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Message-ID: <149338948065.27354.8568861008673180957.stgit@firesoul>
Date: Fri, 28 Apr 2017 16:25:04 +0200
From: Jesper Dangaard Brouer <brouer@...hat.com>
To: kafai@...com
Cc: netdev@...r.kernel.org, eric@...it.org,
Daniel Borkmann <borkmann@...earbox.net>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Jesper Dangaard Brouer <brouer@...hat.com>
Subject: [net-next PATCH V1] samples/bpf: bpf_load.c detect and abort if ELF
maps section size is wrong
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@...hat.com>
---
Is it worth to implement proper backward-compat loading of older ELF objects
with this bpf-loader?
samples/bpf/bpf_load.c | 40 +++++++++++++++++++++++++++++++---------
1 file changed, 31 insertions(+), 9 deletions(-)
diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c
index 0d449d8032d1..b84ac9dbff18 100644
--- a/samples/bpf/bpf_load.c
+++ b/samples/bpf/bpf_load.c
@@ -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;
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