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

Eric W. Biederman
2020-08-17T22:12:13Z

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(-)

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);
--
2.25.0