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Date:      Wed, 22 Oct 2014 01:09:07 +0000 (UTC)
From:      Mateusz Guzik <mjg@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r273444 - head/sys/kern
Message-ID:  <201410220109.s9M197wU009521@svn.freebsd.org>
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Author: mjg
Date: Wed Oct 22 01:09:07 2014
New Revision: 273444
URL: https://svnweb.freebsd.org/changeset/base/273444

Log:
  Avoid crdup when possible in kern_accessat.
  
  While here tidy up a little.

Modified:
  head/sys/kern/vfs_syscalls.c

Modified: head/sys/kern/vfs_syscalls.c
==============================================================================
--- head/sys/kern/vfs_syscalls.c	Wed Oct 22 01:04:16 2014	(r273443)
+++ head/sys/kern/vfs_syscalls.c	Wed Oct 22 01:09:07 2014	(r273444)
@@ -2064,7 +2064,7 @@ int
 kern_accessat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
     int flag, int amode)
 {
-	struct ucred *cred, *tmpcred;
+	struct ucred *cred, *usecred;
 	struct vnode *vp;
 	struct nameidata nd;
 	cap_rights_t rights;
@@ -2075,31 +2075,33 @@ kern_accessat(struct thread *td, int fd,
 
 	/*
 	 * Create and modify a temporary credential instead of one that
-	 * is potentially shared.
+	 * is potentially shared (if we need one).
 	 */
-	if (!(flag & AT_EACCESS)) {
-		cred = td->td_ucred;
-		tmpcred = crdup(cred);
-		tmpcred->cr_uid = cred->cr_ruid;
-		tmpcred->cr_groups[0] = cred->cr_rgid;
-		td->td_ucred = tmpcred;
+	cred = td->td_ucred;
+	if ((flag & AT_EACCESS) == 0 &&
+	    ((cred->cr_uid != cred->cr_ruid ||
+	    cred->cr_rgid != cred->cr_groups[0]))) {
+		usecred = crdup(cred);
+		usecred->cr_uid = cred->cr_ruid;
+		usecred->cr_groups[0] = cred->cr_rgid;
+		td->td_ucred = usecred;
 	} else
-		cred = tmpcred = td->td_ucred;
+		usecred = cred;
 	AUDIT_ARG_VALUE(amode);
 	NDINIT_ATRIGHTS(&nd, LOOKUP, FOLLOW | LOCKSHARED | LOCKLEAF |
 	    AUDITVNODE1, pathseg, path, fd, cap_rights_init(&rights, CAP_FSTAT),
 	    td);
 	if ((error = namei(&nd)) != 0)
-		goto out1;
+		goto out;
 	vp = nd.ni_vp;
 
-	error = vn_access(vp, amode, tmpcred, td);
+	error = vn_access(vp, amode, usecred, td);
 	NDFREE(&nd, NDF_ONLY_PNBUF);
 	vput(vp);
-out1:
-	if (!(flag & AT_EACCESS)) {
+out:
+	if (usecred != cred) {
 		td->td_ucred = cred;
-		crfree(tmpcred);
+		crfree(usecred);
 	}
 	return (error);
 }

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