On Fri, Sep 01, 2023 at 04:50:53PM +0200, Michał Cłapiński wrote:
On Fri, Sep 1, 2023 at 2:56 PM Christian Brauner brauner@kernel.org wrote:
On Thu, Aug 31, 2023 at 10:36:46PM +0200, Michal Clapinski wrote:
Add a way to check if an fd points to the memfd's original open fd (the one created by memfd_create). Useful because only the original open fd can be both writable and executable.
Signed-off-by: Michal Clapinski mclapinski@google.com
fs/fcntl.c | 3 +++ include/uapi/linux/fcntl.h | 9 +++++++++ 2 files changed, 12 insertions(+)
diff --git a/fs/fcntl.c b/fs/fcntl.c index e871009f6c88..301527e07a4d 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -419,6 +419,9 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg, case F_SET_RW_HINT: err = fcntl_rw_hint(filp, cmd, arg); break;
case F_CHECK_ORIGINAL_MEMFD:err = !(filp->f_mode & FMODE_WRITER);break;Honestly, make this an ioctl on memfds. This is so specific that it really doesn't belong into fcntl().
I've never touched ioctls but if I'm correct, I can't just add it to memfd. I would have to add it to the underlying fs, so hugetlbfs and shmem (which I think can be defined as ramfs so also there). File sealing fcntl is already memfd specific. Are you sure ioctl will be a better idea?
Does this check "mean" anything for other files? Because if it's generically useful (and got renamed) it maybe would be right for fcntl...