From: Anirudh Rayabharam mail@anirudhrb.com

stable inclusion from stable-v4.19.187 commit 92028d7a31e55d53e41cff679156b9432cffcb36 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/I93LMH CVE: CVE-2021-46904

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...

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commit 8a12f8836145ffe37e9c8733dce18c22fb668b66 upstream.

Multiple ttys try to claim the same the minor number causing a double unregistration of the same device. The first unregistration succeeds but the next one results in a null-ptr-deref.

The get_free_serial_index() function returns an available minor number but doesn't assign it immediately. The assignment is done by the caller later. But before this assignment, calls to get_free_serial_index() would return the same minor number.

Fix this by modifying get_free_serial_index to assign the minor number immediately after one is found to be and rename it to obtain_minor() to better reflect what it does. Similary, rename set_serial_by_index() to release_minor() and modify it to free up the minor number of the given hso_serial. Every obtain_minor() should have corresponding release_minor() call.

Fixes: 72dc1c096c705 ("HSO: add option hso driver") Reported-by: syzbot+c49fe6089f295a05e6f8@syzkaller.appspotmail.com Tested-by: syzbot+c49fe6089f295a05e6f8@syzkaller.appspotmail.com Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Anirudh Rayabharam mail@anirudhrb.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Liu Jian liujian56@huawei.com --- drivers/net/usb/hso.c | 33 ++++++++++++--------------------- 1 file changed, 12 insertions(+), 21 deletions(-)

diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c index e026f89baa96..9a89089a6e08 100644 --- a/drivers/net/usb/hso.c +++ b/drivers/net/usb/hso.c @@ -625,7 +625,7 @@ static struct hso_serial *get_serial_by_index(unsigned index) return serial; }

-static int get_free_serial_index(void) +static int obtain_minor(struct hso_serial *serial) { int index; unsigned long flags; @@ -633,8 +633,10 @@ static int get_free_serial_index(void) spin_lock_irqsave(&serial_table_lock, flags); for (index = 0; index < HSO_SERIAL_TTY_MINORS; index++) { if (serial_table[index] == NULL) { + serial_table[index] = serial->parent; + serial->minor = index; spin_unlock_irqrestore(&serial_table_lock, flags); - return index; + return 0; } } spin_unlock_irqrestore(&serial_table_lock, flags); @@ -643,15 +645,12 @@ static int get_free_serial_index(void) return -1; }

-static void set_serial_by_index(unsigned index, struct hso_serial *serial) +static void release_minor(struct hso_serial *serial) { unsigned long flags;

spin_lock_irqsave(&serial_table_lock, flags); - if (serial) - serial_table[index] = serial->parent; - else - serial_table[index] = NULL; + serial_table[serial->minor] = NULL; spin_unlock_irqrestore(&serial_table_lock, flags); }

@@ -2243,6 +2242,7 @@ static int hso_stop_serial_device(struct hso_device *hso_dev) static void hso_serial_tty_unregister(struct hso_serial *serial) { tty_unregister_device(tty_drv, serial->minor); + release_minor(serial); }

static void hso_serial_common_free(struct hso_serial *serial) @@ -2266,24 +2266,22 @@ static void hso_serial_common_free(struct hso_serial *serial) static int hso_serial_common_create(struct hso_serial *serial, int num_urbs, int rx_size, int tx_size) { - int minor; int i;

tty_port_init(&serial->port);

- minor = get_free_serial_index(); - if (minor < 0) + if (obtain_minor(serial)) goto exit2;

/* register our minor number */ serial->parent->dev = tty_port_register_device_attr(&serial->port, - tty_drv, minor, &serial->parent->interface->dev, + tty_drv, serial->minor, &serial->parent->interface->dev, serial->parent, hso_serial_dev_groups); - if (IS_ERR(serial->parent->dev)) + if (IS_ERR(serial->parent->dev)) { + release_minor(serial); goto exit2; + }

- /* fill in specific data for later use */ - serial->minor = minor; serial->magic = HSO_SERIAL_MAGIC; spin_lock_init(&serial->serial_lock); serial->num_rx_urbs = num_urbs; @@ -2689,9 +2687,6 @@ static struct hso_device *hso_create_bulk_serial_device(

serial->write_data = hso_std_serial_write_data;

- /* and record this serial */ - set_serial_by_index(serial->minor, serial); - /* setup the proc dirs and files if needed */ hso_log_port(hso_dev);

@@ -2748,9 +2743,6 @@ struct hso_device *hso_create_mux_serial_device(struct usb_interface *interface, serial->shared_int->ref_count++; mutex_unlock(&serial->shared_int->shared_int_lock);

- /* and record this serial */ - set_serial_by_index(serial->minor, serial); - /* setup the proc dirs and files if needed */ hso_log_port(hso_dev);

@@ -3135,7 +3127,6 @@ static void hso_free_interface(struct usb_interface *interface) cancel_work_sync(&serial_table[i]->async_get_intf); hso_serial_tty_unregister(serial); kref_put(&serial_table[i]->ref, hso_serial_ref_free); - set_serial_by_index(i, NULL); } }