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Date:      Fri, 8 Feb 2019 04:18:17 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r343891 - in head/sys: kern sys
Message-ID:  <201902080418.x184IH9K091522@repo.freebsd.org>
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Author: kib
Date: Fri Feb  8 04:18:17 2019
New Revision: 343891
URL: https://svnweb.freebsd.org/changeset/base/343891

Log:
  Fix renameat(2) for CAPABILITIES kernels.
  
  When renameat(2) is used with:
  - absolute path for to;
  - tofd not set to AT_FDCWD;
  - the target exists
  kern_renameat() requires CAP_UNLINK capability on tofd, but
  corresponding namei ni_filecap is not initialized at all because the
  lookup is absolute.  As result, the check was done against empty filecap
  and syscall fails erronously.
  
  Fix it by creating a return flags namei member and reporting if the
  lookup was absolute, then do not touch to.ni_filecaps at all.
  
  PR:	222258
  Reviewed by:	jilles, ngie
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week
  X-MFC-note:	KBI breakage
  Differential revision:	https://reviews.freebsd.org/D19096

Modified:
  head/sys/kern/vfs_lookup.c
  head/sys/kern/vfs_syscalls.c
  head/sys/sys/namei.h

Modified: head/sys/kern/vfs_lookup.c
==============================================================================
--- head/sys/kern/vfs_lookup.c	Fri Feb  8 04:06:48 2019	(r343890)
+++ head/sys/kern/vfs_lookup.c	Fri Feb  8 04:18:17 2019	(r343891)
@@ -410,6 +410,7 @@ namei(struct nameidata *ndp)
 	dp = NULL;
 	cnp->cn_nameptr = cnp->cn_pnbuf;
 	if (cnp->cn_pnbuf[0] == '/') {
+		ndp->ni_resflags |= NIRES_ABS;
 		error = namei_handle_root(ndp, &dp);
 	} else {
 		if (ndp->ni_startdir != NULL) {
@@ -1302,6 +1303,7 @@ NDINIT_ALL(struct nameidata *ndp, u_long op, u_long fl
 	ndp->ni_dirp = namep;
 	ndp->ni_dirfd = dirfd;
 	ndp->ni_startdir = startdir;
+	ndp->ni_resflags = 0;
 	filecaps_init(&ndp->ni_filecaps);
 	ndp->ni_cnd.cn_thread = td;
 	if (rightsp != NULL)

Modified: head/sys/kern/vfs_syscalls.c
==============================================================================
--- head/sys/kern/vfs_syscalls.c	Fri Feb  8 04:06:48 2019	(r343890)
+++ head/sys/kern/vfs_syscalls.c	Fri Feb  8 04:18:17 2019	(r343891)
@@ -3544,10 +3544,10 @@ again:
 			goto out;
 		}
 #ifdef CAPABILITIES
-		if (newfd != AT_FDCWD) {
+		if (newfd != AT_FDCWD && (tond.ni_resflags & NIRES_ABS) == 0) {
 			/*
 			 * If the target already exists we require CAP_UNLINKAT
-			 * from 'newfd'.
+			 * from 'newfd', when newfd was used for the lookup.
 			 */
 			error = cap_check(&tond.ni_filecaps.fc_rights,
 			    &cap_unlinkat_rights);

Modified: head/sys/sys/namei.h
==============================================================================
--- head/sys/sys/namei.h	Fri Feb  8 04:06:48 2019	(r343890)
+++ head/sys/sys/namei.h	Fri Feb  8 04:18:17 2019	(r343891)
@@ -88,6 +88,10 @@ struct nameidata {
 	struct	vnode *ni_vp;		/* vnode of result */
 	struct	vnode *ni_dvp;		/* vnode of intermediate directory */
 	/*
+	 * Results: flags returned from namei
+	 */
+	u_int	ni_resflags;
+	/*
 	 * Shared between namei and lookup/commit routines.
 	 */
 	size_t	ni_pathlen;		/* remaining chars in path */
@@ -158,6 +162,11 @@ struct nameidata {
 #define	TRAILINGSLASH	0x10000000 /* path ended in a slash */
 #define	NOCAPCHECK	0x20000000 /* do not perform capability checks */
 #define	PARAMASK	0x3ffffe00 /* mask of parameter descriptors */
+
+/*
+ * Namei results flags
+ */
+#define	NIRES_ABS	0x00000001 /* Path was absolute */
 
 /*
  * Flags in ni_lcf, valid for the duration of the namei call.

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