Re: [PATCH] get rid of close_fd() misuse in cachefiles

[Al Viro <viro@zeniv.linux.org.uk>]

On Mon, Jun 03, 2024 at 09:53:26AM +0800, Gao Xiang wrote:
> Hi Al,
> 
> On 2024/6/3 08:11, Al Viro wrote:
> > 	fd_install() can't be undone by close_fd().  Just delay it
> > until the last failure exit - have cachefiles_ondemand_get_fd()
> > return the file on success (and ERR_PTR() on error) and let the
> > caller do fd_install() after successful copy_to_user()
> > 
> > Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> 
> It's a straight-forward fix to me, yet it will have a conflict with
> https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/commit/fs/cachefiles?h=vfs.fixes&id=4b4391e77a6bf24cba2ef1590e113d9b73b11039
> https://lore.kernel.org/all/20240522114308.2402121-10-libaokun@huaweicloud.com/
> 
> It also moves fd_install() to the end of the daemon_read() and tends
> to fix it for months, does it look good to you?

Looks sane (and my variant lacks put_unused_fd(), so it leaks the
descriptor).  OTOH, I suspect that my variant of calling conventions
makes for less churn - fd is available anyway, so you just need error
or file reference, and for that struct file * with ERR_PTR() for
errors works fine.

Anyway, your variant seems to be correct; feel free to slap my
ACKed-by on it.