diff mbox series

[net-next,v3,1/2] libbpf: parse maps sections of varying size

Message ID 20171005144158.14860-2-kraigatgoog@gmail.com
State Accepted, archived
Delegated to: David Miller
Headers show
Series libbpf: support more map options | expand

Commit Message

Craig Gallek Oct. 5, 2017, 2:41 p.m. UTC 
From: Craig Gallek <kraig@google.com>

This library previously assumed a fixed-size map options structure.
Any new options were ignored.  In order to allow the options structure
to grow and to support parsing older programs, this patch updates
the maps section parsing to handle varying sizes.

Object files with maps sections smaller than expected will have the new
fields initialized to zero.  Object files which have larger than expected
maps sections will be rejected unless all of the unrecognized data is zero.

This change still assumes that each map definition in the maps section
is the same size.

Signed-off-by: Craig Gallek <kraig@google.com>
---
 tools/lib/bpf/libbpf.c | 70 +++++++++++++++++++++++++++++---------------------
 1 file changed, 41 insertions(+), 29 deletions(-)

Comments

Jesper Dangaard Brouer Oct. 5, 2017, 5:52 p.m. UTC | #1 
On Thu,  5 Oct 2017 10:41:57 -0400 Craig Gallek <kraigatgoog@gmail.com> wrote:

> From: Craig Gallek <kraig@google.com>
> 
> This library previously assumed a fixed-size map options structure.
> Any new options were ignored.  In order to allow the options structure
> to grow and to support parsing older programs, this patch updates
> the maps section parsing to handle varying sizes.
> 
> Object files with maps sections smaller than expected will have the new
> fields initialized to zero.  Object files which have larger than expected
> maps sections will be rejected unless all of the unrecognized data is zero.
> 
> This change still assumes that each map definition in the maps section
> is the same size.
> 
> Signed-off-by: Craig Gallek <kraig@google.com>
> ---
>  tools/lib/bpf/libbpf.c | 70 +++++++++++++++++++++++++++++---------------------
>  1 file changed, 41 insertions(+), 29 deletions(-)

Thank you for working on this! :-)

Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Daniel Borkmann Oct. 5, 2017, 7:25 p.m. UTC | #2 
On 10/05/2017 04:41 PM, Craig Gallek wrote:
> From: Craig Gallek <kraig@google.com>
>
> This library previously assumed a fixed-size map options structure.
> Any new options were ignored.  In order to allow the options structure
> to grow and to support parsing older programs, this patch updates
> the maps section parsing to handle varying sizes.
>
> Object files with maps sections smaller than expected will have the new
> fields initialized to zero.  Object files which have larger than expected
> maps sections will be rejected unless all of the unrecognized data is zero.
>
> This change still assumes that each map definition in the maps section
> is the same size.
>
> Signed-off-by: Craig Gallek <kraig@google.com>

Thanks,

Acked-by: Daniel Borkmann <daniel@iogearbox.net>
diff mbox series

Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 4f402dcdf372..23152890ec60 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -579,31 +579,6 @@  bpf_object__init_kversion(struct bpf_object *obj,
 	return 0;
 }
 
-static int
-bpf_object__validate_maps(struct bpf_object *obj)
-{
-	int i;
-
-	/*
-	 * If there's only 1 map, the only error case should have been
-	 * catched in bpf_object__init_maps().
-	 */
-	if (!obj->maps || !obj->nr_maps || (obj->nr_maps == 1))
-		return 0;
-
-	for (i = 1; i < obj->nr_maps; i++) {
-		const struct bpf_map *a = &obj->maps[i - 1];
-		const struct bpf_map *b = &obj->maps[i];
-
-		if (b->offset - a->offset < sizeof(struct bpf_map_def)) {
-			pr_warning("corrupted map section in %s: map \"%s\" too small\n",
-				   obj->path, a->name);
-			return -EINVAL;
-		}
-	}
-	return 0;
-}
-
 static int compare_bpf_map(const void *_a, const void *_b)
 {
 	const struct bpf_map *a = _a;
@@ -615,7 +590,7 @@  static int compare_bpf_map(const void *_a, const void *_b)
 static int
 bpf_object__init_maps(struct bpf_object *obj)
 {
-	int i, map_idx, nr_maps = 0;
+	int i, map_idx, map_def_sz, nr_maps = 0;
 	Elf_Scn *scn;
 	Elf_Data *data;
 	Elf_Data *symbols = obj->efile.symbols;
@@ -658,6 +633,15 @@  bpf_object__init_maps(struct bpf_object *obj)
 	if (!nr_maps)
 		return 0;
 
+	/* Assume equally sized map definitions */
+	map_def_sz = data->d_size / nr_maps;
+	if (!data->d_size || (data->d_size % nr_maps) != 0) {
+		pr_warning("unable to determine map definition size "
+			   "section %s, %d maps in %zd bytes\n",
+			   obj->path, nr_maps, data->d_size);
+		return -EINVAL;
+	}
+
 	obj->maps = calloc(nr_maps, sizeof(obj->maps[0]));
 	if (!obj->maps) {
 		pr_warning("alloc maps for object failed\n");
@@ -690,7 +674,7 @@  bpf_object__init_maps(struct bpf_object *obj)
 				      obj->efile.strtabidx,
 				      sym.st_name);
 		obj->maps[map_idx].offset = sym.st_value;
-		if (sym.st_value + sizeof(struct bpf_map_def) > data->d_size) {
+		if (sym.st_value + map_def_sz > data->d_size) {
 			pr_warning("corrupted maps section in %s: last map \"%s\" too small\n",
 				   obj->path, map_name);
 			return -EINVAL;
@@ -704,12 +688,40 @@  bpf_object__init_maps(struct bpf_object *obj)
 		pr_debug("map %d is \"%s\"\n", map_idx,
 			 obj->maps[map_idx].name);
 		def = (struct bpf_map_def *)(data->d_buf + sym.st_value);
-		obj->maps[map_idx].def = *def;
+		/*
+		 * If the definition of the map in the object file fits in
+		 * bpf_map_def, copy it.  Any extra fields in our version
+		 * of bpf_map_def will default to zero as a result of the
+		 * calloc above.
+		 */
+		if (map_def_sz <= sizeof(struct bpf_map_def)) {
+			memcpy(&obj->maps[map_idx].def, def, map_def_sz);
+		} else {
+			/*
+			 * Here the map structure being read is bigger than what
+			 * we expect, truncate if the excess bits are all zero.
+			 * If they are not zero, reject this map as
+			 * incompatible.
+			 */
+			char *b;
+			for (b = ((char *)def) + sizeof(struct bpf_map_def);
+			     b < ((char *)def) + map_def_sz; b++) {
+				if (*b != 0) {
+					pr_warning("maps section in %s: \"%s\" "
+						   "has unrecognized, non-zero "
+						   "options\n",
+						   obj->path, map_name);
+					return -EINVAL;
+				}
+			}
+			memcpy(&obj->maps[map_idx].def, def,
+			       sizeof(struct bpf_map_def));
+		}
 		map_idx++;
 	}
 
 	qsort(obj->maps, obj->nr_maps, sizeof(obj->maps[0]), compare_bpf_map);
-	return bpf_object__validate_maps(obj);
+	return 0;
 }
 
 static int bpf_object__elf_collect(struct bpf_object *obj)