[PATCH] fs/xattr: actually support O_PATH fds in *xattrat() syscalls

[Mike Yuan]

Cited from commit message of original patch [1]:

> One use case will be setfiles(8) setting SELinux file contexts
> ("security.selinux") without race conditions and without a file
> descriptor opened with read access requiring SELinux read permission.

Also, generally all *at() syscalls operate on O_PATH fds, unlike
f*() ones. Yet the O_PATH fds are rejected by *xattrat() syscalls
in the final version merged into tree. Instead, let's switch things
to CLASS(fd_raw).

Note that there's one side effect: f*xattr() starts to work with
O_PATH fds too. It's not clear to me whether this is desirable
(e.g. fstat() accepts O_PATH fds as an outlier).

[1] https://lore.kernel.org/all/20240426162042.191916-1-cgoettsche@xxxxxxxxxxxxx/

Fixes: 6140be90ec70 ("fs/xattr: add *at family syscalls")
Signed-off-by: Mike Yuan <me@xxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Göttsche <cgzones@xxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
 fs/xattr.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index 02bee149ad96..15df71e56187 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -704,7 +704,7 @@ static int path_setxattrat(int dfd, const char __user *pathname,
 
 	filename = getname_maybe_null(pathname, at_flags);
 	if (!filename) {
-		CLASS(fd, f)(dfd);
+		CLASS(fd_raw, f)(dfd);
 		if (fd_empty(f))
 			error = -EBADF;
 		else
@@ -848,7 +848,7 @@ static ssize_t path_getxattrat(int dfd, const char __user *pathname,
 
 	filename = getname_maybe_null(pathname, at_flags);
 	if (!filename) {
-		CLASS(fd, f)(dfd);
+		CLASS(fd_raw, f)(dfd);
 		if (fd_empty(f))
 			return -EBADF;
 		return file_getxattr(fd_file(f), &ctx);
@@ -978,7 +978,7 @@ static ssize_t path_listxattrat(int dfd, const char __user *pathname,
 
 	filename = getname_maybe_null(pathname, at_flags);
 	if (!filename) {
-		CLASS(fd, f)(dfd);
+		CLASS(fd_raw, f)(dfd);
 		if (fd_empty(f))
 			return -EBADF;
 		return file_listxattr(fd_file(f), list, size);
@@ -1079,7 +1079,7 @@ static int path_removexattrat(int dfd, const char __user *pathname,
 
 	filename = getname_maybe_null(pathname, at_flags);
 	if (!filename) {
-		CLASS(fd, f)(dfd);
+		CLASS(fd_raw, f)(dfd);
 		if (fd_empty(f))
 			return -EBADF;
 		return file_removexattr(fd_file(f), &kname);

base-commit: a86bf2283d2c9769205407e2b54777c03d012939
-- 
2.48.1