misc: fastrpc: Fix use-after-free and race in fastrpc_map_find

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: misc: fastrpc: Fix use-after-free and race in fastrpc_map_find Currently, there is a race window between the point when the mutex is unlocked in fastrpc_map_lookup and the reference count increasing (fastrpc_map_get) in fastrpc_map_find, which can also lead to use-after-free. So lets merge fastrpc_map_find into fastrpc_map_lookup which allows us to both protect the maps list by also taking the &fl->lock spinlock and the reference count, since the spinlock will be released only after. Add take_ref argument to make this suitable for all callers.

References

• https://git.kernel.org/stable/c/a50c5c25b6e7d2824698c0e6385f882a18f4a498
• https://git.kernel.org/stable/c/9446fa1683a7e3937d9970248ced427c1983a1c5