[SRU,Trusty,1/1] ALSA: seq: Fix use-after-free at creating a port

Message ID 20180607232856.28995-2-kleber.souza@canonical.com
State New
Headers show
Series
  • Fix for CVE-2017-15265
Related show

Commit Message

Kleber Souza June 7, 2018, 11:28 p.m.
From: Takashi Iwai <tiwai@suse.de>

There is a potential race window opened at creating and deleting a
port via ioctl, as spotted by fuzzing.  snd_seq_create_port() creates
a port object and returns its pointer, but it doesn't take the
refcount, thus it can be deleted immediately by another thread.
Meanwhile, snd_seq_ioctl_create_port() still calls the function
snd_seq_system_client_ev_port_start() with the created port object
that is being deleted, and this triggers use-after-free like:

 BUG: KASAN: use-after-free in snd_seq_ioctl_create_port+0x504/0x630 [snd_seq] at addr ffff8801f2241cb1
 =============================================================================
 BUG kmalloc-512 (Tainted: G    B          ): kasan: bad access detected
 -----------------------------------------------------------------------------
 INFO: Allocated in snd_seq_create_port+0x94/0x9b0 [snd_seq] age=1 cpu=3 pid=4511
 	___slab_alloc+0x425/0x460
 	__slab_alloc+0x20/0x40
  	kmem_cache_alloc_trace+0x150/0x190
	snd_seq_create_port+0x94/0x9b0 [snd_seq]
	snd_seq_ioctl_create_port+0xd1/0x630 [snd_seq]
 	snd_seq_do_ioctl+0x11c/0x190 [snd_seq]
 	snd_seq_ioctl+0x40/0x80 [snd_seq]
 	do_vfs_ioctl+0x54b/0xda0
 	SyS_ioctl+0x79/0x90
 	entry_SYSCALL_64_fastpath+0x16/0x75
 INFO: Freed in port_delete+0x136/0x1a0 [snd_seq] age=1 cpu=2 pid=4717
 	__slab_free+0x204/0x310
 	kfree+0x15f/0x180
 	port_delete+0x136/0x1a0 [snd_seq]
 	snd_seq_delete_port+0x235/0x350 [snd_seq]
 	snd_seq_ioctl_delete_port+0xc8/0x180 [snd_seq]
 	snd_seq_do_ioctl+0x11c/0x190 [snd_seq]
 	snd_seq_ioctl+0x40/0x80 [snd_seq]
 	do_vfs_ioctl+0x54b/0xda0
 	SyS_ioctl+0x79/0x90
 	entry_SYSCALL_64_fastpath+0x16/0x75
 Call Trace:
  [<ffffffff81b03781>] dump_stack+0x63/0x82
  [<ffffffff81531b3b>] print_trailer+0xfb/0x160
  [<ffffffff81536db4>] object_err+0x34/0x40
  [<ffffffff815392d3>] kasan_report.part.2+0x223/0x520
  [<ffffffffa07aadf4>] ? snd_seq_ioctl_create_port+0x504/0x630 [snd_seq]
  [<ffffffff815395fe>] __asan_report_load1_noabort+0x2e/0x30
  [<ffffffffa07aadf4>] snd_seq_ioctl_create_port+0x504/0x630 [snd_seq]
  [<ffffffffa07aa8f0>] ? snd_seq_ioctl_delete_port+0x180/0x180 [snd_seq]
  [<ffffffff8136be50>] ? taskstats_exit+0xbc0/0xbc0
  [<ffffffffa07abc5c>] snd_seq_do_ioctl+0x11c/0x190 [snd_seq]
  [<ffffffffa07abd10>] snd_seq_ioctl+0x40/0x80 [snd_seq]
  [<ffffffff8136d433>] ? acct_account_cputime+0x63/0x80
  [<ffffffff815b515b>] do_vfs_ioctl+0x54b/0xda0
  .....

We may fix this in a few different ways, and in this patch, it's fixed
simply by taking the refcount properly at snd_seq_create_port() and
letting the caller unref the object after use.  Also, there is another
potential use-after-free by sprintf() call in snd_seq_create_port(),
and this is moved inside the lock.

This fix covers CVE-2017-15265.

Reported-and-tested-by: Michael23 Yu <ycqzsy@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

CVE-2017-15265
(backported from commit 71105998845fb012937332fe2e806d443c09e026)
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
---
 sound/core/seq/seq_clientmgr.c | 6 +++++-
 sound/core/seq/seq_ports.c     | 7 +++++--
 2 files changed, 10 insertions(+), 3 deletions(-)

Comments

Stefan Bader June 8, 2018, 1:58 p.m. | #1
On 07.06.2018 16:28, Kleber Sacilotto de Souza wrote:
> From: Takashi Iwai <tiwai@suse.de>
> 
> There is a potential race window opened at creating and deleting a
> port via ioctl, as spotted by fuzzing.  snd_seq_create_port() creates
> a port object and returns its pointer, but it doesn't take the
> refcount, thus it can be deleted immediately by another thread.
> Meanwhile, snd_seq_ioctl_create_port() still calls the function
> snd_seq_system_client_ev_port_start() with the created port object
> that is being deleted, and this triggers use-after-free like:
> 
>  BUG: KASAN: use-after-free in snd_seq_ioctl_create_port+0x504/0x630 [snd_seq] at addr ffff8801f2241cb1
>  =============================================================================
>  BUG kmalloc-512 (Tainted: G    B          ): kasan: bad access detected
>  -----------------------------------------------------------------------------
>  INFO: Allocated in snd_seq_create_port+0x94/0x9b0 [snd_seq] age=1 cpu=3 pid=4511
>  	___slab_alloc+0x425/0x460
>  	__slab_alloc+0x20/0x40
>   	kmem_cache_alloc_trace+0x150/0x190
> 	snd_seq_create_port+0x94/0x9b0 [snd_seq]
> 	snd_seq_ioctl_create_port+0xd1/0x630 [snd_seq]
>  	snd_seq_do_ioctl+0x11c/0x190 [snd_seq]
>  	snd_seq_ioctl+0x40/0x80 [snd_seq]
>  	do_vfs_ioctl+0x54b/0xda0
>  	SyS_ioctl+0x79/0x90
>  	entry_SYSCALL_64_fastpath+0x16/0x75
>  INFO: Freed in port_delete+0x136/0x1a0 [snd_seq] age=1 cpu=2 pid=4717
>  	__slab_free+0x204/0x310
>  	kfree+0x15f/0x180
>  	port_delete+0x136/0x1a0 [snd_seq]
>  	snd_seq_delete_port+0x235/0x350 [snd_seq]
>  	snd_seq_ioctl_delete_port+0xc8/0x180 [snd_seq]
>  	snd_seq_do_ioctl+0x11c/0x190 [snd_seq]
>  	snd_seq_ioctl+0x40/0x80 [snd_seq]
>  	do_vfs_ioctl+0x54b/0xda0
>  	SyS_ioctl+0x79/0x90
>  	entry_SYSCALL_64_fastpath+0x16/0x75
>  Call Trace:
>   [<ffffffff81b03781>] dump_stack+0x63/0x82
>   [<ffffffff81531b3b>] print_trailer+0xfb/0x160
>   [<ffffffff81536db4>] object_err+0x34/0x40
>   [<ffffffff815392d3>] kasan_report.part.2+0x223/0x520
>   [<ffffffffa07aadf4>] ? snd_seq_ioctl_create_port+0x504/0x630 [snd_seq]
>   [<ffffffff815395fe>] __asan_report_load1_noabort+0x2e/0x30
>   [<ffffffffa07aadf4>] snd_seq_ioctl_create_port+0x504/0x630 [snd_seq]
>   [<ffffffffa07aa8f0>] ? snd_seq_ioctl_delete_port+0x180/0x180 [snd_seq]
>   [<ffffffff8136be50>] ? taskstats_exit+0xbc0/0xbc0
>   [<ffffffffa07abc5c>] snd_seq_do_ioctl+0x11c/0x190 [snd_seq]
>   [<ffffffffa07abd10>] snd_seq_ioctl+0x40/0x80 [snd_seq]
>   [<ffffffff8136d433>] ? acct_account_cputime+0x63/0x80
>   [<ffffffff815b515b>] do_vfs_ioctl+0x54b/0xda0
>   .....
> 
> We may fix this in a few different ways, and in this patch, it's fixed
> simply by taking the refcount properly at snd_seq_create_port() and
> letting the caller unref the object after use.  Also, there is another
> potential use-after-free by sprintf() call in snd_seq_create_port(),
> and this is moved inside the lock.
> 
> This fix covers CVE-2017-15265.
> 
> Reported-and-tested-by: Michael23 Yu <ycqzsy@gmail.com>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> 
> CVE-2017-15265
> (backported from commit 71105998845fb012937332fe2e806d443c09e026)
> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
> ---
>  sound/core/seq/seq_clientmgr.c | 6 +++++-
>  sound/core/seq/seq_ports.c     | 7 +++++--
>  2 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
> index 08865dcbf5f1..750e4a975379 100644
> --- a/sound/core/seq/seq_clientmgr.c
> +++ b/sound/core/seq/seq_clientmgr.c
> @@ -1248,6 +1248,7 @@ static int snd_seq_ioctl_create_port(struct snd_seq_client *client,
>  	struct snd_seq_client_port *port;
>  	struct snd_seq_port_info info;
>  	struct snd_seq_port_callback *callback;
> +	int port_idx;
>  
>  	if (copy_from_user(&info, arg, sizeof(info)))
>  		return -EFAULT;
> @@ -1261,7 +1262,9 @@ static int snd_seq_ioctl_create_port(struct snd_seq_client *client,
>  		return -ENOMEM;
>  
>  	if (client->type == USER_CLIENT && info.kernel) {
> -		snd_seq_delete_port(client, port->addr.port);
> +		port_idx = port->addr.port;
> +		snd_seq_port_unlock(port);
> +		snd_seq_delete_port(client, port_idx);
>  		return -EINVAL;
>  	}
>  	if (client->type == KERNEL_CLIENT) {
> @@ -1283,6 +1286,7 @@ static int snd_seq_ioctl_create_port(struct snd_seq_client *client,
>  
>  	snd_seq_set_port_info(port, &info);
>  	snd_seq_system_client_ev_port_start(port->addr.client, port->addr.port);
> +	snd_seq_port_unlock(port);
>  
>  	if (copy_to_user(arg, &info, sizeof(info)))
>  		return -EFAULT;
> diff --git a/sound/core/seq/seq_ports.c b/sound/core/seq/seq_ports.c
> index 0cb3c28b7a3e..7960f898f37b 100644
> --- a/sound/core/seq/seq_ports.c
> +++ b/sound/core/seq/seq_ports.c
> @@ -122,7 +122,9 @@ static void port_subs_info_init(struct snd_seq_port_subs_info *grp)
>  }
>  
>  
> -/* create a port, port number is returned (-1 on failure) */
> +/* create a port, port number is returned (-1 on failure);
> + * the caller needs to unref the port via snd_seq_port_unlock() appropriately
> + */
>  struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
>  						int port)
>  {
> @@ -151,6 +153,7 @@ struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
>  	snd_use_lock_init(&new_port->use_lock);
>  	port_subs_info_init(&new_port->c_src);
>  	port_subs_info_init(&new_port->c_dest);
> +	snd_use_lock_use(&new_port->use_lock);
>  
>  	num = port >= 0 ? port : 0;
>  	mutex_lock(&client->ports_mutex);
> @@ -165,9 +168,9 @@ struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
>  	list_add_tail(&new_port->list, &p->list);
>  	client->num_ports++;
>  	new_port->addr.port = num;	/* store the port number in the port */
> +	sprintf(new_port->name, "port-%d", num);
>  	write_unlock_irqrestore(&client->ports_lock, flags);
>  	mutex_unlock(&client->ports_mutex);
> -	sprintf(new_port->name, "port-%d", num);
>  
>  	return new_port;
>  }
>
Andy Whitcroft June 8, 2018, 2:39 p.m. | #2
On Thu, Jun 07, 2018 at 04:28:56PM -0700, Kleber Sacilotto de Souza wrote:
> From: Takashi Iwai <tiwai@suse.de>
> 
> There is a potential race window opened at creating and deleting a
> port via ioctl, as spotted by fuzzing.  snd_seq_create_port() creates
> a port object and returns its pointer, but it doesn't take the
> refcount, thus it can be deleted immediately by another thread.
> Meanwhile, snd_seq_ioctl_create_port() still calls the function
> snd_seq_system_client_ev_port_start() with the created port object
> that is being deleted, and this triggers use-after-free like:
> 
>  BUG: KASAN: use-after-free in snd_seq_ioctl_create_port+0x504/0x630 [snd_seq] at addr ffff8801f2241cb1
>  =============================================================================
>  BUG kmalloc-512 (Tainted: G    B          ): kasan: bad access detected
>  -----------------------------------------------------------------------------
>  INFO: Allocated in snd_seq_create_port+0x94/0x9b0 [snd_seq] age=1 cpu=3 pid=4511
>  	___slab_alloc+0x425/0x460
>  	__slab_alloc+0x20/0x40
>   	kmem_cache_alloc_trace+0x150/0x190
> 	snd_seq_create_port+0x94/0x9b0 [snd_seq]
> 	snd_seq_ioctl_create_port+0xd1/0x630 [snd_seq]
>  	snd_seq_do_ioctl+0x11c/0x190 [snd_seq]
>  	snd_seq_ioctl+0x40/0x80 [snd_seq]
>  	do_vfs_ioctl+0x54b/0xda0
>  	SyS_ioctl+0x79/0x90
>  	entry_SYSCALL_64_fastpath+0x16/0x75
>  INFO: Freed in port_delete+0x136/0x1a0 [snd_seq] age=1 cpu=2 pid=4717
>  	__slab_free+0x204/0x310
>  	kfree+0x15f/0x180
>  	port_delete+0x136/0x1a0 [snd_seq]
>  	snd_seq_delete_port+0x235/0x350 [snd_seq]
>  	snd_seq_ioctl_delete_port+0xc8/0x180 [snd_seq]
>  	snd_seq_do_ioctl+0x11c/0x190 [snd_seq]
>  	snd_seq_ioctl+0x40/0x80 [snd_seq]
>  	do_vfs_ioctl+0x54b/0xda0
>  	SyS_ioctl+0x79/0x90
>  	entry_SYSCALL_64_fastpath+0x16/0x75
>  Call Trace:
>   [<ffffffff81b03781>] dump_stack+0x63/0x82
>   [<ffffffff81531b3b>] print_trailer+0xfb/0x160
>   [<ffffffff81536db4>] object_err+0x34/0x40
>   [<ffffffff815392d3>] kasan_report.part.2+0x223/0x520
>   [<ffffffffa07aadf4>] ? snd_seq_ioctl_create_port+0x504/0x630 [snd_seq]
>   [<ffffffff815395fe>] __asan_report_load1_noabort+0x2e/0x30
>   [<ffffffffa07aadf4>] snd_seq_ioctl_create_port+0x504/0x630 [snd_seq]
>   [<ffffffffa07aa8f0>] ? snd_seq_ioctl_delete_port+0x180/0x180 [snd_seq]
>   [<ffffffff8136be50>] ? taskstats_exit+0xbc0/0xbc0
>   [<ffffffffa07abc5c>] snd_seq_do_ioctl+0x11c/0x190 [snd_seq]
>   [<ffffffffa07abd10>] snd_seq_ioctl+0x40/0x80 [snd_seq]
>   [<ffffffff8136d433>] ? acct_account_cputime+0x63/0x80
>   [<ffffffff815b515b>] do_vfs_ioctl+0x54b/0xda0
>   .....
> 
> We may fix this in a few different ways, and in this patch, it's fixed
> simply by taking the refcount properly at snd_seq_create_port() and
> letting the caller unref the object after use.  Also, there is another
> potential use-after-free by sprintf() call in snd_seq_create_port(),
> and this is moved inside the lock.
> 
> This fix covers CVE-2017-15265.
> 
> Reported-and-tested-by: Michael23 Yu <ycqzsy@gmail.com>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> 
> CVE-2017-15265
> (backported from commit 71105998845fb012937332fe2e806d443c09e026)
> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
> ---
>  sound/core/seq/seq_clientmgr.c | 6 +++++-
>  sound/core/seq/seq_ports.c     | 7 +++++--
>  2 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
> index 08865dcbf5f1..750e4a975379 100644
> --- a/sound/core/seq/seq_clientmgr.c
> +++ b/sound/core/seq/seq_clientmgr.c
> @@ -1248,6 +1248,7 @@ static int snd_seq_ioctl_create_port(struct snd_seq_client *client,
>  	struct snd_seq_client_port *port;
>  	struct snd_seq_port_info info;
>  	struct snd_seq_port_callback *callback;
> +	int port_idx;
>  
>  	if (copy_from_user(&info, arg, sizeof(info)))
>  		return -EFAULT;
> @@ -1261,7 +1262,9 @@ static int snd_seq_ioctl_create_port(struct snd_seq_client *client,
>  		return -ENOMEM;
>  
>  	if (client->type == USER_CLIENT && info.kernel) {
> -		snd_seq_delete_port(client, port->addr.port);
> +		port_idx = port->addr.port;
> +		snd_seq_port_unlock(port);
> +		snd_seq_delete_port(client, port_idx);
>  		return -EINVAL;
>  	}
>  	if (client->type == KERNEL_CLIENT) {
> @@ -1283,6 +1286,7 @@ static int snd_seq_ioctl_create_port(struct snd_seq_client *client,
>  
>  	snd_seq_set_port_info(port, &info);
>  	snd_seq_system_client_ev_port_start(port->addr.client, port->addr.port);
> +	snd_seq_port_unlock(port);
>  
>  	if (copy_to_user(arg, &info, sizeof(info)))
>  		return -EFAULT;
> diff --git a/sound/core/seq/seq_ports.c b/sound/core/seq/seq_ports.c
> index 0cb3c28b7a3e..7960f898f37b 100644
> --- a/sound/core/seq/seq_ports.c
> +++ b/sound/core/seq/seq_ports.c
> @@ -122,7 +122,9 @@ static void port_subs_info_init(struct snd_seq_port_subs_info *grp)
>  }
>  
>  
> -/* create a port, port number is returned (-1 on failure) */
> +/* create a port, port number is returned (-1 on failure);
> + * the caller needs to unref the port via snd_seq_port_unlock() appropriately
> + */
>  struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
>  						int port)
>  {
> @@ -151,6 +153,7 @@ struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
>  	snd_use_lock_init(&new_port->use_lock);
>  	port_subs_info_init(&new_port->c_src);
>  	port_subs_info_init(&new_port->c_dest);
> +	snd_use_lock_use(&new_port->use_lock);
>  
>  	num = port >= 0 ? port : 0;
>  	mutex_lock(&client->ports_mutex);
> @@ -165,9 +168,9 @@ struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
>  	list_add_tail(&new_port->list, &p->list);
>  	client->num_ports++;
>  	new_port->addr.port = num;	/* store the port number in the port */
> +	sprintf(new_port->name, "port-%d", num);
>  	write_unlock_irqrestore(&client->ports_lock, flags);
>  	mutex_unlock(&client->ports_mutex);
> -	sprintf(new_port->name, "port-%d", num);
>  
>  	return new_port;
>  }

Looks to do what is claimed.

Acked-by: Andy Whitcroft <apw@canonical.com>

-apw

Patch

diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index 08865dcbf5f1..750e4a975379 100644
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1248,6 +1248,7 @@  static int snd_seq_ioctl_create_port(struct snd_seq_client *client,
 	struct snd_seq_client_port *port;
 	struct snd_seq_port_info info;
 	struct snd_seq_port_callback *callback;
+	int port_idx;
 
 	if (copy_from_user(&info, arg, sizeof(info)))
 		return -EFAULT;
@@ -1261,7 +1262,9 @@  static int snd_seq_ioctl_create_port(struct snd_seq_client *client,
 		return -ENOMEM;
 
 	if (client->type == USER_CLIENT && info.kernel) {
-		snd_seq_delete_port(client, port->addr.port);
+		port_idx = port->addr.port;
+		snd_seq_port_unlock(port);
+		snd_seq_delete_port(client, port_idx);
 		return -EINVAL;
 	}
 	if (client->type == KERNEL_CLIENT) {
@@ -1283,6 +1286,7 @@  static int snd_seq_ioctl_create_port(struct snd_seq_client *client,
 
 	snd_seq_set_port_info(port, &info);
 	snd_seq_system_client_ev_port_start(port->addr.client, port->addr.port);
+	snd_seq_port_unlock(port);
 
 	if (copy_to_user(arg, &info, sizeof(info)))
 		return -EFAULT;
diff --git a/sound/core/seq/seq_ports.c b/sound/core/seq/seq_ports.c
index 0cb3c28b7a3e..7960f898f37b 100644
--- a/sound/core/seq/seq_ports.c
+++ b/sound/core/seq/seq_ports.c
@@ -122,7 +122,9 @@  static void port_subs_info_init(struct snd_seq_port_subs_info *grp)
 }
 
 
-/* create a port, port number is returned (-1 on failure) */
+/* create a port, port number is returned (-1 on failure);
+ * the caller needs to unref the port via snd_seq_port_unlock() appropriately
+ */
 struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
 						int port)
 {
@@ -151,6 +153,7 @@  struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
 	snd_use_lock_init(&new_port->use_lock);
 	port_subs_info_init(&new_port->c_src);
 	port_subs_info_init(&new_port->c_dest);
+	snd_use_lock_use(&new_port->use_lock);
 
 	num = port >= 0 ? port : 0;
 	mutex_lock(&client->ports_mutex);
@@ -165,9 +168,9 @@  struct snd_seq_client_port *snd_seq_create_port(struct snd_seq_client *client,
 	list_add_tail(&new_port->list, &p->list);
 	client->num_ports++;
 	new_port->addr.port = num;	/* store the port number in the port */
+	sprintf(new_port->name, "port-%d", num);
 	write_unlock_irqrestore(&client->ports_lock, flags);
 	mutex_unlock(&client->ports_mutex);
-	sprintf(new_port->name, "port-%d", num);
 
 	return new_port;
 }