In the Linux kernel, the following vulnerability has been resolved: bpf: backtrack_insn():...

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

bpf: backtrack_insn(): Handle ld_{abs,ind} subprog exit edge

Nicholas Carlini reported a bug in precision backtracking mechanism for BPF_LD | BPF_{IND,ABS} instructions. These instructions are modelled as two branches:

• fallthrough;
• implicit exit from current subprogram.

The implicit exit case was not handled by the backtrack_insn() function. When backtracking such a path backtrack_insn() did not call bt_subprog_enter(), which meant that backtracking continued manipulating precision marks in a caller frame, while looking at instructions in a callee frame.

This lead to segmentation faults during verification (see the selftest), or unsound state pruning.