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

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The struct bpf_map_def was extended in commit fb30d4b71214 ("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: fb30d4b71214 ("bpf: Add tests for map-in-map")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jesper Dangaard Brouer 2017-04-28 16:25:04 +02:00 committed by David S. Miller
parent 39f3709599
commit 5010e94842
1 changed files with 31 additions and 9 deletions
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40
samples/bpf/bpf_load.c
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@ -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;
if (load_maps(data_maps->d_buf, data_maps->d_size,
/* 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, nr_maps,
(const char **)map_names, fixup_map))
goto done;