CVE-2026-98816: bpf: Fix overflow of jump offset in constant blinding

In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix overflow of jump offset in constant blinding

bpfjitblindinsn() rewrites 'if rX op imm goto off' into:

AX = imm ^ rnd AX ^= rnd if rX op AX goto off

and subtracts 2 from off when the jump is backward. off is s16, so -32767 and -32768 wrap and the jump goes 32767 insns forward, past the end of the prog. The jump is inside the patch, hence bpfadjbranches() doesn't check it. The kernel crashes when such prog runs with bpfjitharden=2.

Return -ERANGE in such case. bpfjitblindconstants() fails the same way when blinding of other insns moves a jump out of range.