Messages in this thread | | | Date | Mon, 14 Nov 2022 10:07:02 -0800 | From | Dmitry Torokhov <> | Subject | Re: [syzbot] KASAN: use-after-free Read in kernfs_next_descendant_post (2) |
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On Mon, Nov 14, 2022 at 09:34:16AM -0800, Luis Chamberlain wrote: > On Mon, Oct 31, 2022 at 12:53:00PM -1000, Tejun Heo wrote: > > (cc'ing Luis for firmware loader and quoting the whole body) > > > > On Sat, Oct 22, 2022 at 06:52:28AM +0800, Hillf Danton wrote: > > > On 20 Oct 2022 00:15:40 -0700 > > > > syzbot has found a reproducer for the following issue on: > > > > > > > > HEAD commit: 55be6084c8e0 Merge tag 'timers-core-2022-10-05' of git://g.. > > > > git tree: upstream > > > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1449d53c880000 > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=df75278aabf0681a > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=6bc35f3913193fe7f0d3 > > > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14e01c72880000 > > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1128908c880000 > > > > > > See if the change to ueagle driver alone can survive syzbot test. > > > > > > #syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git aae703b02f92 > > > > > > --- a/include/linux/netdevice.h > > > +++ b/include/linux/netdevice.h > > > @@ -3663,8 +3663,9 @@ static inline bool netif_attr_test_online(unsigned long j, > > > static inline unsigned int netif_attrmask_next(int n, const unsigned long *srcp, > > > unsigned int nr_bits) > > > { > > > - /* n is a prior cpu */ > > > - cpu_max_bits_warn(n + 1, nr_bits); > > > + /* -1 is a legal arg here. */ > > > + if (n != -1) > > > + cpu_max_bits_warn(n, nr_bits); > > > > > > if (srcp) > > > return find_next_bit(srcp, nr_bits, n + 1); > > > @@ -3685,8 +3686,9 @@ static inline int netif_attrmask_next_and(int n, const unsigned long *src1p, > > > const unsigned long *src2p, > > > unsigned int nr_bits) > > > { > > > - /* n is a prior cpu */ > > > - cpu_max_bits_warn(n + 1, nr_bits); > > > + /* -1 is a legal arg here. */ > > > + if (n != -1) > > > + cpu_max_bits_warn(n, nr_bits); > > > > > > if (src1p && src2p) > > > return find_next_and_bit(src1p, src2p, nr_bits, n + 1); > > > --- a/drivers/usb/atm/ueagle-atm.c > > > +++ b/drivers/usb/atm/ueagle-atm.c > > > @@ -597,9 +597,8 @@ static int uea_send_modem_cmd(struct usb > > > } > > > > > > static void uea_upload_pre_firmware(const struct firmware *fw_entry, > > > - void *context) > > > + struct usb_device *usb) > > > { > > > - struct usb_device *usb = context; > > > const u8 *pfw; > > > u8 value; > > > u32 crc = 0; > > > @@ -679,6 +678,7 @@ static int uea_load_firmware(struct usb_ > > > { > > > int ret; > > > char *fw_name = EAGLE_FIRMWARE; > > > + const struct firmware *fw; > > > > > > uea_enters(usb); > > > uea_info(usb, "pre-firmware device, uploading firmware\n"); > > > @@ -701,13 +701,13 @@ static int uea_load_firmware(struct usb_ > > > break; > > > } > > > > > > - ret = request_firmware_nowait(THIS_MODULE, 1, fw_name, &usb->dev, > > > - GFP_KERNEL, usb, > > > - uea_upload_pre_firmware); > > > + ret = request_firmware(&fw, fw_name, &usb->dev); > > > if (ret) > > > uea_err(usb, "firmware %s is not available\n", fw_name); > > > - else > > > + else { > > > uea_info(usb, "loading firmware %s\n", fw_name); > > > + uea_upload_pre_firmware(fw, usb); > > > + } > > > > > > uea_leaves(usb); > > > return ret; > > > > So, the problem is that while request_firmware_nowait() inc's the ref on the > > device, if the device gets removed later, having a ref isn't sufficient for > > adding stuff to the device. A relatively easy solution would be putting > > these firmware load work items into its own workqueue and flushing it on > > device removal path. Luis, what do you think? > > Since we *can* remove a device after we get a module reference and > since fw_cache_is_setup() tries to use the device before get_device() > (even though this is not the issue reported), I think perhaps the fix > below may be generic and best.
I do not see how moving the point where we acquire device refcount around fixes anything. Caller of request_firmware_nowait() is supposed to have a valid reference to device object and it is supposed to stay valid for the entire duration of request_firmware_nowait(). Grabbing and extra reference only matters if the device (or other refcounted structure) is being passed to another thread of execution.
I think what Tejun is saying is the only way to fix this. Similarly to work struct, where users are supposed to call cancel_work_sync() during teardown, users of request_firmware_nowait() need to wait for it to complete before continuing with tearing down the instance. See for example ims-pcu driver where it tries to request firmware asynchronously when it finds the device in bootloader mode, and is waiting for it completion when handling device disconnect:
https://elixir.bootlin.com/linux/v6.1-rc3/source/drivers/input/misc/ims-pcu.c#L1978
Thanks.
-- Dmitry
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