Is there is any uncertainty in the measurement of the speed of light?
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See page 131 of the SI brochure:
The metre, symbol $\mathrm m$, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuum, $c$, to be $299\, 792\, 458$ when expressed in the unit $\mathrm m\mathrm s^{−1}$, where the second is defined in terms of the caesium frequency $\Delta\nu_{Cs}$.
This definition implies the exact relation $c = 299\, 792\, 458\mathrm m\mathrm s^{−1}$.
(Emphasis mine)
