path: root/drivers/firewire/core-cdev.c
diff options
authorStefan Richter <stefanr@s5r6.in-berlin.de>2011-07-09 16:43:22 +0200
committerStefan Richter <stefanr@s5r6.in-berlin.de>2011-07-16 07:24:32 +0200
commit93b37905f70083d6143f5f4dba0a45cc64379a62 (patch)
treeb6917581cd390ed9967e1df9922940362ad4309e /drivers/firewire/core-cdev.c
parentd873d794235efa590ab3c94d5ee22bb1fab19ac4 (diff)
firewire: cdev: prevent race between first get_info ioctl and bus reset event queuing
Between open(2) of a /dev/fw* and the first FW_CDEV_IOC_GET_INFO ioctl(2) on it, the kernel already queues FW_CDEV_EVENT_BUS_RESET events to be read(2) by the client. The get_info ioctl is practically always issued right away after open, hence this condition only occurs if the client opens during a bus reset, especially during a rapid series of bus resets. The problem with this condition is twofold: - These bus reset events carry the (as yet undocumented) @closure value of 0. But it is not the kernel's place to choose closures; they are privat to the client. E.g., this 0 value forced from the kernel makes it unsafe for clients to dereference it as a pointer to a closure object without NULL pointer check. - It is impossible for clients to determine the relative order of bus reset events from get_info ioctl(2) versus those from read(2), except in one way: By comparison of closure values. Again, such a procedure imposes complexity on clients and reduces freedom in use of the bus reset closure. So, change the ABI to suppress queuing of bus reset events before the first FW_CDEV_IOC_GET_INFO ioctl was issued by the client. Note, this ABI change cannot be version-controlled. The kernel cannot distinguish old from new clients before the first FW_CDEV_IOC_GET_INFO ioctl. We will try to back-merge this change into currently maintained stable/ longterm series, and we only document the new behaviour. The old behavior is now considered a kernel bug, which it basically is. Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de> Cc: <stable@kernel.org>
Diffstat (limited to 'drivers/firewire/core-cdev.c')
1 files changed, 10 insertions, 8 deletions
diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index 9b5915ebeb35..e6ad3bb6c1a6 100644
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -253,14 +253,11 @@ static int fw_device_op_open(struct inode *inode, struct file *file)
+ INIT_LIST_HEAD(&client->link);
file->private_data = client;
- mutex_lock(&device->client_list_mutex);
- list_add_tail(&client->link, &device->client_list);
- mutex_unlock(&device->client_list_mutex);
return nonseekable_open(inode, file);
@@ -451,15 +448,20 @@ static int ioctl_get_info(struct client *client, union ioctl_arg *arg)
if (ret != 0)
return -EFAULT;
+ mutex_lock(&client->device->client_list_mutex);
client->bus_reset_closure = a->bus_reset_closure;
if (a->bus_reset != 0) {
fill_bus_reset_event(&bus_reset, client);
- if (copy_to_user(u64_to_uptr(a->bus_reset),
- &bus_reset, sizeof(bus_reset)))
- return -EFAULT;
+ ret = copy_to_user(u64_to_uptr(a->bus_reset),
+ &bus_reset, sizeof(bus_reset));
+ if (ret == 0 && list_empty(&client->link))
+ list_add_tail(&client->link, &client->device->client_list);
- return 0;
+ mutex_unlock(&client->device->client_list_mutex);
+ return ret ? -EFAULT : 0;
static int add_client_resource(struct client *client,

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