[PATCH v3] bpf: fix uapi bpf_prog_info fields alignment

[Baruch Siach]

Merge commit 1c8c5a9d38f60 ("Merge
git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next") undid the
fix from commit 36f9814a494 ("bpf: fix uapi hole for 32 bit compat
applications") by taking the gpl_compatible 1-bit field definition from
commit b85fab0e67b162 ("bpf: Add gpl_compatible flag to struct
bpf_prog_info") as is. That breaks architectures with 16-bit alignment
like m68k. Add 31-bit pad after gpl_compatible to restore alignment of
following fields.

Thanks to Dmitry V. Levin his analysis of this bug history.

Cc: Jiri Olsa <jo...@kernel.org>
Cc: Daniel Borkmann <dan...@iogearbox.net>
Cc: Geert Uytterhoeven <ge...@linux-m68k.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Baruch Siach <bar...@tkos.co.il>
---
v3:
Use alignment pad as Alexei Starovoitov suggested

v2:
Use anonymous union with pad to make it less likely to break again in
the future.
---
 include/uapi/linux/bpf.h       | 1 +
 tools/include/uapi/linux/bpf.h | 1 +
 2 files changed, 2 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index a8b823c30b43..29a5bc3d5c66 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3143,6 +3143,7 @@ struct bpf_prog_info {
        char name[BPF_OBJ_NAME_LEN];
        __u32 ifindex;
        __u32 gpl_compatible:1;
+       __u32 :31; /* alignment pad */
        __u64 netns_dev;
        __u64 netns_ino;
        __u32 nr_jited_ksyms;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index a8b823c30b43..29a5bc3d5c66 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3143,6 +3143,7 @@ struct bpf_prog_info {
        char name[BPF_OBJ_NAME_LEN];
        __u32 ifindex;
        __u32 gpl_compatible:1;
+       __u32 :31; /* alignment pad */
        __u64 netns_dev;
        __u64 netns_ino;
        __u32 nr_jited_ksyms;
-- 
2.20.1