Make verification match the new restricted directory symlink behavior

Only follow directory symlinks owned by target directory owner or root
during verification to match the behavior of fsmVerify() in the new
CVE-2017-7500 world order.

The code is klunkier than it should and the logic should use common code
with fsmVerify() instead of duplicating it here, but that needs more
changes than is comfortable to backport so starting with this.

Also worth noting that the previous "follow the link" logic from
commit 3ccd774 was not quite right,
it'd fail with RPMVERIFY_LSTATFAIL on a broken symlink when it should've
ran verification on the symlink itself. This behavior is fixed here too.

Finally, once again fakechroot gets in the way and forces the related
verify testcase to be changed to be able to create a valid link. Reuse
the replacement testcase for the purpose and add another case for
verifying an invalid link.

lib/verify.c

@@ -94,9 +94,18 @@ rpmVerifyAttrs rpmfilesVerify(rpmfiles fi, int ix, rpmVerifyAttrs omitMask)
     }
 
     /* If we expected a directory but got a symlink to one, follow the link */
-    if (S_ISDIR(fmode) && S_ISLNK(sb.st_mode) && stat(fn, &sb) != 0) {
-	vfy |= RPMVERIFY_LSTATFAIL;
-	goto exit;
+    if (S_ISDIR(fmode) && S_ISLNK(sb.st_mode)) {
+	struct stat dsb;
+	/* ...if it actually points to a directory  */
+	if (stat(fn, &dsb) == 0 && S_ISDIR(dsb.st_mode)) {
+	    uid_t fuid;
+	    /* ...and is by a legit user, to match fsmVerify() behavior */
+	    if (sb.st_uid == 0 ||
+			(rpmugUid(rpmfilesFUser(fi, ix), &fuid) == 0 &&
+			 sb.st_uid == fuid)) {
+		sb = dsb; /* struct assignment */
+	    }
+	}
     }
 
     /* Links have no mode, other types have no linkto */

tests/rpmverify.at

@@ -69,18 +69,56 @@ AT_KEYWORDS([verify])
 AT_CHECK([
 RPMDB_CLEAR
 RPMDB_INIT
+tf="${RPMTEST}"/opt/foo
+rm -rf "${RPMTEST}"/opt/*
+rm -rf "${TOPDIR}"
 
-runroot rpm -U --nodeps --noscripts --ignorearch --ignoreos \
-	/data/RPMS/hello-1.0-1.i386.rpm
-mv "${RPMTEST}"/usr/share/doc/hello-1.0 "${RPMTEST}"/usr/share/doc/hello-1.0.orig
-ln -s hello-1.0.orig "${RPMTEST}"/usr/share/doc/hello-1.0
-runroot rpm -Vva --nodeps --nouser --nogroup
-rm -rf "${RPMTEST}"/usr/share/doc/
+runroot rpmbuild --quiet -bb \
+        --define "ver 1.0" \
+        --define "filetype datadir" \
+        --define "filedata README1" \
+        --define "user $(id -u -n)" \
+          /data/SPECS/replacetest.spec
+
+runroot rpm -U /build/RPMS/noarch/replacetest-1.0-1.noarch.rpm
+mv "${RPMTEST}"/opt/foo "${RPMTEST}"/opt/was
+ln -s was "${RPMTEST}"/opt/foo
+runroot rpm -Vv replacetest
 ],
 [0],
-[.........    /usr/local/bin/hello
-.........    /usr/share/doc/hello-1.0
-.........  d /usr/share/doc/hello-1.0/FAQ
+[.........    /opt/foo
+.........    /opt/foo/README1
+.........    /opt/goo
+.........    /opt/zoo
+],
+[])
+AT_CLEANUP
+
+AT_SETUP([directory replaced with an invalid directory symlink])
+AT_KEYWORDS([verify])
+AT_CHECK([
+RPMDB_CLEAR
+RPMDB_INIT
+tf="${RPMTEST}"/opt/foo
+rm -rf "${RPMTEST}"/opt/*
+rm -rf "${TOPDIR}"
+
+runroot rpmbuild --quiet -bb \
+        --define "ver 1.0" \
+        --define "filetype datadir" \
+        --define "filedata README1" \
+          /data/SPECS/replacetest.spec
+
+runroot rpm -U /build/RPMS/noarch/replacetest-1.0-1.noarch.rpm
+mv "${RPMTEST}"/opt/foo "${RPMTEST}"/opt/was
+ln -s was "${RPMTEST}"/opt/foo
+runroot rpm -Vv --nouser --nogroup replacetest
+],
+[1],
+[....L....    /opt/foo
+.........    /opt/foo/README1
+.........    /opt/goo
+.........    /opt/zoo
 ],
 [])
 AT_CLEANUP