[15/17] file: In f_dupfd read RLIMIT_NOFILE once.

Submitted by Eric W. Biederman on Aug. 17, 2020, 10:04 p.m.

Details

Message ID 20200817220425.9389-15-ebiederm@xmission.com
State New
Series "Series without cover letter"
Headers show

Commit Message

Eric W. Biederman Aug. 17, 2020, 10:04 p.m.
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.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 fs/file.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

Patch hide | download patch | download mbox

diff --git a/fs/file.c b/fs/file.c
index 1a755811669d..505b2e81ad3e 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -523,9 +523,9 @@  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)
@@ -1158,10 +1158,11 @@  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);

Comments

Christian Brauner Aug. 18, 2020, 10:12 a.m.
On Mon, Aug 17, 2020 at 05:04:23PM -0500, Eric W. Biederman wrote:
> 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.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>