Patch "bpf: In bpf_task_fd_query use fget_task" 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

    bpf: In bpf_task_fd_query use fget_task

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:
     bpf-in-bpf_task_fd_query-use-fget_task.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 202ee117eebaca9d39e104672b4b690bda9c9c27
Author: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Date:   Fri Nov 20 17:14:22 2020 -0600

    bpf: In bpf_task_fd_query use fget_task
    
    [ Upstream commit b48845af0152d790a54b8ab78cc2b7c07485fc98 ]
    
    Use the helper fget_task to simplify bpf_task_fd_query.
    
    As well as simplifying the code this removes one unnecessary increment of
    struct files_struct.  This unnecessary increment of files_struct.count can
    result in exec unnecessarily unsharing files_struct and breaking posix
    locks, and it can result in fget_light having to fallback to fget reducing
    performance.
    
    This simplification comes from the observation that none of the
    callers of get_files_struct actually need to call get_files_struct
    that was made when discussing[1] exec and posix file locks.
    
    [1] https://lkml.kernel.org/r/20180915160423.GA31461@xxxxxxxxxx
    Suggested-by: Oleg Nesterov <oleg@xxxxxxxxxx>
    v1: https://lkml.kernel.org/r/20200817220425.9389-5-ebiederm@xxxxxxxxxxxx
    Link: https://lkml.kernel.org/r/20201120231441.29911-5-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/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e1bee8cd34044..fbe7f8e2b022c 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3929,7 +3929,6 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
 	pid_t pid = attr->task_fd_query.pid;
 	u32 fd = attr->task_fd_query.fd;
 	const struct perf_event *event;
-	struct files_struct *files;
 	struct task_struct *task;
 	struct file *file;
 	int err;
@@ -3949,23 +3948,11 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
 	if (!task)
 		return -ENOENT;
 
-	files = get_files_struct(task);
-	put_task_struct(task);
-	if (!files)
-		return -ENOENT;
-
 	err = 0;
-	spin_lock(&files->file_lock);
-	file = fcheck_files(files, fd);
+	file = fget_task(task, fd);
+	put_task_struct(task);
 	if (!file)
-		err = -EBADF;
-	else
-		get_file(file);
-	spin_unlock(&files->file_lock);
-	put_files_struct(files);
-
-	if (err)
-		goto out;
+		return -EBADF;
 
 	if (file->f_op == &bpf_link_fops) {
 		struct bpf_link *link = file->private_data;
@@ -4005,7 +3992,6 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
 	err = -ENOTSUPP;
 put_file:
 	fput(file);
-out:
 	return err;
 }