Patch "file: Factor files_lookup_fd_locked out of fcheck_files" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    file: Factor files_lookup_fd_locked out of fcheck_files

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     file-factor-files_lookup_fd_locked-out-of-fcheck_fil.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit c33f7df863623f9e08f90dbaf8fd116a957fa688
Author: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Date:   Fri Nov 20 17:14:25 2020 -0600

    file: Factor files_lookup_fd_locked out of fcheck_files
    
    [ Upstream commit 120ce2b0cd52abe73e8b16c23461eb14df5a87d8 ]
    
    To make it easy to tell where files->file_lock protection is being
    used when looking up a file create files_lookup_fd_locked.  Only allow
    this function to be called with the file_lock held.
    
    Update the callers of fcheck and fcheck_files that are called with the
    files->file_lock held to call files_lookup_fd_locked instead.
    
    Hopefully this makes it easier to quickly understand what is going on.
    
    The need for better names became apparent in the last round of
    discussion of this set of changes[1].
    
    [1] https://lkml.kernel.org/r/CAHk-=wj8BQbgJFLa+J0e=iT-1qpmCRTbPAJ8gd6MJQ=kbRPqyQ@xxxxxxxxxxxxxx
    Link: https://lkml.kernel.org/r/20201120231441.29911-8-ebiederm@xxxxxxxxxxxx
    Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/file.c b/fs/file.c
index eb1e2b7220ac6..6a6b03ce4ad69 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -1158,7 +1158,7 @@ static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
 
 	spin_lock(&files->file_lock);
 	err = expand_files(files, newfd);
-	file = fcheck(oldfd);
+	file = files_lookup_fd_locked(files, oldfd);
 	if (unlikely(!file))
 		goto Ebadf;
 	if (unlikely(err < 0)) {
diff --git a/fs/locks.c b/fs/locks.c
index cbb5701ce9f37..873f97504bddf 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2536,14 +2536,15 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
 	 */
 	if (!error && file_lock->fl_type != F_UNLCK &&
 	    !(file_lock->fl_flags & FL_OFDLCK)) {
+		struct files_struct *files = current->files;
 		/*
 		 * We need that spin_lock here - it prevents reordering between
 		 * update of i_flctx->flc_posix and check for it done in
 		 * close(). rcu_read_lock() wouldn't do.
 		 */
-		spin_lock(&current->files->file_lock);
-		f = fcheck(fd);
-		spin_unlock(&current->files->file_lock);
+		spin_lock(&files->file_lock);
+		f = files_lookup_fd_locked(files, fd);
+		spin_unlock(&files->file_lock);
 		if (f != filp) {
 			file_lock->fl_type = F_UNLCK;
 			error = do_lock_file_wait(filp, cmd, file_lock);
@@ -2667,14 +2668,15 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
 	 */
 	if (!error && file_lock->fl_type != F_UNLCK &&
 	    !(file_lock->fl_flags & FL_OFDLCK)) {
+		struct files_struct *files = current->files;
 		/*
 		 * We need that spin_lock here - it prevents reordering between
 		 * update of i_flctx->flc_posix and check for it done in
 		 * close(). rcu_read_lock() wouldn't do.
 		 */
-		spin_lock(&current->files->file_lock);
-		f = fcheck(fd);
-		spin_unlock(&current->files->file_lock);
+		spin_lock(&files->file_lock);
+		f = files_lookup_fd_locked(files, fd);
+		spin_unlock(&files->file_lock);
 		if (f != filp) {
 			file_lock->fl_type = F_UNLCK;
 			error = do_lock_file_wait(filp, cmd, file_lock);
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index d58960f6ee524..2cca9bca3b3a3 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -35,7 +35,7 @@ static int seq_show(struct seq_file *m, void *v)
 		unsigned int fd = proc_fd(m->private);
 
 		spin_lock(&files->file_lock);
-		file = fcheck_files(files, fd);
+		file = files_lookup_fd_locked(files, fd);
 		if (file) {
 			struct fdtable *fdt = files_fdtable(files);
 
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 10e75b4c30a43..87be704268d26 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -91,6 +91,13 @@ static inline struct file *files_lookup_fd_raw(struct files_struct *files, unsig
 	return NULL;
 }
 
+static inline struct file *files_lookup_fd_locked(struct files_struct *files, unsigned int fd)
+{
+	RCU_LOCKDEP_WARN(!lockdep_is_held(&files->file_lock),
+			   "suspicious rcu_dereference_check() usage");
+	return files_lookup_fd_raw(files, fd);
+}
+
 static inline struct file *fcheck_files(struct files_struct *files, unsigned int fd)
 {
 	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&