ACK: [SRU][Trusty][PATCH 1/1] ALSA: seq: Fix use-after-free at creating a port
Stefan Bader
stefan.bader at canonical.com
Fri Jun 8 13:58:04 UTC 2018
On 07.06.2018 16:28, Kleber Sacilotto de Souza wrote:
> From: Takashi Iwai <tiwai at 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 at gmail.com>
> Suggested-by: Linus Torvalds <torvalds at linux-foundation.org>
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>
>
> CVE-2017-15265
> (backported from commit 71105998845fb012937332fe2e806d443c09e026)
> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
Acked-by: Stefan Bader <stefan.bader at 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;
> }
>
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