifo.c
+++ b/sound/core/seq/seq_fifo.c
@@ -70,6 +70,9 @@ 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 dfa5156f35856324d86f05315edfb2ef9cf4e74e..5847c4475bf31efe707032c9f370df9b245a7bba 100644 (file)
--- a/sound/core/seq/seq_memory.c
+++ b/sound/core/seq/seq_memory.c
@@ -414,6 +414,18 @@ 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)
 {
@@ -424,10 +436,6 @@ 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);
 
@@ -484,6 +492,7 @@ 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 */