[v2,19/24] file: In f_dupfd read RLIMIT_NOFILE once.

Submitted by Eric W. Biederman on Nov. 20, 2020, 11:14 p.m.


Message ID 20201120231441.29911-19-ebiederm@xmission.com
State New
Series "exec: Move unshare_files and guarantee files_struct.count is correct"
Headers show

Commit Message

Eric W. Biederman Nov. 20, 2020, 11:14 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.

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
v1: https://lkml.kernel.org/r/20200817220425.9389-15-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
 fs/file.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

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diff --git a/fs/file.c b/fs/file.c
index 0d4ec0fa23b3..07e25f1b9dfd 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -538,9 +538,9 @@  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)
@@ -1175,10 +1175,11 @@  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) {
 		fd_install(err, file);