Re: [PATCH] virtiofsd: Seccomp: Add 'send' for syslog

[Dr. David Alan Gilbert]

* Daniel P. Berrangé (berrange@redhat.com) wrote:
> On Mon, Nov 02, 2020 at 03:07:50PM +0000, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > On ppc it looks like syslog ends up using 'send' rather than 'sendto'.
> > 
> > Reference: https://github.com/kata-containers/kata-containers/issues/1050
> > 
> > Reported-by: amulmek1@in.ibm.com
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> >  tools/virtiofsd/passthrough_seccomp.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/tools/virtiofsd/passthrough_seccomp.c 
> > b/tools/virtiofsd/passthrough_seccomp.c
> > index eb9af8265f..672fb72a31 100644
> > --- a/tools/virtiofsd/passthrough_seccomp.c
> > +++ b/tools/virtiofsd/passthrough_seccomp.c
> > @@ -118,6 +118,7 @@ static const int syscall_whitelist[] = {
> >  
> >  /* Syscalls used when --syslog is enabled */
> >  static const int syscall_whitelist_syslog[] = {
> > +    SCMP_SYS(send),
> >      SCMP_SYS(sendto),
> >  };
> 
> With glibc, syslog() calls __send() which for Linux target is implemented
> as:
> 
> 
> ssize_t
> __libc_send (int fd, const void *buf, size_t len, int flags)
> {
> #ifdef __ASSUME_SEND_SYSCALL
>   return SYSCALL_CANCEL (send, fd, buf, len, flags);
> #elif defined __ASSUME_SENDTO_SYSCALL
>   return SYSCALL_CANCEL (sendto, fd, buf, len, flags, NULL, 0);
> #else
>   return SOCKETCALL_CANCEL (send, fd, buf, len, flags);
> #endif
> }
> 
> We can see those defines being referenced vary per architecture:
> 
> $ git grep -E '__ASSUME_SEND(TO)?_SYSCALL' sysdeps/
> sysdeps/unix/sysv/linux/alpha/kernel-features.h:#define __ASSUME_SEND_SYSCALL 
>   1
> sysdeps/unix/sysv/linux/arm/kernel-features.h:#define __ASSUME_SEND_SYSCALL   
>   1
> sysdeps/unix/sysv/linux/hppa/kernel-features.h:#define __ASSUME_SEND_SYSCALL  
>   1
> sysdeps/unix/sysv/linux/i386/kernel-features.h:# undef __ASSUME_SENDTO_SYSCALL
> sysdeps/unix/sysv/linux/ia64/kernel-features.h:#define __ASSUME_SEND_SYSCALL  
>           1
> sysdeps/unix/sysv/linux/kernel-features.h:#define __ASSUME_SENDTO_SYSCALL     
>           1
> sysdeps/unix/sysv/linux/m68k/kernel-features.h:# undef __ASSUME_SENDTO_SYSCALL
> sysdeps/unix/sysv/linux/microblaze/kernel-features.h:#define 
> __ASSUME_SEND_SYSCALL              1
> sysdeps/unix/sysv/linux/mips/kernel-features.h:# define __ASSUME_SEND_SYSCALL 
>           1
> sysdeps/unix/sysv/linux/powerpc/kernel-features.h:#define 
> __ASSUME_SEND_SYSCALL         1
> sysdeps/unix/sysv/linux/s390/kernel-features.h:# undef __ASSUME_SENDTO_SYSCALL
> sysdeps/unix/sysv/linux/send.c:#ifdef __ASSUME_SEND_SYSCALL
> sysdeps/unix/sysv/linux/send.c:#elif defined __ASSUME_SENDTO_SYSCALL
> sysdeps/unix/sysv/linux/sendto.c:#ifdef __ASSUME_SENDTO_SYSCALL
> sysdeps/unix/sysv/linux/sh/kernel-features.h:#define __ASSUME_SEND_SYSCALL    
>           1
> sysdeps/unix/sysv/linux/sparc/kernel-features.h:# undef 
> __ASSUME_SENDTO_SYSCALL
> 
> 
> So the patch is correct, but the commit message could be updated becase
> this isn't specific to PPC.  Any platform except x86, s490, m68k will
> use send() rather than sendto() based on what I see here.
> 
> With any commit message update, you can add
> 
> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

Thanks, changed to:

  On ppc, and some other archs, it looks like syslog ends up using 'send'
  rather than 'sendto'.

Dave

> 
> 
> Regards,
> Daniel
> -- 
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> 
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK