A measurement is presented of the t (t) over bar production cross section (sigma(t (t) over bar)) in proton-proton collisions at a centre-of-mass energy of 7 TeV, in the all-jet final state that contains at least six jets, two of which are tagged as originating from b quarks. The data correspond to an integrated luminosity of 3.54 fb(-1), collected with the CMS detector at the LHC. The cross section is determined through an unbinned maximum likelihood fit of background and t (t) over bar signal to the reconstructed mass spectrum of t (t) over bar candidates in the data, in which events are subjected to a kinematic fit assuming a t (t) over bar -> W(+)bW(-)(b) over bar -> 6 jets hypothesis. The measurement yields sigma(t (t) over bar) = 139 +/- 10 (stat.) +/- 26 (syst.) +/- 3 (lum.) pb, a result consistent with those obtained in other t (t) over bar decay channels, as well as with predictions of the standard model.