Patch "file: In f_dupfd read RLIMIT_NOFILE once." 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: In f_dupfd read RLIMIT_NOFILE once.

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-in-f_dupfd-read-rlimit_nofile-once.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 e8a8458ab206395b87d4c15d952abff7786cb84a
Author: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Date:   Fri Nov 20 17:14:36 2020 -0600

    file: In f_dupfd read RLIMIT_NOFILE once.
    
    Simplify the code, and remove the chance of races by reading
    RLIMIT_NOFILE only once in f_dupfd.
    
    Pass the read value of RLIMIT_NOFILE into alloc_fd which is the other
    location the rlimit was read in f_dupfd.  As f_dupfd is the only
    caller of alloc_fd this changing alloc_fd is trivially safe.
    
    Further this causes alloc_fd to take all of the same arguments as
    __alloc_fd except for the files_struct argument.
    
    Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
    v1: https://lkml.kernel.org/r/20200817220425.9389-15-ebiederm@xxxxxxxxxxxx
    Link: https://lkml.kernel.org/r/20201120231441.29911-19-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 a80deabe7f7dc..9e2b171b92520 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -567,9 +567,9 @@ int __alloc_fd(struct files_struct *files,
 	return error;
 }
 
-static int alloc_fd(unsigned start, unsigned flags)
+static int alloc_fd(unsigned start, unsigned end, unsigned flags)
 {
-	return __alloc_fd(current->files, start, rlimit(RLIMIT_NOFILE), flags);
+	return __alloc_fd(current->files, start, end, flags);
 }
 
 int __get_unused_fd_flags(unsigned flags, unsigned long nofile)
@@ -1235,10 +1235,11 @@ SYSCALL_DEFINE1(dup, unsigned int, fildes)
 
 int f_dupfd(unsigned int from, struct file *file, unsigned flags)
 {
+	unsigned long nofile = rlimit(RLIMIT_NOFILE);
 	int err;
-	if (from >= rlimit(RLIMIT_NOFILE))
+	if (from >= nofile)
 		return -EINVAL;
-	err = alloc_fd(from, flags);
+	err = alloc_fd(from, nofile, flags);
 	if (err >= 0) {
 		get_file(file);
 		fd_install(err, file);