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

["J. Bruce Fields" <bfields@fieldses.org>]

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 <thiago.becker@gmail.com>
> ---
>  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;
>  			rsci.cred.cr_group_info->gid[i] = kgid;
>  		}
> +		groups_sort(rsci.cred.cr_group_info);
>  
>  		/* mech name */
>  		len = qword_get(&mesg, buf, mlen);
> diff --git a/net/sunrpc/svcauth_unix.c b/net/sunrpc/svcauth_unix.c
> index 740b67d..af7f28f 100644
> --- a/net/sunrpc/svcauth_unix.c
> +++ b/net/sunrpc/svcauth_unix.c
> @@ -520,6 +520,7 @@ static int unix_gid_parse(struct cache_detail *cd,
>  		ug.gi->gid[i] = kgid;
>  	}
>  
> +	groups_sort(ug.gi);
>  	ugp = unix_gid_lookup(cd, uid);
>  	if (ugp) {
>  		struct cache_head *ch;
> @@ -819,6 +820,7 @@ svcauth_unix_accept(struct svc_rqst *rqstp, __be32 *authp)
>  		kgid_t kgid = make_kgid(&init_user_ns, svc_getnl(argv));
>  		cred->cr_group_info->gid[i] = kgid;
>  	}
> +	groups_sort(cred->cr_group_info);
>  	if (svc_getu32(argv) != htonl(RPC_AUTH_NULL) || svc_getu32(argv) != 0) {
>  		*authp = rpc_autherr_badverf;
>  		return SVC_DENIED;
> -- 
> 2.9.5
> 
> --
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