commit cdbef4e97a1cbc68cbaf16ba57d71858d2c69973
Author: Jeff Layton <jlayton@kernel.org>
Date:   Tue Jan 10 09:37:25 2023 -0500

    nfs-utils: Don't allow junction tests to trigger automounts
    
    JianHong reported some strange behavior with automounts on an nfs server
    without an explicit pseudoroot. When clients issued a readdir in the
    pseudoroot, automounted directories that were not yet mounted would show
    up even if they weren't exported, though the clients wouldn't be able to
    do anything with them.
    
    The issue was that triggering the automount on a directory would cause
    the mountd upcall to time out, which would cause nfsd to include the
    automounted dentry in the readdir response. Eventually, the automount
    would work and report that it wasn't exported and subsequent attempts to
    access the dentry would (properly) fail.
    
    We never want mountd to trigger an automount. The kernel should do that
    if it wants to use it. Change the junction checks to do an O_PATH open
    and use fstatat with AT_NO_AUTOMOUNT.
    
    Cc: Chuck Lever <chuck.lever@oracle.com>
    Link: https://bugzilla.redhat.com/show_bug.cgi?id=2148353
    Link: https://bugzilla.kernel.org/show_bug.cgi?id=216777
    Reported-by: JianHong Yin <jiyin@redhat.com>
    Signed-off-by: Jeff Layton <jlayton@kernel.org>
    Signed-off-by: Steve Dickson <steved@redhat.com>

diff --git a/support/junction/junction.c b/support/junction/junction.c
index 41cce26..0628bb0 100644
--- a/support/junction/junction.c
+++ b/support/junction/junction.c
@@ -93,7 +93,7 @@ junction_is_directory(int fd, const char *path)
 {
 	struct stat stb;
 
-	if (fstat(fd, &stb) == -1) {
+	if (fstatat(fd, "", &stb, AT_NO_AUTOMOUNT|AT_EMPTY_PATH) == -1) {
 		xlog(D_GENERAL, "%s: failed to stat %s: %m",
 				__func__, path);
 		return FEDFS_ERR_ACCESS;
@@ -121,7 +121,7 @@ junction_is_sticky_bit_set(int fd, const char *path)
 {
 	struct stat stb;
 
-	if (fstat(fd, &stb) == -1) {
+	if (fstatat(fd, "", &stb, AT_NO_AUTOMOUNT|AT_EMPTY_PATH) == -1) {
 		xlog(D_GENERAL, "%s: failed to stat %s: %m",
 				__func__, path);
 		return FEDFS_ERR_ACCESS;
@@ -155,7 +155,7 @@ junction_set_sticky_bit(int fd, const char *path)
 {
 	struct stat stb;
 
-	if (fstat(fd, &stb) == -1) {
+	if (fstatat(fd, "", &stb, AT_NO_AUTOMOUNT|AT_EMPTY_PATH) == -1) {
 		xlog(D_GENERAL, "%s: failed to stat %s: %m",
 			__func__, path);
 		return FEDFS_ERR_ACCESS;
@@ -393,7 +393,7 @@ junction_get_mode(const char *pathname, mode_t *mode)
 	if (retval != FEDFS_OK)
 		return retval;
 
-	if (fstat(fd, &stb) == -1) {
+	if (fstatat(fd, "", &stb, AT_NO_AUTOMOUNT|AT_EMPTY_PATH) == -1) {
 		xlog(D_GENERAL, "%s: failed to stat %s: %m",
 			__func__, pathname);
 		(void)close(fd);