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random: vDSO: reject unknown getrandom() flags
Like the getrandom() syscall, vDSO getrandom() must also reject unknown flags. [1] It would be possible to return -EINVAL from vDSO itself, but in the possible case that a new flag is added to getrandom() syscall in the future, it would be easier to get the behavior from the syscall, instead of erroring until the vDSO is extended to support the new flag or explicitly falling back. [1] Designing the API: Planning for Extension https://docs.kernel.org/process/adding-syscalls.html#designing-the-api-planning-for-extension Signed-off-by: Yann Droneaud <yann@droneaud.fr> [Jason: reworded commit message] Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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@ -85,6 +85,10 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_
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if (unlikely(((unsigned long)opaque_state & ~PAGE_MASK) + sizeof(*state) > PAGE_SIZE))
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return -EFAULT;
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/* Handle unexpected flags by falling back to the kernel. */
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if (unlikely(flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE)))
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goto fallback_syscall;
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/* If the caller passes the wrong size, which might happen due to CRIU, fallback. */
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if (unlikely(opaque_len != sizeof(*state)))
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goto fallback_syscall;
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