Re: [PATCH v5] kernel: make groups_sort calling a responsibility group_info allocators

[David Howells]

NeilBrown  wrote:

> David: do you agree that this sort of content would be appropriate in
> that file (which you apparently authored).  Would you like to update it,
> or shall I?

Please update it.

Thanks,
David

Re: [PATCH v5] kernel: make groups_sort calling a responsibility group_info allocators

[David Howells]

NeilBrown  wrote:

> David: do you agree that this sort of content would be appropriate in
> that file (which you apparently authored).  Would you like to update it,
> or shall I?

Please update it.

Thanks,
David

Re: [PATCH v5] kernel: make groups_sort calling a responsibility group_info allocators

[NeilBrown]

On Mon, Dec 11 2017, Thiago Rafael Becker wrote:

> In testing, we found that nfsd threads may call set_groups in parallel for
> the same entry cached in auth.unix.gid, racing in the call of groups_sort,
> corrupting the groups for that entry and leading to permission denials for
> the client.
>
> This patch:
>  - Make groups_sort globally visible.
>  - Move the call to groups_sort to the modifiers of group_info
>  - Remove the call to groups_sort from set_groups
>
> Signed-off-by: Thiago Rafael Becker 

Reviewed-by: NeilBrown 

Thanks.  I like this better as a single patch.

I'd probably suggest "Cc: sta...@vger.kernel.org".
Less important bugfixes have gone to stable...

It might be nice to enhance
  Documentation/security/credentials.rst 
to explain that the groups list is always sorted, and must be sorted
before set_groups() or set_current_groups() is called, but
as the document doesn't mention any of this at all, this is purely
an extra enhancement and doesn't need to be included in the same patch.

David: do you agree that this sort of content would be appropriate in
that file (which you apparently authored).  Would you like to update it,
or shall I?

Thanks,
NeilBrown



> ---
>  arch/s390/kernel/compat_linux.c   | 1 +
>  fs/nfsd/auth.c| 3 +++
>  include/linux/cred.h  | 1 +
>  kernel/groups.c   | 5 +++--
>  kernel/uid16.c| 1 +
>  net/sunrpc/auth_gss/gss_rpc_xdr.c | 1 +
>  net/sunrpc/auth_gss/svcauth_gss.c | 1 +
>  net/sunrpc/svcauth_unix.c | 2 ++
>  8 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
> index f04db37..59eea9c 100644
> --- a/arch/s390/kernel/compat_linux.c
> +++ b/arch/s390/kernel/compat_linux.c
> @@ -263,6 +263,7 @@ COMPAT_SYSCALL_DEFINE2(s390_setgroups16, int, gidsetsize, 
> u16 __user *, grouplis
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/fs/nfsd/auth.c b/fs/nfsd/auth.c
> index 697f8ae..f650e47 100644
> --- a/fs/nfsd/auth.c
> +++ b/fs/nfsd/auth.c
> @@ -60,6 +60,9 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export 
> *exp)
>   gi->gid[i] = exp->ex_anon_gid;
>   else
>   gi->gid[i] = rqgi->gid[i];
> +
> + /* Each thread allocates its own gi, no race */
> + groups_sort(gi);
>   }
>   } else {
>   gi = get_group_info(rqgi);
> diff --git a/include/linux/cred.h b/include/linux/cred.h
> index 099058e..6312865 100644
> --- a/include/linux/cred.h
> +++ b/include/linux/cred.h
> @@ -83,6 +83,7 @@ extern int set_current_groups(struct group_info *);
>  extern void set_groups(struct cred *, struct group_info *);
>  extern int groups_search(const struct group_info *, kgid_t);
>  extern bool may_setgroups(void);
> +extern void groups_sort(struct group_info *);
>  
>  /*
>   * The security context of a task
> diff --git a/kernel/groups.c b/kernel/groups.c
> index e357bc8..daae2f2 100644
> --- a/kernel/groups.c
> +++ b/kernel/groups.c
> @@ -86,11 +86,12 @@ static int gid_cmp(const void *_a, const void *_b)
>   return gid_gt(a, b) - gid_lt(a, b);
>  }
>  
> -static void groups_sort(struct group_info *group_info)
> +void groups_sort(struct group_info *group_info)
>  {
>   sort(group_info->gid, group_info->ngroups, sizeof(*group_info->gid),
>gid_cmp, NULL);
>  }
> +EXPORT_SYMBOL(groups_sort);
>  
>  /* a simple bsearch */
>  int groups_search(const struct group_info *group_info, kgid_t grp)
> @@ -122,7 +123,6 @@ int groups_search(const struct group_info *group_info, 
> kgid_t grp)
>  void set_groups(struct cred *new, struct group_info *group_info)
>  {
>   put_group_info(new->group_info);
> - groups_sort(group_info);
>   get_group_info(group_info);
>   new->group_info = group_info;
>  }
> @@ -206,6 +206,7 @@ SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user 
> *, grouplist)
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/kernel/uid16.c b/kernel/uid16.c
> index ce74a49..ef1da2a 100644
> --- a/kernel/uid16.c
> +++ b/kernel/uid16.c
> @@ -192,6 +192,7 @@ SYSCALL_DEFINE2(setgroups16, int, gidsetsize, old_gid_t 
> __user *, grouplist)
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/net/sunrpc/auth_gss/gss_rpc_xdr.c 
> b/net/sunrpc/auth_gss/gss_rpc_xdr.c
> index c4778ca..444380f 100644
> --- a/net/sunrpc/auth_gss/gss_rpc_xdr.c
> +++ b/net/sunrpc/auth_gss/gss_rpc_xdr.c
> @@ -231,6 +231,7 @@ static int 

Re: [PATCH v5] kernel: make groups_sort calling a responsibility group_info allocators

[NeilBrown]

On Mon, Dec 11 2017, Thiago Rafael Becker wrote:

> In testing, we found that nfsd threads may call set_groups in parallel for
> the same entry cached in auth.unix.gid, racing in the call of groups_sort,
> corrupting the groups for that entry and leading to permission denials for
> the client.
>
> This patch:
>  - Make groups_sort globally visible.
>  - Move the call to groups_sort to the modifiers of group_info
>  - Remove the call to groups_sort from set_groups
>
> Signed-off-by: Thiago Rafael Becker 

Reviewed-by: NeilBrown 

Thanks.  I like this better as a single patch.

I'd probably suggest "Cc: sta...@vger.kernel.org".
Less important bugfixes have gone to stable...

It might be nice to enhance
  Documentation/security/credentials.rst 
to explain that the groups list is always sorted, and must be sorted
before set_groups() or set_current_groups() is called, but
as the document doesn't mention any of this at all, this is purely
an extra enhancement and doesn't need to be included in the same patch.

David: do you agree that this sort of content would be appropriate in
that file (which you apparently authored).  Would you like to update it,
or shall I?

Thanks,
NeilBrown



> ---
>  arch/s390/kernel/compat_linux.c   | 1 +
>  fs/nfsd/auth.c| 3 +++
>  include/linux/cred.h  | 1 +
>  kernel/groups.c   | 5 +++--
>  kernel/uid16.c| 1 +
>  net/sunrpc/auth_gss/gss_rpc_xdr.c | 1 +
>  net/sunrpc/auth_gss/svcauth_gss.c | 1 +
>  net/sunrpc/svcauth_unix.c | 2 ++
>  8 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
> index f04db37..59eea9c 100644
> --- a/arch/s390/kernel/compat_linux.c
> +++ b/arch/s390/kernel/compat_linux.c
> @@ -263,6 +263,7 @@ COMPAT_SYSCALL_DEFINE2(s390_setgroups16, int, gidsetsize, 
> u16 __user *, grouplis
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/fs/nfsd/auth.c b/fs/nfsd/auth.c
> index 697f8ae..f650e47 100644
> --- a/fs/nfsd/auth.c
> +++ b/fs/nfsd/auth.c
> @@ -60,6 +60,9 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export 
> *exp)
>   gi->gid[i] = exp->ex_anon_gid;
>   else
>   gi->gid[i] = rqgi->gid[i];
> +
> + /* Each thread allocates its own gi, no race */
> + groups_sort(gi);
>   }
>   } else {
>   gi = get_group_info(rqgi);
> diff --git a/include/linux/cred.h b/include/linux/cred.h
> index 099058e..6312865 100644
> --- a/include/linux/cred.h
> +++ b/include/linux/cred.h
> @@ -83,6 +83,7 @@ extern int set_current_groups(struct group_info *);
>  extern void set_groups(struct cred *, struct group_info *);
>  extern int groups_search(const struct group_info *, kgid_t);
>  extern bool may_setgroups(void);
> +extern void groups_sort(struct group_info *);
>  
>  /*
>   * The security context of a task
> diff --git a/kernel/groups.c b/kernel/groups.c
> index e357bc8..daae2f2 100644
> --- a/kernel/groups.c
> +++ b/kernel/groups.c
> @@ -86,11 +86,12 @@ static int gid_cmp(const void *_a, const void *_b)
>   return gid_gt(a, b) - gid_lt(a, b);
>  }
>  
> -static void groups_sort(struct group_info *group_info)
> +void groups_sort(struct group_info *group_info)
>  {
>   sort(group_info->gid, group_info->ngroups, sizeof(*group_info->gid),
>gid_cmp, NULL);
>  }
> +EXPORT_SYMBOL(groups_sort);
>  
>  /* a simple bsearch */
>  int groups_search(const struct group_info *group_info, kgid_t grp)
> @@ -122,7 +123,6 @@ int groups_search(const struct group_info *group_info, 
> kgid_t grp)
>  void set_groups(struct cred *new, struct group_info *group_info)
>  {
>   put_group_info(new->group_info);
> - groups_sort(group_info);
>   get_group_info(group_info);
>   new->group_info = group_info;
>  }
> @@ -206,6 +206,7 @@ SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user 
> *, grouplist)
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/kernel/uid16.c b/kernel/uid16.c
> index ce74a49..ef1da2a 100644
> --- a/kernel/uid16.c
> +++ b/kernel/uid16.c
> @@ -192,6 +192,7 @@ SYSCALL_DEFINE2(setgroups16, int, gidsetsize, old_gid_t 
> __user *, grouplist)
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/net/sunrpc/auth_gss/gss_rpc_xdr.c 
> b/net/sunrpc/auth_gss/gss_rpc_xdr.c
> index c4778ca..444380f 100644
> --- a/net/sunrpc/auth_gss/gss_rpc_xdr.c
> +++ b/net/sunrpc/auth_gss/gss_rpc_xdr.c
> @@ -231,6 +231,7 @@ static int gssx_dec_linux_creds(struct xdr_stream *xdr,
>

Re: [PATCH v5] kernel: make groups_sort calling a responsibility group_info allocators

[J. Bruce Fields]

ACK.  (Assuming somebody else takes it--Andrew?  Al?  Or I can take it
through the nfsd tree.  I'm not sure who owns the stuff under kernel/.)

--b.

On Mon, Dec 11, 2017 at 01:14:20PM -0200, Thiago Rafael Becker wrote:
> In testing, we found that nfsd threads may call set_groups in parallel for
> the same entry cached in auth.unix.gid, racing in the call of groups_sort,
> corrupting the groups for that entry and leading to permission denials for
> the client.
> 
> This patch:
>  - Make groups_sort globally visible.
>  - Move the call to groups_sort to the modifiers of group_info
>  - Remove the call to groups_sort from set_groups
> 
> Signed-off-by: Thiago Rafael Becker 
> ---
>  arch/s390/kernel/compat_linux.c   | 1 +
>  fs/nfsd/auth.c| 3 +++
>  include/linux/cred.h  | 1 +
>  kernel/groups.c   | 5 +++--
>  kernel/uid16.c| 1 +
>  net/sunrpc/auth_gss/gss_rpc_xdr.c | 1 +
>  net/sunrpc/auth_gss/svcauth_gss.c | 1 +
>  net/sunrpc/svcauth_unix.c | 2 ++
>  8 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
> index f04db37..59eea9c 100644
> --- a/arch/s390/kernel/compat_linux.c
> +++ b/arch/s390/kernel/compat_linux.c
> @@ -263,6 +263,7 @@ COMPAT_SYSCALL_DEFINE2(s390_setgroups16, int, gidsetsize, 
> u16 __user *, grouplis
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/fs/nfsd/auth.c b/fs/nfsd/auth.c
> index 697f8ae..f650e47 100644
> --- a/fs/nfsd/auth.c
> +++ b/fs/nfsd/auth.c
> @@ -60,6 +60,9 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export 
> *exp)
>   gi->gid[i] = exp->ex_anon_gid;
>   else
>   gi->gid[i] = rqgi->gid[i];
> +
> + /* Each thread allocates its own gi, no race */
> + groups_sort(gi);
>   }
>   } else {
>   gi = get_group_info(rqgi);
> diff --git a/include/linux/cred.h b/include/linux/cred.h
> index 099058e..6312865 100644
> --- a/include/linux/cred.h
> +++ b/include/linux/cred.h
> @@ -83,6 +83,7 @@ extern int set_current_groups(struct group_info *);
>  extern void set_groups(struct cred *, struct group_info *);
>  extern int groups_search(const struct group_info *, kgid_t);
>  extern bool may_setgroups(void);
> +extern void groups_sort(struct group_info *);
>  
>  /*
>   * The security context of a task
> diff --git a/kernel/groups.c b/kernel/groups.c
> index e357bc8..daae2f2 100644
> --- a/kernel/groups.c
> +++ b/kernel/groups.c
> @@ -86,11 +86,12 @@ static int gid_cmp(const void *_a, const void *_b)
>   return gid_gt(a, b) - gid_lt(a, b);
>  }
>  
> -static void groups_sort(struct group_info *group_info)
> +void groups_sort(struct group_info *group_info)
>  {
>   sort(group_info->gid, group_info->ngroups, sizeof(*group_info->gid),
>gid_cmp, NULL);
>  }
> +EXPORT_SYMBOL(groups_sort);
>  
>  /* a simple bsearch */
>  int groups_search(const struct group_info *group_info, kgid_t grp)
> @@ -122,7 +123,6 @@ int groups_search(const struct group_info *group_info, 
> kgid_t grp)
>  void set_groups(struct cred *new, struct group_info *group_info)
>  {
>   put_group_info(new->group_info);
> - groups_sort(group_info);
>   get_group_info(group_info);
>   new->group_info = group_info;
>  }
> @@ -206,6 +206,7 @@ SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user 
> *, grouplist)
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/kernel/uid16.c b/kernel/uid16.c
> index ce74a49..ef1da2a 100644
> --- a/kernel/uid16.c
> +++ b/kernel/uid16.c
> @@ -192,6 +192,7 @@ SYSCALL_DEFINE2(setgroups16, int, gidsetsize, old_gid_t 
> __user *, grouplist)
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/net/sunrpc/auth_gss/gss_rpc_xdr.c 
> b/net/sunrpc/auth_gss/gss_rpc_xdr.c
> index c4778ca..444380f 100644
> --- a/net/sunrpc/auth_gss/gss_rpc_xdr.c
> +++ b/net/sunrpc/auth_gss/gss_rpc_xdr.c
> @@ -231,6 +231,7 @@ static int gssx_dec_linux_creds(struct xdr_stream *xdr,
>   goto out_free_groups;
>   creds->cr_group_info->gid[i] = kgid;
>   }
> + groups_sort(creds->cr_group_info);
>  
>   return 0;
>  out_free_groups:
> diff --git a/net/sunrpc/auth_gss/svcauth_gss.c 
> b/net/sunrpc/auth_gss/svcauth_gss.c
> index 5dd4e6c..2653119 100644
> --- a/net/sunrpc/auth_gss/svcauth_gss.c
> +++ b/net/sunrpc/auth_gss/svcauth_gss.c
> @@ -481,6 +481,7 @@ static int rsc_parse(struct cache_detail *cd,
>   goto 

Re: [PATCH v5] kernel: make groups_sort calling a responsibility group_info allocators

[J. Bruce Fields]

ACK.  (Assuming somebody else takes it--Andrew?  Al?  Or I can take it
through the nfsd tree.  I'm not sure who owns the stuff under kernel/.)

--b.

On Mon, Dec 11, 2017 at 01:14:20PM -0200, Thiago Rafael Becker wrote:
> In testing, we found that nfsd threads may call set_groups in parallel for
> the same entry cached in auth.unix.gid, racing in the call of groups_sort,
> corrupting the groups for that entry and leading to permission denials for
> the client.
> 
> This patch:
>  - Make groups_sort globally visible.
>  - Move the call to groups_sort to the modifiers of group_info
>  - Remove the call to groups_sort from set_groups
> 
> Signed-off-by: Thiago Rafael Becker 
> ---
>  arch/s390/kernel/compat_linux.c   | 1 +
>  fs/nfsd/auth.c| 3 +++
>  include/linux/cred.h  | 1 +
>  kernel/groups.c   | 5 +++--
>  kernel/uid16.c| 1 +
>  net/sunrpc/auth_gss/gss_rpc_xdr.c | 1 +
>  net/sunrpc/auth_gss/svcauth_gss.c | 1 +
>  net/sunrpc/svcauth_unix.c | 2 ++
>  8 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
> index f04db37..59eea9c 100644
> --- a/arch/s390/kernel/compat_linux.c
> +++ b/arch/s390/kernel/compat_linux.c
> @@ -263,6 +263,7 @@ COMPAT_SYSCALL_DEFINE2(s390_setgroups16, int, gidsetsize, 
> u16 __user *, grouplis
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/fs/nfsd/auth.c b/fs/nfsd/auth.c
> index 697f8ae..f650e47 100644
> --- a/fs/nfsd/auth.c
> +++ b/fs/nfsd/auth.c
> @@ -60,6 +60,9 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export 
> *exp)
>   gi->gid[i] = exp->ex_anon_gid;
>   else
>   gi->gid[i] = rqgi->gid[i];
> +
> + /* Each thread allocates its own gi, no race */
> + groups_sort(gi);
>   }
>   } else {
>   gi = get_group_info(rqgi);
> diff --git a/include/linux/cred.h b/include/linux/cred.h
> index 099058e..6312865 100644
> --- a/include/linux/cred.h
> +++ b/include/linux/cred.h
> @@ -83,6 +83,7 @@ extern int set_current_groups(struct group_info *);
>  extern void set_groups(struct cred *, struct group_info *);
>  extern int groups_search(const struct group_info *, kgid_t);
>  extern bool may_setgroups(void);
> +extern void groups_sort(struct group_info *);
>  
>  /*
>   * The security context of a task
> diff --git a/kernel/groups.c b/kernel/groups.c
> index e357bc8..daae2f2 100644
> --- a/kernel/groups.c
> +++ b/kernel/groups.c
> @@ -86,11 +86,12 @@ static int gid_cmp(const void *_a, const void *_b)
>   return gid_gt(a, b) - gid_lt(a, b);
>  }
>  
> -static void groups_sort(struct group_info *group_info)
> +void groups_sort(struct group_info *group_info)
>  {
>   sort(group_info->gid, group_info->ngroups, sizeof(*group_info->gid),
>gid_cmp, NULL);
>  }
> +EXPORT_SYMBOL(groups_sort);
>  
>  /* a simple bsearch */
>  int groups_search(const struct group_info *group_info, kgid_t grp)
> @@ -122,7 +123,6 @@ int groups_search(const struct group_info *group_info, 
> kgid_t grp)
>  void set_groups(struct cred *new, struct group_info *group_info)
>  {
>   put_group_info(new->group_info);
> - groups_sort(group_info);
>   get_group_info(group_info);
>   new->group_info = group_info;
>  }
> @@ -206,6 +206,7 @@ SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user 
> *, grouplist)
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/kernel/uid16.c b/kernel/uid16.c
> index ce74a49..ef1da2a 100644
> --- a/kernel/uid16.c
> +++ b/kernel/uid16.c
> @@ -192,6 +192,7 @@ SYSCALL_DEFINE2(setgroups16, int, gidsetsize, old_gid_t 
> __user *, grouplist)
>   return retval;
>   }
>  
> + groups_sort(group_info);
>   retval = set_current_groups(group_info);
>   put_group_info(group_info);
>  
> diff --git a/net/sunrpc/auth_gss/gss_rpc_xdr.c 
> b/net/sunrpc/auth_gss/gss_rpc_xdr.c
> index c4778ca..444380f 100644
> --- a/net/sunrpc/auth_gss/gss_rpc_xdr.c
> +++ b/net/sunrpc/auth_gss/gss_rpc_xdr.c
> @@ -231,6 +231,7 @@ static int gssx_dec_linux_creds(struct xdr_stream *xdr,
>   goto out_free_groups;
>   creds->cr_group_info->gid[i] = kgid;
>   }
> + groups_sort(creds->cr_group_info);
>  
>   return 0;
>  out_free_groups:
> diff --git a/net/sunrpc/auth_gss/svcauth_gss.c 
> b/net/sunrpc/auth_gss/svcauth_gss.c
> index 5dd4e6c..2653119 100644
> --- a/net/sunrpc/auth_gss/svcauth_gss.c
> +++ b/net/sunrpc/auth_gss/svcauth_gss.c
> @@ -481,6 +481,7 @@ static int rsc_parse(struct cache_detail *cd,
>   goto out;
>   

Re: [PATCH v5] kernel: make groups_sort calling a responsibility group_info allocators

[Matthew Wilcox]

On Mon, Dec 11, 2017 at 01:14:20PM -0200, Thiago Rafael Becker wrote:
> In testing, we found that nfsd threads may call set_groups in parallel for
> the same entry cached in auth.unix.gid, racing in the call of groups_sort,
> corrupting the groups for that entry and leading to permission denials for
> the client.
> 
> This patch:
>  - Make groups_sort globally visible.
>  - Move the call to groups_sort to the modifiers of group_info
>  - Remove the call to groups_sort from set_groups
> 
> Signed-off-by: Thiago Rafael Becker 

Reviewed-by: Matthew Wilcox 

Re: [PATCH v5] kernel: make groups_sort calling a responsibility group_info allocators

[Matthew Wilcox]

On Mon, Dec 11, 2017 at 01:14:20PM -0200, Thiago Rafael Becker wrote:
> In testing, we found that nfsd threads may call set_groups in parallel for
> the same entry cached in auth.unix.gid, racing in the call of groups_sort,
> corrupting the groups for that entry and leading to permission denials for
> the client.
> 
> This patch:
>  - Make groups_sort globally visible.
>  - Move the call to groups_sort to the modifiers of group_info
>  - Remove the call to groups_sort from set_groups
> 
> Signed-off-by: Thiago Rafael Becker 

Reviewed-by: Matthew Wilcox