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Previously, one-element and zero-length arrays were treated as true flexible arrays, even though they are actually "fake" flex arrays. The __randomize_layout would leave them untouched at the end of the struct, similarly to proper C99 flex-array members. However, this approach changed with commit1ee60356c2("gcc-plugins: randstruct: Only warn about true flexible arrays"). Now, only C99 flexible-array members will remain untouched at the end of the struct, while one-element and zero-length arrays will be subject to randomization. Fix a `__randomize_layout` crash in `struct neighbour` by transforming zero-length array `primary_key` into a proper C99 flexible-array member. Fixes:1ee60356c2("gcc-plugins: randstruct: Only warn about true flexible arrays") Closes: https://lore.kernel.org/linux-hardening/20231124102458.GB1503258@e124191.cambridge.arm.com/ Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> Reviewed-by: Kees Cook <keescook@chromium.org> Tested-by: Joey Gouly <joey.gouly@arm.com> Link: https://lore.kernel.org/r/ZWJoRsJGnCPdJ3+2@work Signed-off-by: Paolo Abeni <pabeni@redhat.com>