libbpf: Fix double-free when linker processes empty sections
Double-free error in bpf_linker__free() was reported by James Hilliard. The error is caused by miss-use of realloc() in extend_sec(). The error occurs when two files with empty sections of the same name are linked: - when first file is processed: - extend_sec() calls realloc(dst->raw_data, dst_align_sz) with dst->raw_data == NULL and dst_align_sz == 0; - dst->raw_data is set to a special pointer to a memory block of size zero; - when second file is processed: - extend_sec() calls realloc(dst->raw_data, dst_align_sz) with dst->raw_data == <special pointer> and dst_align_sz == 0; - realloc() "frees" dst->raw_data special pointer and returns NULL; - extend_sec() exits with -ENOMEM, and the old dst->raw_data value is preserved (it is now invalid); - eventually, bpf_linker__free() attempts to free dst->raw_data again. This patch fixes the bug by avoiding -ENOMEM exit for dst_align_sz == 0. The fix was suggested by Andrii Nakryiko <andrii.nakryiko@gmail.com>. Reported-by:James Hilliard <james.hilliard1@gmail.com> Signed-off-by:
Eduard Zingerman <eddyz87@gmail.com> Signed-off-by:
Andrii Nakryiko <andrii@kernel.org> Tested-by:
James Hilliard <james.hilliard1@gmail.com> Link: https://lore.kernel.org/bpf/CADvTj4o7ZWUikKwNTwFq0O_AaX+46t_+Ca9gvWMYdWdRtTGeHQ@mail.gmail.com/ Link: https://lore.kernel.org/bpf/20230328004738.381898-3-eddyz87@gmail.com
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