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>

14 files changed, 46 insertions, 85 deletions

diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
index 437e611592790b..0f9cd90c11af61 100644
--- a/arch/s390/kernel/compat_linux.c
+++ b/arch/s390/kernel/compat_linux.c
@@ -189,7 +189,7 @@ static int groups16_to_user(u16 __user *grouplist, struct group_info *group_info
 	kgid_t kgid;
 
 	for (i = 0; i < group_info->ngroups; i++) {
-		kgid = GROUP_AT(group_info, i);
+		kgid = group_info->gid[i];
 		group = (u16)from_kgid_munged(user_ns, kgid);
 		if (put_user(group, grouplist+i))
 			return -EFAULT;
@@ -213,7 +213,7 @@ static int groups16_from_user(struct group_info *group_info, u16 __user *groupli
 		if (!gid_valid(kgid))
 			return -EINVAL;
 
-		GROUP_AT(group_info, i) = kgid;
+		group_info->gid[i] = kgid;
 	}
 
 	return 0;
diff --git a/drivers/staging/lustre/lustre/ptlrpc/sec.c b/drivers/staging/lustre/lustre/ptlrpc/sec.c
index 5d3995d5c69af9..a7416cd9ac7177 100644
--- a/drivers/staging/lustre/lustre/ptlrpc/sec.c
+++ b/drivers/staging/lustre/lustre/ptlrpc/sec.c
@@ -2220,7 +2220,7 @@ int sptlrpc_pack_user_desc(struct lustre_msg *msg, int offset)
 	task_lock(current);
 	if (pud->pud_ngroups > current_ngroups)
 		pud->pud_ngroups = current_ngroups;
-	memcpy(pud->pud_groups, current_cred()->group_info->blocks[0],
+	memcpy(pud->pud_groups, current_cred()->group_info->gid,
 	       pud->pud_ngroups * sizeof(__u32));
 	task_unlock(current);
 
diff --git a/fs/nfsd/auth.c b/fs/nfsd/auth.c
index 9d46a0bdd9f9ae..62469c60be2326 100644
--- a/fs/nfsd/auth.c
+++ b/fs/nfsd/auth.c
@@ -55,10 +55,10 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
 			goto oom;
 
 		for (i = 0; i < rqgi->ngroups; i++) {
-			if (gid_eq(GLOBAL_ROOT_GID, GROUP_AT(rqgi, i)))
-				GROUP_AT(gi, i) = exp->ex_anon_gid;
+			if (gid_eq(GLOBAL_ROOT_GID, rqgi->gid[i]))
+				gi->gid[i] = exp->ex_anon_gid;
 			else
-				GROUP_AT(gi, i) = GROUP_AT(rqgi, i);
+				gi->gid[i] = rqgi->gid[i];
 		}
 	} else {
 		gi = get_group_info(rqgi);
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index a204d7e109d4d6..39bfaba9c99c93 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1903,7 +1903,7 @@ static bool groups_equal(struct group_info *g1, struct group_info *g2)
 	if (g1->ngroups != g2->ngroups)
 		return false;
 	for (i=0; i<g1->ngroups; i++)
-		if (!gid_eq(GROUP_AT(g1, i), GROUP_AT(g2, i)))
+		if (!gid_eq(g1->gid[i], g2->gid[i]))
 			return false;
 	return true;
 }
diff --git a/fs/proc/array.c b/fs/proc/array.c
index d25b44601b30e2..89600fd5963d46 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -207,7 +207,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 	group_info = cred->group_info;
 	for (g = 0; g < group_info->ngroups; g++)
 		seq_put_decimal_ull(m, g ? " " : "",
-				    from_kgid_munged(user_ns, GROUP_AT(group_info, g)));
+				from_kgid_munged(user_ns, group_info->gid[g]));
 	put_cred(cred);
 	/* Trailing space shouldn't have been added in the first place. */
 	seq_putc(m, ' ');
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 257db64562e540..f0e70a1bb3acfe 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -26,15 +26,10 @@ struct inode;
 /*
  * COW Supplementary groups list
  */
-#define NGROUPS_SMALL		32
-#define NGROUPS_PER_BLOCK	((unsigned int)(PAGE_SIZE / sizeof(kgid_t)))
-
 struct group_info {
 	atomic_t	usage;
 	int		ngroups;
-	int		nblocks;
-	kgid_t		small_block[NGROUPS_SMALL];
-	kgid_t		*blocks[0];
+	kgid_t		gid[0];
 };
 
 /**
@@ -88,10 +83,6 @@ extern void set_groups(struct cred *, struct group_info *);
 extern int groups_search(const struct group_info *, kgid_t);
 extern bool may_setgroups(void);
 
-/* access the groups "array" with this macro */
-#define GROUP_AT(gi, i) \
-	((gi)->blocks[(i) / NGROUPS_PER_BLOCK][(i) % NGROUPS_PER_BLOCK])
-
 /*
  * The security context of a task
  *
diff --git a/kernel/groups.c b/kernel/groups.c
index 74d431d2525150..2fcadd66a8fd7c 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -7,55 +7,31 @@
 #include <linux/security.h>
 #include <linux/syscalls.h>
 #include <linux/user_namespace.h>
+#include <linux/vmalloc.h>
 #include <asm/uaccess.h>
 
 struct group_info *groups_alloc(int gidsetsize)
 {
-	struct group_info *group_info;
-	int nblocks;
-	int i;
-
-	nblocks = (gidsetsize + NGROUPS_PER_BLOCK - 1) / NGROUPS_PER_BLOCK;
-	/* Make sure we always allocate at least one indirect block pointer */
-	nblocks = nblocks ? : 1;
-	group_info = kmalloc(sizeof(*group_info) + nblocks*sizeof(gid_t *), GFP_USER);
-	if (!group_info)
+	struct group_info *gi;
+	unsigned int len;
+
+	len = sizeof(struct group_info) + sizeof(kgid_t) * gidsetsize;
+	gi = kmalloc(len, GFP_KERNEL_ACCOUNT|__GFP_NOWARN|__GFP_NORETRY);
+	if (!gi)
+		gi = __vmalloc(len, GFP_KERNEL_ACCOUNT|__GFP_HIGHMEM, PAGE_KERNEL);
+	if (!gi)
 		return NULL;
-	group_info->ngroups = gidsetsize;
-	group_info->nblocks = nblocks;
-	atomic_set(&group_info->usage, 1);
-
-	if (gidsetsize <= NGROUPS_SMALL)
-		group_info->blocks[0] = group_info->small_block;
-	else {
-		for (i = 0; i < nblocks; i++) {
-			kgid_t *b;
-			b = (void *)__get_free_page(GFP_USER);
-			if (!b)
-				goto out_undo_partial_alloc;
-			group_info->blocks[i] = b;
-		}
-	}
-	return group_info;
 
-out_undo_partial_alloc:
-	while (--i >= 0) {
-		free_page((unsigned long)group_info->blocks[i]);
-	}
-	kfree(group_info);
-	return NULL;
+	atomic_set(&gi->usage, 1);
+	gi->ngroups = gidsetsize;
+	return gi;
 }
 
 EXPORT_SYMBOL(groups_alloc);
 
 void groups_free(struct group_info *group_info)
 {
-	if (group_info->blocks[0] != group_info->small_block) {
-		int i;
-		for (i = 0; i < group_info->nblocks; i++)
-			free_page((unsigned long)group_info->blocks[i]);
-	}
-	kfree(group_info);
+	kvfree(group_info);
 }
 
 EXPORT_SYMBOL(groups_free);
@@ -70,7 +46,7 @@ static int groups_to_user(gid_t __user *grouplist,
 
 	for (i = 0; i < count; i++) {
 		gid_t gid;
-		gid = from_kgid_munged(user_ns, GROUP_AT(group_info, i));
+		gid = from_kgid_munged(user_ns, group_info->gid[i]);
 		if (put_user(gid, grouplist+i))
 			return -EFAULT;
 	}
@@ -95,7 +71,7 @@ static int groups_from_user(struct group_info *group_info,
 		if (!gid_valid(kgid))
 			return -EINVAL;
 
-		GROUP_AT(group_info, i) = kgid;
+		group_info->gid[i] = kgid;
 	}
 	return 0;
 }
@@ -115,15 +91,14 @@ static void groups_sort(struct group_info *group_info)
 		for (base = 0; base < max; base++) {
 			int left = base;
 			int right = left + stride;
-			kgid_t tmp = GROUP_AT(group_info, right);
+			kgid_t tmp = group_info->gid[right];
 
-			while (left >= 0 && gid_gt(GROUP_AT(group_info, left), tmp)) {
-				GROUP_AT(group_info, right) =
-				    GROUP_AT(group_info, left);
+			while (left >= 0 && gid_gt(group_info->gid[left], tmp)) {
+				group_info->gid[right] = group_info->gid[left];
 				right = left;
 				left -= stride;
 			}
-			GROUP_AT(group_info, right) = tmp;
+			group_info->gid[right] = tmp;
 		}
 		stride /= 3;
 	}
@@ -141,9 +116,9 @@ int groups_search(const struct group_info *group_info, kgid_t grp)
 	right = group_info->ngroups;
 	while (left < right) {
 		unsigned int mid = (left+right)/2;
-		if (gid_gt(grp, GROUP_AT(group_info, mid)))
+		if (gid_gt(grp, group_info->gid[mid]))
 			left = mid + 1;
-		else if (gid_lt(grp, GROUP_AT(group_info, mid)))
+		else if (gid_lt(grp, group_info->gid[mid]))
 			right = mid;
 		else
 			return 1;
diff --git a/kernel/uid16.c b/kernel/uid16.c
index d58cc4d8f0d1fa..cc40793464e3ca 100644
--- a/kernel/uid16.c
+++ b/kernel/uid16.c
@@ -117,7 +117,7 @@ static int groups16_to_user(old_gid_t __user *grouplist,
 	kgid_t kgid;
 
 	for (i = 0; i < group_info->ngroups; i++) {
-		kgid = GROUP_AT(group_info, i);
+		kgid = group_info->gid[i];
 		group = high2lowgid(from_kgid_munged(user_ns, kgid));
 		if (put_user(group, grouplist+i))
 			return -EFAULT;
@@ -142,7 +142,7 @@ static int groups16_from_user(struct group_info *group_info,
 		if (!gid_valid(kgid))
 			return -EINVAL;
 
-		GROUP_AT(group_info, i) = kgid;
+		group_info->gid[i] = kgid;
 	}
 
 	return 0;
diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 66ddcb60519a16..7cf7d6e380c2c8 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -258,7 +258,7 @@ int ping_init_sock(struct sock *sk)
 	struct net *net = sock_net(sk);
 	kgid_t group = current_egid();
 	struct group_info *group_info;
-	int i, j, count;
+	int i;
 	kgid_t low, high;
 	int ret = 0;
 
@@ -270,16 +270,11 @@ int ping_init_sock(struct sock *sk)
 		return 0;
 
 	group_info = get_current_groups();
-	count = group_info->ngroups;
-	for (i = 0; i < group_info->nblocks; i++) {
-		int cp_count = min_t(int, NGROUPS_PER_BLOCK, count);
-		for (j = 0; j < cp_count; j++) {
-			kgid_t gid = group_info->blocks[i][j];
-			if (gid_lte(low, gid) && gid_lte(gid, high))
-				goto out_release_group;
-		}
+	for (i = 0; i < group_info->ngroups; i++) {
+		kgid_t gid = group_info->gid[i];
 
-		count -= cp_count;
+		if (gid_lte(low, gid) && gid_lte(gid, high))
+			goto out_release_group;
 	}
 
 	ret = -EACCES;
diff --git a/net/sunrpc/auth_generic.c b/net/sunrpc/auth_generic.c
index 168219535a3410..83dffeadf20acb 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 eeeba5adee6d93..dc6fb79a361f1c 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 d8582028b34600..d67f7e1bc82ddc 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 a99278c984e82a..a1d768a973f529 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 dfacdc95b3f520..64af4f034de693 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;