bpftool: Explicit errno handling in skeletons

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.

Fixes: f97b8b9bd630 ("bpftool: Fix a bug in subskeleton code generation")
Signed-off-by: Delyan Kratunov <delyank@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/3b6bfbb770c79ae64d8de26c1c1bd9d53a4b85f8.camel@fb.com

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 91af2850b505742906b0f2bd24b851abf5de8988..7678af364793f2f209597e9fdd54499679b62524 100644 (file)
--- 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\