Only allocate the space we need before calling kern_getgroups instead

of allocating what ever the user asks for up to "ngroups_max + 1".  On
systems with large values of kern.ngroups this will be more efficient.

The now redundant check that the array is large enough in
kern_getgroups() is deliberate to allow this change to be merged to
stable/8 without breaking potential third party consumers of the API.

Reported by:	bde
MFC after:	28 days

2 files changed, 14 insertions, 4 deletions

diff --git a/sys/i386/ibcs2/ibcs2_misc.c b/sys/i386/ibcs2/ibcs2_misc.c
index 6d25937..c537100 100644
--- a/sys/i386/ibcs2/ibcs2_misc.c
+++ b/sys/i386/ibcs2/ibcs2_misc.c
@@ -663,9 +663,13 @@ ibcs2_getgroups(td, uap)
 	u_int i, ngrp;
 	int error;
 
-	if (uap->gidsetsize < 0)
-		return (EINVAL);
-	ngrp = MIN(uap->gidsetsize, ngroups_max + 1);
+	if (uap->gidsetsize < td->td_ucred->cr_ngroups) {
+		if (uap->gidsetsize == 0)
+			ngrp = 0;
+		else
+			return (EINVAL);
+	} else
+		ngrp = td->td_ucred->cr_ngroups;
 	gp = malloc(ngrp * sizeof(*gp), M_TEMP, M_WAITOK);
 	error = kern_getgroups(td, &ngrp, gp);
 	if (error)
diff --git a/sys/kern/kern_prot.c b/sys/kern/kern_prot.c
index 5a5c24c..16b0f37 100644
--- a/sys/kern/kern_prot.c
+++ b/sys/kern/kern_prot.c
@@ -283,7 +283,13 @@ getgroups(struct thread *td, register struct getgroups_args *uap)
 	u_int ngrp;
 	int error;
 
-	ngrp = MIN(uap->gidsetsize, ngroups_max + 1);
+	if (uap->gidsetsize < td->td_ucred->cr_ngroups) {
+		if (uap->gidsetsize == 0)
+			ngrp = 0;
+		else
+			return (EINVAL);
+	} else
+		ngrp = td->td_ucred->cr_ngroups;
 	groups = malloc(ngrp * sizeof(*groups), M_TEMP, M_WAITOK);
 	error = kern_getgroups(td, &ngrp, groups);
 	if (error)