Messages in this thread | | | Date | Tue, 31 Oct 2023 08:39:48 +0100 | From | Greg KH <> | Subject | Re: [PATCH] Devcoredump: fix use-after-free issue when releasing devcd device |
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On Tue, Oct 31, 2023 at 03:15:12PM +0800, Yu Wang wrote: > > > On 10/27/2023 7:12 PM, Greg KH wrote: > > On Thu, Oct 26, 2023 at 10:55:21PM -0700, Yu Wang wrote: > >> With sample code as below, it may hit use-after-free issue when > >> releasing devcd device. > >> > >> struct my_coredump_state { > >> struct completion dump_done; > >> ... > >> }; > >> > >> static void my_coredump_free(void *data) > >> { > >> struct my_coredump_state *dump_state = data; > >> ... > >> complete(&dump_state->dump_done); > >> } > >> > >> static void my_dev_release(struct device *dev) > >> { > >> kfree(dev); > >> } > >> > >> static void my_coredump() > >> { > >> struct my_coredump_state dump_state; > >> struct device *new_device = > >> kzalloc(sizeof(*new_device), GFP_KERNEL); > >> > >> ... > >> new_device->release = my_dev_release; > >> device_initialize(new_device); > >> ... > >> device_add(new_device); > >> ... > >> init_completion(&dump_state.dump_done); > >> dev_coredumpm(new_device, NULL, &dump_state, datalen, GFP_KERNEL, > >> my_coredump_read, my_coredump_free); > >> wait_for_completion(&dump_state.dump_done); > >> device_del(new_device); > >> put_device(new_device); > >> } > >> > >> In devcoredump framework, devcd_dev_release() will be called when > >> releasing the devcd device, it will call the free() callback first > >> and try to delete the symlink in sysfs directory of the failing device. > >> Eventhough it has checked 'devcd->failing_dev->kobj.sd' before that, > >> there is no mechanism to ensure it's still available when accessing > >> it in kernfs_find_ns(), refer to the diagram as below: > >> > >> Thread A was waiting for 'dump_state.dump_done' at #A-1-2 after > >> calling dev_coredumpm(). > >> When thread B calling devcd->free() at #B-2-1, it wakes up > >> thread A from point #A-1-2, which will call device_del() to > >> delete the device. > >> If #B-2-2 comes before #A-3-1, but #B-4 comes after #A-4, it > >> will hit use-after-free issue when trying to access > >> 'devcd->failing_dev->kobj.sd'. > >> > >> #A-1-1: dev_coredumpm() > >> #A-1-2: wait_for_completion(&dump_state.dump_done) > >> #A-1-3: device_del() > >> #A-2: kobject_del() > >> #A-3-1: sysfs_remove_dir() --> set kobj->sd=NULL > >> #A-3-2: kernfs_put() > >> #A-4: kmem_cache_free() --> free kobj->sd > >> > >> #B-1: devcd_dev_release() > >> #B-2-1: devcd->free(devcd->data) > >> #B-2-2: check devcd->failing_dev->kobj.sd > >> #B-2-3: sysfs_delete_link() > >> #B-3: kernfs_remove_by_name_ns() > >> #B-4: kernfs_find_ns() --> access devcd->failing_dev->kobj.sd > >> > >> To fix this issue, put operations on devcd->failing_dev before > >> calling the free() callback in devcd_dev_release(). > >> > >> Signed-off-by: Yu Wang <quic_yyuwang@quicinc.com> > >> --- > >> drivers/base/devcoredump.c | 5 ++--- > >> 1 file changed, 2 insertions(+), 3 deletions(-) > > > > Also, what commit id does this fix? > > Thanks for your comment :) > Do you mean the commit which introduced this issue? It's from initial version of devcoredump.c.
Ok, but then what in-kernel code has the above pattern to cause this "problem"? Why not fix that up?
thanks,
greg k-h
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