Re: [nfs-utils PATCH] Don't allow junction tests to trigger automounts

[Steve Dickson <steved@redhat.com>]

On 12/13/22 11:01 AM, Jeff Layton wrote:
> 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
> Reported-by: JianHong Yin <jiyin@redhat.com>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
Committed... (tag: nfs-utils-2-6-3-rc6)

steved
> ---
>   support/junction/junction.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/support/junction/junction.c b/support/junction/junction.c
> index 41cce261cb52..0628bb0ffffb 100644
> --- a/support/junction/junction.c
> +++ b/support/junction/junction.c
> @@ -63,7 +63,7 @@ junction_open_path(const char *pathname, int *fd)
>   	if (pathname == NULL || fd == NULL)
>   		return FEDFS_ERR_INVAL;
>   
> -	tmp = open(pathname, O_DIRECTORY);
> +	tmp = open(pathname, O_PATH|O_DIRECTORY);
>   	if (tmp == -1) {
>   		switch (errno) {
>   		case EPERM:
> @@ -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);