Subject: Re: [PATCH bpf 1/2] bpf: fix alignment of netns_dev/netns_ino fields in bpf_{map,prog}_info

From: "Dmitry V. Levin" <[email-masked]>
Date: Fri, 1 Jun 2018 06:12:10 +0300

Hi,

Looks like the ABI bug in bpf_map_info and bpf_prog info introduced
in 4.16 is going to slip into 4.17, causing extra pain to 32-bit
userspace.  I'm adding Linus to this thread in hope it might help
to get a fix applied before 4.17 is released.

On Wed, May 30, 2018 at 09:18:58PM +0300, Dmitry V. Levin wrote:
> On Sun, May 27, 2018 at 01:28:42PM +0200, Eugene Syromiatnikov wrote:
> > Recent introduction of netns_dev/netns_ino to bpf_map_info/bpf_prog info
> > has broken compat, as offsets of these fields are different in 32-bit
> > and 64-bit ABIs.  One fix (other than implementing compat support in
> > syscall in order to handle this discrepancy) is to use __aligned_u64
> > instead of __u64 for these fields.
> > 
> > Reported-by: Dmitry V. Levin <[email-masked]>
> > Fixes: 52775b33bb507 ("bpf: offload: report device information about
> > offloaded maps")
> > Fixes: 675fc275a3a2d ("bpf: offload: report device information for
> > offloaded programs")
> > 
> > Signed-off-by: Eugene Syromiatnikov <[email-masked]>
> 
> Reviewed-by: "Dmitry V. Levin" <[email-masked]>
> Cc: <[email-masked]> # v4.16+
> 
> Thanks,
> 
> > ---
> >  include/uapi/linux/bpf.h       | 8 ++++----
> >  tools/include/uapi/linux/bpf.h | 8 ++++----
> >  2 files changed, 8 insertions(+), 8 deletions(-)
> > 
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index c5ec897..903010a 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -1017,8 +1017,8 @@ struct bpf_prog_info {
> >  	__aligned_u64 map_ids;
> >  	char name[BPF_OBJ_NAME_LEN];
> >  	__u32 ifindex;
> > -	__u64 netns_dev;
> > -	__u64 netns_ino;
> > +	__aligned_u64 netns_dev;
> > +	__aligned_u64 netns_ino;
> >  } __attribute__((aligned(8)));
> >  
> >  struct bpf_map_info {
> > @@ -1030,8 +1030,8 @@ struct bpf_map_info {
> >  	__u32 map_flags;
> >  	char  name[BPF_OBJ_NAME_LEN];
> >  	__u32 ifindex;
> > -	__u64 netns_dev;
> > -	__u64 netns_ino;
> > +	__aligned_u64 netns_dev;
> > +	__aligned_u64 netns_ino;
> >  } __attribute__((aligned(8)));
> >  
> >  /* User bpf_sock_addr struct to access socket fields and sockaddr struct passed
> > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> > index c5ec897..903010a 100644
> > --- a/tools/include/uapi/linux/bpf.h
> > +++ b/tools/include/uapi/linux/bpf.h
> > @@ -1017,8 +1017,8 @@ struct bpf_prog_info {
> >  	__aligned_u64 map_ids;
> >  	char name[BPF_OBJ_NAME_LEN];
> >  	__u32 ifindex;
> > -	__u64 netns_dev;
> > -	__u64 netns_ino;
> > +	__aligned_u64 netns_dev;
> > +	__aligned_u64 netns_ino;
> >  } __attribute__((aligned(8)));
> >  
> >  struct bpf_map_info {
> > @@ -1030,8 +1030,8 @@ struct bpf_map_info {
> >  	__u32 map_flags;
> >  	char  name[BPF_OBJ_NAME_LEN];
> >  	__u32 ifindex;
> > -	__u64 netns_dev;
> > -	__u64 netns_ino;
> > +	__aligned_u64 netns_dev;
> > +	__aligned_u64 netns_ino;
> >  } __attribute__((aligned(8)));
> >  
> >  /* User bpf_sock_addr struct to access socket fields and sockaddr struct passed

-- 
ldv