cred: simpler, 1D supplementary groups

Current supplementary groups code can massively overallocate memory and
is implemented in a way so that access to individual gid is done via 2D
array.

If number of gids is <= 32, memory allocation is more or less tolerable
(140/148 bytes).  But if it is not, code allocates full page (!)
regardless and, what's even more fun, doesn't reuse small 32-entry
array.

2D array means dependent shifts, loads and LEAs without possibility to
optimize them (gid is never known at compile time).

All of the above is unnecessary.  Switch to the usual
trailing-zero-len-array scheme.  Memory is allocated with
kmalloc/vmalloc() and only as much as needed.  Accesses become simpler
(LEA 8(gi,idx,4) or even without displacement).

Maximum number of gids is 65536 which translates to 256KB+8 bytes.  I
think kernel can handle such allocation.

On my usual desktop system with whole 9 (nine) aux groups, struct
group_info shrinks from 148 bytes to 44 bytes, yay!

Nice side effects:

 - "gi->gid[i]" is shorter than "GROUP_AT(gi, i)", less typing,

 - fix little mess in net/ipv4/ping.c
   should have been using GROUP_AT macro but this point becomes moot,

 - aux group allocation is persistent and should be accounted as such.

Link: http://lkml.kernel.org/r/20160817201927.GA2096@p183.telecom.by
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Vasily Kulikov <segoon@openwall.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 9 insertions, 9 deletions

diff --git a/net/sunrpc/auth_generic.c b/net/sunrpc/auth_generic.c
index 1682195..83dffea 100644
--- a/net/sunrpc/auth_generic.c
+++ b/net/sunrpc/auth_generic.c
@@ -176,8 +176,8 @@ generic_match(struct auth_cred *acred, struct rpc_cred *cred, int flags)
 	if (gcred->acred.group_info->ngroups != acred->group_info->ngroups)
 		goto out_nomatch;
 	for (i = 0; i < gcred->acred.group_info->ngroups; i++) {
-		if (!gid_eq(GROUP_AT(gcred->acred.group_info, i),
-				GROUP_AT(acred->group_info, i)))
+		if (!gid_eq(gcred->acred.group_info->gid[i],
+				acred->group_info->gid[i]))
 			goto out_nomatch;
 	}
 out_match:
diff --git a/net/sunrpc/auth_gss/gss_rpc_xdr.c b/net/sunrpc/auth_gss/gss_rpc_xdr.c
index eeeba5a..dc6fb79 100644
--- a/net/sunrpc/auth_gss/gss_rpc_xdr.c
+++ b/net/sunrpc/auth_gss/gss_rpc_xdr.c
@@ -229,7 +229,7 @@ static int gssx_dec_linux_creds(struct xdr_stream *xdr,
 		kgid = make_kgid(&init_user_ns, tmp);
 		if (!gid_valid(kgid))
 			goto out_free_groups;
-		GROUP_AT(creds->cr_group_info, i) = kgid;
+		creds->cr_group_info->gid[i] = kgid;
 	}
 
 	return 0;
diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
index d858202..d67f7e1 100644
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -479,7 +479,7 @@ static int rsc_parse(struct cache_detail *cd,
 			kgid = make_kgid(&init_user_ns, id);
 			if (!gid_valid(kgid))
 				goto out;
-			GROUP_AT(rsci.cred.cr_group_info, i) = kgid;
+			rsci.cred.cr_group_info->gid[i] = kgid;
 		}
 
 		/* mech name */
diff --git a/net/sunrpc/auth_unix.c b/net/sunrpc/auth_unix.c
index a99278c..a1d768a9 100644
--- a/net/sunrpc/auth_unix.c
+++ b/net/sunrpc/auth_unix.c
@@ -79,7 +79,7 @@ unx_create_cred(struct rpc_auth *auth, struct auth_cred *acred, int flags, gfp_t
 
 	cred->uc_gid = acred->gid;
 	for (i = 0; i < groups; i++)
-		cred->uc_gids[i] = GROUP_AT(acred->group_info, i);
+		cred->uc_gids[i] = acred->group_info->gid[i];
 	if (i < NFS_NGROUPS)
 		cred->uc_gids[i] = INVALID_GID;
 
@@ -127,7 +127,7 @@ unx_match(struct auth_cred *acred, struct rpc_cred *rcred, int flags)
 	if (groups > NFS_NGROUPS)
 		groups = NFS_NGROUPS;
 	for (i = 0; i < groups ; i++)
-		if (!gid_eq(cred->uc_gids[i], GROUP_AT(acred->group_info, i)))
+		if (!gid_eq(cred->uc_gids[i], acred->group_info->gid[i]))
 			return 0;
 	if (groups < NFS_NGROUPS && gid_valid(cred->uc_gids[groups]))
 		return 0;
diff --git a/net/sunrpc/svcauth_unix.c b/net/sunrpc/svcauth_unix.c
index dfacdc9..64af4f0 100644
--- a/net/sunrpc/svcauth_unix.c
+++ b/net/sunrpc/svcauth_unix.c
@@ -517,7 +517,7 @@ static int unix_gid_parse(struct cache_detail *cd,
 		kgid = make_kgid(&init_user_ns, gid);
 		if (!gid_valid(kgid))
 			goto out;
-		GROUP_AT(ug.gi, i) = kgid;
+		ug.gi->gid[i] = kgid;
 	}
 
 	ugp = unix_gid_lookup(cd, uid);
@@ -564,7 +564,7 @@ static int unix_gid_show(struct seq_file *m,
 
 	seq_printf(m, "%u %d:", from_kuid_munged(user_ns, ug->uid), glen);
 	for (i = 0; i < glen; i++)
-		seq_printf(m, " %d", from_kgid_munged(user_ns, GROUP_AT(ug->gi, i)));
+		seq_printf(m, " %d", from_kgid_munged(user_ns, ug->gi->gid[i]));
 	seq_printf(m, "\n");
 	return 0;
 }
@@ -817,7 +817,7 @@ svcauth_unix_accept(struct svc_rqst *rqstp, __be32 *authp)
 		return SVC_CLOSE;
 	for (i = 0; i < slen; i++) {
 		kgid_t kgid = make_kgid(&init_user_ns, svc_getnl(argv));
-		GROUP_AT(cred->cr_group_info, i) = kgid;
+		cred->cr_group_info->gid[i] = kgid;
 	}
 	if (svc_getu32(argv) != htonl(RPC_AUTH_NULL) || svc_getu32(argv) != 0) {
 		*authp = rpc_autherr_badverf;