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Commit 5010e948 authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by David S. Miller
Browse files

samples/bpf: bpf_load.c detect and abort if ELF maps section size is wrong 



The struct bpf_map_def was extended in commit fb30d4b7 ("bpf: Add tests
for map-in-map") with member unsigned int inner_map_idx.  This changed the size
of the maps section in the generated ELF _kern.o files.

Unfortunately the loader in bpf_load.c does not detect or handle this.  Thus,
older _kern.o files became incompatible, and caused hard-to-debug errors
where the syscall validation rejected BPF_MAP_CREATE request.

This patch only detect the situation and aborts load_bpf_file(). It also
add code comments warning people that read this loader for inspiration
for these pitfalls.

Fixes: fb30d4b7 ("bpf: Add tests for map-in-map")
Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 39f37095

samples/bpf/bpf_load.c

+31 −9
Original line number Diff line number Diff line
@@ -185,12 +185,16 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size) 
	return 0;

}



static int load_maps(struct bpf_map_def *maps, int len,

static int load_maps(struct bpf_map_def *maps, int nr_maps,

		     const char **map_names, fixup_map_cb fixup_map)

{

	int i;



	for (i = 0; i < len / sizeof(struct bpf_map_def); i++) {

	/*

	 * Warning: Using "maps" pointing to ELF data_maps->d_buf as

	 * an array of struct bpf_map_def is a wrong assumption about

	 * the ELF maps section format.

	 */

	for (i = 0; i < nr_maps; i++) {

		if (fixup_map)

			fixup_map(&maps[i], map_names[i], i);
@@ -269,6 +273,10 @@ static int parse_relo_and_apply(Elf_Data *data, Elf_Data *symbols, 
			return 1;

		}

		insn[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;

		/*

		 * Warning: Using sizeof(struct bpf_map_def) here is a

		 * wrong assumption about ELF maps section format

		 */

		insn[insn_idx].imm = map_fd[sym.st_value / sizeof(struct bpf_map_def)];

	}
@@ -311,18 +319,18 @@ static int get_sorted_map_names(Elf *elf, Elf_Data *symbols, int maps_shndx, 
		map_name = elf_strptr(elf, strtabidx, map_symbols[i].st_name);

		if (!map_name) {

			printf("cannot get map symbol\n");

			return 1;

			return -1;

		}



		map_names[i] = strdup(map_name);

		if (!map_names[i]) {

			printf("strdup(%s): %s(%d)\n", map_name,

			       strerror(errno), errno);

			return 1;

			return -1;

		}

	}



	return 0;

	return nr_maps;

}



static int do_load_bpf_file(const char *path, fixup_map_cb fixup_map)
@@ -396,11 +404,25 @@ static int do_load_bpf_file(const char *path, fixup_map_cb fixup_map) 
	}



	if (data_maps) {

		if (get_sorted_map_names(elf, symbols, maps_shndx, strtabidx,

					 map_names))

		int nr_maps;

		int prog_elf_map_sz;



		nr_maps = get_sorted_map_names(elf, symbols, maps_shndx,

					       strtabidx, map_names);

		if (nr_maps < 0)

			goto done;



		/* Deduce map struct size stored in ELF maps section */

		prog_elf_map_sz = data_maps->d_size / nr_maps;

		if (prog_elf_map_sz != sizeof(struct bpf_map_def)) {

			printf("Error: ELF maps sec wrong size (%d/%lu),"

			       " old kern.o file?\n",

			       prog_elf_map_sz, sizeof(struct bpf_map_def));

			ret = 1;

			goto done;

		}



		if (load_maps(data_maps->d_buf, data_maps->d_size,

		if (load_maps(data_maps->d_buf, nr_maps,

			      (const char **)map_names, fixup_map))

			goto done;