Re: [PATCH 5/5] libdiskfs: add permission check to file_chflags

[Samuel Thibault]

Justus Winter, le Mon 16 Jun 2014 19:49:29 +0200, a écrit :
> Only root is allowed to change the high 16 bits.  The TODO entry says
> otherwise, but that must be a mistake.  For reference, see the glibc
> sources, sysdeps/mach/hurd/bits/stat.h.
> 
> * libdiskfs/file-chflags.c (diskfs_S_file_chflags): Add permission
> check.
> * TODO (libdiskfs): Remove entry.

Ack.

> ---
>  TODO                     | 2 --
>  libdiskfs/file-chflags.c | 8 ++++++++
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/TODO b/TODO
> index d2500dc..0387e9f 100644
> --- a/TODO
> +++ b/TODO
> @@ -108,8 +108,6 @@ See `tasks', the exported task list.
>     Rename the rest to libhurdutil or somesuch.
>  
>  ** libdiskfs
> -*** file_chflags does not do proper permission checking (non-root isn't
> -    supposed to be able to change the low bits)
>  *** Add the short-circuited-but-not-builtin translator startup code from
>      dir-lookup to fsys_getroot.  Compare and match carefully these two
>      routines and then share common code.
> diff --git a/libdiskfs/file-chflags.c b/libdiskfs/file-chflags.c
> index 01dc495..a29ff07 100644
> --- a/libdiskfs/file-chflags.c
> +++ b/libdiskfs/file-chflags.c
> @@ -23,8 +23,15 @@ kern_return_t
>  diskfs_S_file_chflags (struct protid *cred,
>                     int flags)
>  {
> +#define HI(X)        ((X) & 0xffff0000u)
>    CHANGE_NODE_FIELD (cred,
>                  ({
> +                     /* Only root is allowed to change the high 16
> +                        bits.  */
> +                     if ((HI (flags) != HI (np->dn_stat.st_flags))
> +                         && ! idvec_contains (cred->user->uids, 0))
> +                       return EPERM;
> +
>                    err = fshelp_isowner (&np->dn_stat, cred->user);
>                    if (!err)
>                      err = diskfs_validate_flags_change (np, flags);
> @@ -37,4 +44,5 @@ diskfs_S_file_chflags (struct protid *cred,
>                      diskfs_notice_filechange(np, FILE_CHANGED_META, 
>                                               0, 0);
>                  }));
> +#undef HI
>  }
> -- 
> 2.0.0
> 

-- 
Samuel
<k> faut en profiter, aujourd'hui, les blagues bidon sont à 100 dollars
 -+- #sos-bourse -+-