If there is an upper limit on m then it is CFL. As L can be written as
L = L1 U L2 U L3 U L4 U... finite times.
L1 = { $a^n$$b^n$ | n >=1}
L2 = { $a^{2n}$$b^n$ | n >=1}
L3 = { $a^{3n}$$b^n$ | n >=1}
L4 = { $a^{4n}$$b^n$ | n >=1}
....
Finite times.
We know that finite union of CFL is CFL.