From: Jesper Dangaard Brouer brouer@redhat.com
commit edbca120a8cdfa5a5793707e33497aa5185875ca upstream.
In the days of using bpf_load.c the order in which the 'maps' sections were defines in BPF side (*_kern.c) file, were used by userspace side to identify the map via using the map order as an index. In effect the order-index is created based on the order the maps sections are stored in the ELF-object file, by the LLVM compiler.
This have also carried over in libbpf via API bpf_map__next(NULL, obj) to extract maps in the order libbpf parsed the ELF-object file.
When BTF based maps were introduced a new section type ".maps" were created. I found that the LLVM compiler doesn't create the ".maps" sections in the order they are defined in the C-file. The order in the ELF file is based on the order the map pointer is referenced in the code.
This combination of changes lead to xdp_rxq_info mixing up the map file-descriptors in userspace, resulting in very broken behaviour, but without warning the user.
This patch fix issue by instead using bpf_object__find_map_by_name() to find maps via their names. (Note, this is the ELF name, which can be longer than the name the kernel retains).
Fixes: be5bca44aa6b ("samples: bpf: convert some XDP samples from bpf_load to libbpf") Fixes: 451d1dc886b5 ("samples: bpf: update map definition to new syntax BTF-defined map") Signed-off-by: Jesper Dangaard Brouer brouer@redhat.com Signed-off-by: Alexei Starovoitov ast@kernel.org Acked-by: Toke Høiland-Jørgensen toke@redhat.com Acked-by: Andrii Nakryiko andriin@fb.com Link: https://lore.kernel.org/bpf/157529025128.29832.5953245340679936909.stgit@fir... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- samples/bpf/xdp_rxq_info_user.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/samples/bpf/xdp_rxq_info_user.c +++ b/samples/bpf/xdp_rxq_info_user.c @@ -489,9 +489,9 @@ int main(int argc, char **argv) if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd)) return EXIT_FAIL;
- map = bpf_map__next(NULL, obj); - stats_global_map = bpf_map__next(map, obj); - rx_queue_index_map = bpf_map__next(stats_global_map, obj); + map = bpf_object__find_map_by_name(obj, "config_map"); + stats_global_map = bpf_object__find_map_by_name(obj, "stats_global_map"); + rx_queue_index_map = bpf_object__find_map_by_name(obj, "rx_queue_index_map"); if (!map || !stats_global_map || !rx_queue_index_map) { printf("finding a map in obj file failed\n"); return EXIT_FAIL;