  A measurement is presented of the t t-bar cross section (sigma[ttbar]) 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 inverse femtobarns, collected with the CMS detector at the LHC. The cross
section is determined through an unbinned maximum likelihood fit of background
and t t-bar signal to the reconstructed mass spectrum of t t-bar candidates in
the data, in which events are subjected to a kinematic fit assuming a t t-bar
to W+ b W- b-bar to 6 jets hypothesis. The measurement yields sigma[ttbar] =
139 +/- 10 (stat.) +/- 26 (syst.) +/- 3 (lum.) pb, a result consistent with
those obtained in other t t-bar decay channels, as well as with predictions of
the standard model.
