[PATCH 3.16 114/254] kernel: make groups_sort calling a responsibility group_info allocators

[Ben Hutchings]

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Thiago Rafael Becker <thiago.becker@xxxxxxxxx>

commit bdcf0a423ea1c40bbb40e7ee483b50fc8aa3d758 upstream.

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

Link: http://lkml.kernel.org/r/20171211151420.18655-1-thiago.becker@xxxxxxxxx
Signed-off-by: Thiago Rafael Becker <thiago.becker@xxxxxxxxx>
Reviewed-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Reviewed-by: NeilBrown <neilb@xxxxxxxx>
Acked-by: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 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(-)

--- a/arch/s390/kernel/compat_linux.c
+++ b/arch/s390/kernel/compat_linux.c
@@ -263,6 +263,7 @@ COMPAT_SYSCALL_DEFINE2(s390_setgroups16,
 		return retval;
 	}
 
+	groups_sort(group_info);
 	retval = set_current_groups(group_info);
 	put_group_info(group_info);
 
--- a/fs/nfsd/auth.c
+++ b/fs/nfsd/auth.c
@@ -59,6 +59,9 @@ int nfsd_setuser(struct svc_rqst *rqstp,
 				GROUP_AT(gi, i) = exp->ex_anon_gid;
 			else
 				GROUP_AT(gi, i) = GROUP_AT(rqgi, i);
+
+			/* Each thread allocates its own gi, no race */
+			groups_sort(gi);
 		}
 	} else {
 		gi = get_group_info(rqgi);
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -69,6 +69,7 @@ extern int set_current_groups(struct gro
 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 *);
 
 /* access the groups "array" with this macro */
 #define GROUP_AT(gi, i) \
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -104,7 +104,7 @@ static int groups_from_user(struct group
 }
 
 /* a simple Shell sort */
-static void groups_sort(struct group_info *group_info)
+void groups_sort(struct group_info *group_info)
 {
 	int base, max, stride;
 	int gidsetsize = group_info->ngroups;
@@ -131,6 +131,7 @@ static void groups_sort(struct group_inf
 		stride /= 3;
 	}
 }
+EXPORT_SYMBOL(groups_sort);
 
 /* a simple bsearch */
 int groups_search(const struct group_info *group_info, kgid_t grp)
@@ -162,7 +163,6 @@ int groups_search(const struct group_inf
 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;
 }
@@ -246,6 +246,7 @@ SYSCALL_DEFINE2(setgroups, int, gidsetsi
 		return retval;
 	}
 
+	groups_sort(group_info);
 	retval = set_current_groups(group_info);
 	put_group_info(group_info);
 
--- a/kernel/uid16.c
+++ b/kernel/uid16.c
@@ -190,6 +190,7 @@ SYSCALL_DEFINE2(setgroups16, int, gidset
 		return retval;
 	}
 
+	groups_sort(group_info);
 	retval = set_current_groups(group_info);
 	put_group_info(group_info);
 
--- 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 x
 			goto out_free_groups;
 		GROUP_AT(creds->cr_group_info, i) = kgid;
 	}
+	groups_sort(creds->cr_group_info);
 
 	return 0;
 out_free_groups:
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -479,6 +479,7 @@ static int rsc_parse(struct cache_detail
 				goto out;
 			GROUP_AT(rsci.cred.cr_group_info, i) = kgid;
 		}
+		groups_sort(rsci.cred.cr_group_info);
 
 		/* mech name */
 		len = qword_get(&mesg, buf, mlen);
--- a/net/sunrpc/svcauth_unix.c
+++ b/net/sunrpc/svcauth_unix.c
@@ -520,6 +520,7 @@ static int unix_gid_parse(struct cache_d
 		GROUP_AT(ug.gi, i) = kgid;
 	}
 
+	groups_sort(ug.gi);
 	ugp = unix_gid_lookup(cd, uid);
 	if (ugp) {
 		struct cache_head *ch;
@@ -827,6 +828,7 @@ svcauth_unix_accept(struct svc_rqst *rqs
 		kgid_t kgid = make_kgid(&init_user_ns, svc_getnl(argv));
 		GROUP_AT(cred->cr_group_info, 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;