From d177f49f6f47414bf8ecd07d6fb4714eb24384f9 Mon Sep 17 00:00:00 2001
From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Thu, 9 Jul 2015 16:32:58 +0000
Subject: [PATCH] vfs: simplify error handling in namei

The logic is reorganised so that there is one exit point prior to the
lookup loop. This is an intermediate step to making audit logging
functions use found vnode instead of translating ni_dirfd on their own.

ni_startdir validation is removed. The only in-tree consumer is nfs
which already makes sure it is a directory.

Reviewed by:	kib
---
 sys/kern/vfs_lookup.c | 49 ++++++++++++++++++-------------------------
 1 file changed, 20 insertions(+), 29 deletions(-)

diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
index e434464e4447..a93314e88e6c 100644
--- a/sys/kern/vfs_lookup.c
+++ b/sys/kern/vfs_lookup.c
@@ -158,7 +158,7 @@ namei(struct nameidata *ndp)
 	struct vnode *dp;	/* the directory we are searching */
 	struct iovec aiov;		/* uio for reading symbolic links */
 	struct uio auio;
-	int error, linklen;
+	int error, linklen, startdir_used;
 	struct componentname *cnp = &ndp->ni_cnd;
 	struct thread *td = cnp->cn_thread;
 	struct proc *p = td->td_proc;
@@ -169,6 +169,8 @@ namei(struct nameidata *ndp)
 	    ("namei: nameiop contaminated with flags"));
 	KASSERT((cnp->cn_flags & OPMASK) == 0,
 	    ("namei: flags contaminated with nameiops"));
+	MPASS(ndp->ni_startdir == NULL || ndp->ni_startdir->v_type == VDIR ||
+	    ndp->ni_startdir->v_type == VBAD);
 	if (!lookup_shared)
 		cnp->cn_flags &= ~LOCKSHARED;
 	fdp = p->p_fd;
@@ -242,23 +244,19 @@ namei(struct nameidata *ndp)
 	if (cnp->cn_flags & AUDITVNODE2)
 		AUDIT_ARG_UPATH2(td, ndp->ni_dirfd, cnp->cn_pnbuf);
 
+	startdir_used = 0;
 	dp = NULL;
 	cnp->cn_nameptr = cnp->cn_pnbuf;
 	if (cnp->cn_pnbuf[0] == '/') {
 		error = namei_handle_root(ndp, &dp);
-		FILEDESC_SUNLOCK(fdp);
-		if (error != 0) {
-			vrele(ndp->ni_rootdir);
-			if (ndp->ni_startdir != NULL)
-				vrele(ndp->ni_startdir);
-			namei_cleanup_cnp(cnp);
-			return (error);
-		}
 	} else {
 		if (ndp->ni_startdir != NULL) {
 			dp = ndp->ni_startdir;
-			error = 0;
-		} else if (ndp->ni_dirfd != AT_FDCWD) {
+			startdir_used = 1;
+		} else if (ndp->ni_dirfd == AT_FDCWD) {
+			dp = fdp->fd_cdir;
+			VREF(dp);
+		} else {
 			cap_rights_t rights;
 
 			rights = ndp->ni_rightsneeded;
@@ -285,25 +283,18 @@ namei(struct nameidata *ndp)
 			}
 #endif
 		}
-		if (error != 0 || dp != NULL) {
-			FILEDESC_SUNLOCK(fdp);
-			if (error == 0 && dp->v_type != VDIR) {
-				vrele(dp);
-				error = ENOTDIR;
-			}
-		}
-		if (error) {
-			vrele(ndp->ni_rootdir);
-			namei_cleanup_cnp(cnp);
-			return (error);
-		}
+		if (error == 0 && dp->v_type != VDIR)
+			error = ENOTDIR;
 	}
-	if (dp == NULL) {
-		dp = fdp->fd_cdir;
-		VREF(dp);
-		FILEDESC_SUNLOCK(fdp);
-		if (ndp->ni_startdir != NULL)
-			vrele(ndp->ni_startdir);
+	FILEDESC_SUNLOCK(fdp);
+	if (ndp->ni_startdir != NULL && !startdir_used)
+		vrele(ndp->ni_startdir);
+	if (error != 0) {
+		if (dp != NULL)
+			vrele(dp);
+		vrele(ndp->ni_rootdir);
+		namei_cleanup_cnp(cnp);
+		return (error);
 	}
 	SDT_PROBE(vfs, namei, lookup, entry, dp, cnp->cn_pnbuf,
 	    cnp->cn_flags, 0, 0);