In the Linux kernel, the following vulnerability has been resolved: greybus: raw: fix use-after...

In the Linux kernel, the following vulnerability has been resolved:

greybus: raw: fix use-after-free if write is called after disconnect

If a user writes to the chardev after disconnect has been called, the kernel panics with the following trace (with CONFIG_INIT_ON_FREE_DEFAULT_ON=y):

    BUG: kernel NULL pointer dereference, address: 0000000000000218
     ...
    Call Trace:
     <TASK>
     gb_operation_create_common+0x61/0x180
     gb_operation_create_flags+0x28/0xa0
     gb_operation_sync_timeout+0x6f/0x100
     raw_write+0x7b/0xc7 [gb_raw]
     vfs_write+0xcf/0x420
     ? task_mm_cid_work+0x136/0x220
     ksys_write+0x63/0xe0
     do_syscall_64+0xa4/0x290
     entry_SYSCALL_64_after_hwframe+0x77/0x7f

Disconnect calls gb_connection_destroy, which ends up freeing the connection object. When gb_operation_sync is called in the write file operations, its gets a freed connection as parameter and the kernel panics.

The gb_connection_destroy cannot be moved out of the disconnect function, as the Greybus subsystem expect all connections belonging to a bundle to be destroyed when disconnect returns.

To prevent this bug, use a rw lock to synchronize access between write and disconnect. This guarantees that the write function doesn't try to use a disconnected connection.