mirror of https://github.com/torvalds/linux.git
cc2f39d6ac
Currently, hwrng_fill is not cleared until the hwrng_fillfn() thread
exits. Since hwrng_unregister() reads hwrng_fill outside the rng_mutex
lock, a concurrent hwrng_unregister() may call kthread_stop() again on
the same task.
Additionally, if hwrng_unregister() is called immediately after
hwrng_register(), the stopped thread may have never been executed. Thus,
hwrng_fill remains dirty even after hwrng_unregister() returns. In this
case, subsequent calls to hwrng_register() will fail to start new
threads, and hwrng_unregister() will call kthread_stop() on the same
freed task. In both cases, a use-after-free occurs:
refcount_t: addition on 0; use-after-free.
WARNING: ... at lib/refcount.c:25 refcount_warn_saturate+0xec/0x1c0
Call Trace:
kthread_stop+0x181/0x360
hwrng_unregister+0x288/0x380
virtrng_remove+0xe3/0x200
This patch fixes the race by protecting the global hwrng_fill pointer
inside the rng_mutex lock, so that hwrng_fillfn() thread is stopped only
once, and calls to kthread_run() and kthread_stop() are serialized
with the lock held.
To avoid deadlock in hwrng_fillfn() while being stopped with the lock
held, we convert current_rng to RCU, so that get_current_rng() can read
current_rng without holding the lock. To remove the lock from put_rng(),
we also delay the actual cleanup into a work_struct.
Since get_current_rng() no longer returns ERR_PTR values, the IS_ERR()
checks are removed from its callers.
With hwrng_fill protected by the rng_mutex lock, hwrng_fillfn() can no
longer clear hwrng_fill itself. Therefore, if hwrng_fillfn() returns
directly after current_rng is dropped, kthread_stop() would be called on
a freed task_struct later. To fix this, hwrng_fillfn() calls schedule()
now to keep the task alive until being stopped. The kthread_stop() call
is also moved from hwrng_unregister() to drop_current_rng(), ensuring
kthread_stop() is called on all possible paths where current_rng becomes
NULL, so that the thread would not wait forever.
Fixes:
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||
|---|---|---|
| .. | ||
| acpi | ||
| asm-generic | ||
| clocksource | ||
| crypto | ||
| cxl | ||
| drm | ||
| dt-bindings | ||
| hyperv | ||
| keys | ||
| kunit | ||
| kvm | ||
| linux | ||
| math-emu | ||
| media | ||
| memory | ||
| misc | ||
| net | ||
| pcmcia | ||
| ras | ||
| rdma | ||
| rv | ||
| scsi | ||
| soc | ||
| sound | ||
| target | ||
| trace | ||
| uapi | ||
| ufs | ||
| vdso | ||
| video | ||
| xen | ||
| Kbuild | ||