CVE-2026-53090

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

bpf: Fix ld_{abs,ind} failure path analysis in subprogs

Usage of ld_{abs,ind} instructions got extended into subprogs some time

ago via commit 09b28d76eac4 ("bpf: Add abnormal return checks."). These

are only allowed in subprograms when the latter are BTF annotated and

have scalar return types.

The code generator in bpf_gen_ld_abs() has an abnormal exit path (r0=0 +

exit) from legacy cBPF times. While the enforcement is on scalar return

types, the verifier must also simulate the path of abnormal exit if the

packet data load via ld_{abs,ind} failed.

This is currently not the case. Fix it by having the verifier simulate

both success and failure paths, and extend it in similar ways as we do

for tail calls. The success path (r0=unknown, continue to next insn) is

pushed onto stack for later validation and the r0=0 and return to the

caller is done on the fall-through side.