[PATCH bpf] bpf: fix uapi hole for 32 bit compat applications

[PATCH bpf] bpf: fix uapi hole for 32 bit compat applications

[Daniel Borkmann]

In 64 bit, we have a 4 byte hole between ifindex and netns_dev in the
case of struct bpf_map_info but also struct bpf_prog_info. In net-next
commit b85fab0e67b ("bpf: Add gpl_compatible flag to struct bpf_prog_info")
added a bitfield into it to expose some flags related to programs. Thus,
add an unnamed __u32 bitfield for both so that alignment keeps the same
in both 32 and 64 bit cases, and can be naturally extended from there
as in b85fab0e67b.

Before:

  # file test.o
  test.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped
  # pahole test.o
  struct bpf_map_info {
	__u32                      type;                 /*     0     4 */
	__u32                      id;                   /*     4     4 */
	__u32                      key_size;             /*     8     4 */
	__u32                      value_size;           /*    12     4 */
	__u32                      max_entries;          /*    16     4 */
	__u32                      map_flags;            /*    20     4 */
	char                       name[16];             /*    24    16 */
	__u32                      ifindex;              /*    40     4 */
	__u64                      netns_dev;            /*    44     8 */
	__u64                      netns_ino;            /*    52     8 */

	/* size: 64, cachelines: 1, members: 10 */
	/* padding: 4 */
  };

After (same as on 64 bit):

  # file test.o
  test.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped
  # pahole test.o
  struct bpf_map_info {
	__u32                      type;                 /*     0     4 */
	__u32                      id;                   /*     4     4 */
	__u32                      key_size;             /*     8     4 */
	__u32                      value_size;           /*    12     4 */
	__u32                      max_entries;          /*    16     4 */
	__u32                      map_flags;            /*    20     4 */
	char                       name[16];             /*    24    16 */
	__u32                      ifindex;              /*    40     4 */

	/* XXX 4 bytes hole, try to pack */

	__u64                      netns_dev;            /*    48     8 */
	__u64                      netns_ino;            /*    56     8 */
	/* --- cacheline 1 boundary (64 bytes) --- */

	/* size: 64, cachelines: 1, members: 10 */
	/* sum members: 60, holes: 1, sum holes: 4 */
  };

Reported-by: Dmitry V. Levin <ldv@altlinux.org>
Reported-by: Eugene Syromiatnikov <esyr@redhat.com>
Fixes: 52775b33bb507 ("bpf: offload: report device information about offloaded maps")
Fixes: 675fc275a3a2d ("bpf: offload: report device information for offloaded programs")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
 include/uapi/linux/bpf.h       | 2 ++
 tools/include/uapi/linux/bpf.h | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c5ec897..8c31773 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1017,6 +1017,7 @@ struct bpf_prog_info {
 	__aligned_u64 map_ids;
 	char name[BPF_OBJ_NAME_LEN];
 	__u32 ifindex;
+	__u32 :32;
 	__u64 netns_dev;
 	__u64 netns_ino;
 } __attribute__((aligned(8)));
@@ -1030,6 +1031,7 @@ struct bpf_map_info {
 	__u32 map_flags;
 	char  name[BPF_OBJ_NAME_LEN];
 	__u32 ifindex;
+	__u32 :32;
 	__u64 netns_dev;
 	__u64 netns_ino;
 } __attribute__((aligned(8)));
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c5ec897..8c31773 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1017,6 +1017,7 @@ struct bpf_prog_info {
 	__aligned_u64 map_ids;
 	char name[BPF_OBJ_NAME_LEN];
 	__u32 ifindex;
+	__u32 :32;
 	__u64 netns_dev;
 	__u64 netns_ino;
 } __attribute__((aligned(8)));
@@ -1030,6 +1031,7 @@ struct bpf_map_info {
 	__u32 map_flags;
 	char  name[BPF_OBJ_NAME_LEN];
 	__u32 ifindex;
+	__u32 :32;
 	__u64 netns_dev;
 	__u64 netns_ino;
 } __attribute__((aligned(8)));
-- 
2.9.5

Re: [PATCH bpf] bpf: fix uapi hole for 32 bit compat applications

[Alexei Starovoitov]

On Sat, Jun 02, 2018 at 05:21:59AM +0200, Daniel Borkmann wrote:
> In 64 bit, we have a 4 byte hole between ifindex and netns_dev in the
> case of struct bpf_map_info but also struct bpf_prog_info. In net-next
> commit b85fab0e67b ("bpf: Add gpl_compatible flag to struct bpf_prog_info")
> added a bitfield into it to expose some flags related to programs. Thus,
> add an unnamed __u32 bitfield for both so that alignment keeps the same
> in both 32 and 64 bit cases, and can be naturally extended from there
> as in b85fab0e67b.
> 
> 
> Reported-by: Dmitry V. Levin <ldv@altlinux.org>
> Reported-by: Eugene Syromiatnikov <esyr@redhat.com>
> Fixes: 52775b33bb507 ("bpf: offload: report device information about offloaded maps")
> Fixes: 675fc275a3a2d ("bpf: offload: report device information for offloaded programs")
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Acked-by: Alexei Starovoitov <ast@kernel.org>

Applied, Thanks.