[PATCH bpf-next] bpftool: explicit errno handling in skeletons

[PATCH bpf-next] bpftool: explicit errno handling in skeletons

[Delyan Kratunov]

Andrii noticed that since f97b8b9bd630 (bpftool: Fix a bug in subskeleton code generation)
the subskeleton code allows bpf_object__destroy_subskeleton to overwrite
the errno that subskeleton__open would return with. While this is not
currently an issue, let's make it future-proof.

This patch explicitly tracks err in subskeleton__open and skeleton__create
(i.e. calloc failure is explicitly ENOMEM) and ensures that errno
is -err on the error return path. The skeleton code had to be changed
since maps and progs codegen is shared with subskeletons.

Signed-off-by: Delyan Kratunov <delyank@fb.com>
---
 tools/bpf/bpftool/gen.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 7ba7ff55d2ea..e30f7bd48a2b 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -828,8 +828,10 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped)
 			s->map_cnt = %zu;			    \n\
 			s->map_skel_sz = sizeof(*s->maps);	    \n\
 			s->maps = (struct bpf_map_skeleton *)calloc(s->map_cnt, s->map_skel_sz);\n\
-			if (!s->maps)				    \n\
+			if (!s->maps) {				    \n\
+				err = -ENOMEM;			    \n\
 				goto err;			    \n\
+			}					    \n\
 		",
 		map_cnt
 	);
@@ -870,8 +872,10 @@ codegen_progs_skeleton(struct bpf_object *obj, size_t prog_cnt, bool populate_li
 			s->prog_cnt = %zu;			    \n\
 			s->prog_skel_sz = sizeof(*s->progs);	    \n\
 			s->progs = (struct bpf_prog_skeleton *)calloc(s->prog_cnt, s->prog_skel_sz);\n\
-			if (!s->progs)				    \n\
+			if (!s->progs) {			    \n\
+				err = -ENOMEM;			    \n\
 				goto err;			    \n\
+			}					    \n\
 		",
 		prog_cnt
 	);
@@ -1182,10 +1186,13 @@ static int do_skeleton(int argc, char **argv)
 		%1$s__create_skeleton(struct %1$s *obj)			    \n\
 		{							    \n\
 			struct bpf_object_skeleton *s;			    \n\
+			int err;					    \n\
 									    \n\
 			s = (struct bpf_object_skeleton *)calloc(1, sizeof(*s));\n\
-			if (!s)						    \n\
+			if (!s)	 {					    \n\
+				err = -ENOMEM;				    \n\
 				goto err;				    \n\
+			}						    \n\
 									    \n\
 			s->sz = sizeof(*s);				    \n\
 			s->name = \"%1$s\";				    \n\
@@ -1206,7 +1213,7 @@ static int do_skeleton(int argc, char **argv)
 			return 0;					    \n\
 		err:							    \n\
 			bpf_object__destroy_skeleton(s);		    \n\
-			return -ENOMEM;					    \n\
+			return err;					    \n\
 		}							    \n\
 									    \n\
 		static inline const void *%2$s__elf_bytes(size_t *sz)	    \n\
@@ -1466,12 +1473,12 @@ static int do_subskeleton(int argc, char **argv)
 									    \n\
 			obj = (struct %1$s *)calloc(1, sizeof(*obj));	    \n\
 			if (!obj) {					    \n\
-				errno = ENOMEM;				    \n\
+				err = -ENOMEM;				    \n\
 				goto err;				    \n\
 			}						    \n\
 			s = (struct bpf_object_subskeleton *)calloc(1, sizeof(*s));\n\
 			if (!s) {					    \n\
-				errno = ENOMEM;				    \n\
+				err = -ENOMEM;				    \n\
 				goto err;				    \n\
 			}						    \n\
 			s->sz = sizeof(*s);				    \n\
@@ -1483,7 +1490,7 @@ static int do_subskeleton(int argc, char **argv)
 			s->var_cnt = %2$d;				    \n\
 			s->vars = (struct bpf_var_skeleton *)calloc(%2$d, sizeof(*s->vars));\n\
 			if (!s->vars) {					    \n\
-				errno = ENOMEM;				    \n\
+				err = -ENOMEM;				    \n\
 				goto err;				    \n\
 			}						    \n\
 		",
@@ -1538,6 +1545,7 @@ static int do_subskeleton(int argc, char **argv)
 			return obj;					    \n\
 		err:							    \n\
 			%1$s__destroy(obj);				    \n\
+			errno = -err;					    \n\
 			return NULL;					    \n\
 		}							    \n\
 									    \n\
-- 
2.34.1

Re: [PATCH bpf-next] bpftool: explicit errno handling in skeletons

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Mon, 21 Mar 2022 23:29:18 +0000 you wrote:
> Andrii noticed that since f97b8b9bd630 (bpftool: Fix a bug in subskeleton code generation)
> the subskeleton code allows bpf_object__destroy_subskeleton to overwrite
> the errno that subskeleton__open would return with. While this is not
> currently an issue, let's make it future-proof.
> 
> This patch explicitly tracks err in subskeleton__open and skeleton__create
> (i.e. calloc failure is explicitly ENOMEM) and ensures that errno
> is -err on the error return path. The skeleton code had to be changed
> since maps and progs codegen is shared with subskeletons.
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpftool: explicit errno handling in skeletons
    https://git.kernel.org/bpf/bpf/c/522574fd7864

You are awesome, thank you!
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