Commit 81243eac authored by Alexey Dobriyan's avatar Alexey Dobriyan Committed by Linus Torvalds
Browse files

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: default avatarAlexey Dobriyan <adobriyan@gmail.com>
Cc: Vasily Kulikov <segoon@openwall.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 954f74bf

arch/s390/kernel/compat_linux.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

drivers/staging/lustre/lustre/ptlrpc/sec.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

fs/nfsd/auth.c

+3 −3
Original line number Diff line number Diff line
@@ -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);

fs/nfsd/nfs4state.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

}

fs/proc/array.c

+1 −1
Original line number Diff line number Diff line
@@ -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, ' ');

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