* Re: [PATCH 0/4] uapi, vfs: Change the mount API UAPI [ver #2]
[not found] ` <20190516165021.GD17978@ZenIV.linux.org.uk>
@ 2019-05-16 20:23 ` Dmitry V. Levin
2019-05-17 6:54 ` Christian Brauner
2019-05-17 7:01 ` Christian Brauner
2019-05-17 7:13 ` David Howells
2 siblings, 1 reply; 6+ messages in thread
From: Dmitry V. Levin @ 2019-05-16 20:23 UTC (permalink / raw)
To: Al Viro
Cc: Christian Brauner, David Howells, torvalds, Arnd Bergmann,
linux-fsdevel, linux-kernel, linux-api
[looks like linux-abi is a typo, Cc'ed linux-api instead]
On Thu, May 16, 2019 at 05:50:22PM +0100, Al Viro wrote:
> [linux-abi cc'd]
>
> On Thu, May 16, 2019 at 06:31:52PM +0200, Christian Brauner wrote:
> > On Thu, May 16, 2019 at 05:22:59PM +0100, Al Viro wrote:
> > > On Thu, May 16, 2019 at 12:52:04PM +0100, David Howells wrote:
> > > >
> > > > Hi Linus, Al,
> > > >
> > > > Here are some patches that make changes to the mount API UAPI and two of
> > > > them really need applying, before -rc1 - if they're going to be applied at
> > > > all.
> > >
> > > I'm fine with 2--4, but I'm not convinced that cloexec-by-default crusade
> > > makes any sense. Could somebody give coherent arguments in favour of
> > > abandoning the existing conventions?
> >
> > So as I said in the commit message. From a userspace perspective it's
> > more of an issue if one accidently leaks an fd to a task during exec.
> >
> > Also, most of the time one does not want to inherit an fd during an
> > exec. It is a hazzle to always have to specify an extra flag.
> >
> > As Al pointed out to me open() semantics are not going anywhere. Sure,
> > no argument there at all.
> > But the idea of making fds cloexec by default is only targeted at fds
> > that come from separate syscalls. fsopen(), open_tree_clone(), etc. they
> > all return fds independent of open() so it's really easy to have them
> > cloexec by default without regressing anyone and we also remove the need
> > for a bunch of separate flags for each syscall to turn them into
> > cloexec-fds. I mean, those for syscalls came with 4 separate flags to be
> > able to specify that the returned fd should be made cloexec. The other
> > way around, cloexec by default, fcntl() to remove the cloexec bit is way
> > saner imho.
>
> Re separate flags - it is, in principle, a valid argument. OTOH, I'm not
> sure if they need to be separate - they all have the same value and
> I don't see any reason for that to change...
>
> Only tangentially related, but I wonder if something like close_range(from, to)
> would be a more useful approach... That kind of open-coded loops is not
> rare in userland and kernel-side code can do them much cheaper. Something
> like
> /* that exec is sensitive */
> unshare(CLONE_FILES);
> /* we don't want anything past stderr here */
> close_range(3, ~0U);
> execve(....);
> on the userland side of thing. Comments?
glibc people need a syscall to implement closefrom properly, see
https://sourceware.org/bugzilla/show_bug.cgi?id=10353#c14
--
ldv
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH 0/4] uapi, vfs: Change the mount API UAPI [ver #2]
2019-05-16 20:23 ` [PATCH 0/4] uapi, vfs: Change the mount API UAPI [ver #2] Dmitry V. Levin
@ 2019-05-17 6:54 ` Christian Brauner
0 siblings, 0 replies; 6+ messages in thread
From: Christian Brauner @ 2019-05-17 6:54 UTC (permalink / raw)
To: Dmitry V. Levin, Al Viro
Cc: David Howells, torvalds, Arnd Bergmann, linux-fsdevel,
linux-kernel, linux-api
On May 16, 2019 10:23:31 PM GMT+02:00, "Dmitry V. Levin" <ldv@altlinux.org> wrote:
>[looks like linux-abi is a typo, Cc'ed linux-api instead]
>
>On Thu, May 16, 2019 at 05:50:22PM +0100, Al Viro wrote:
>> [linux-abi cc'd]
>>
>> On Thu, May 16, 2019 at 06:31:52PM +0200, Christian Brauner wrote:
>> > On Thu, May 16, 2019 at 05:22:59PM +0100, Al Viro wrote:
>> > > On Thu, May 16, 2019 at 12:52:04PM +0100, David Howells wrote:
>> > > >
>> > > > Hi Linus, Al,
>> > > >
>> > > > Here are some patches that make changes to the mount API UAPI
>and two of
>> > > > them really need applying, before -rc1 - if they're going to be
>applied at
>> > > > all.
>> > >
>> > > I'm fine with 2--4, but I'm not convinced that cloexec-by-default
>crusade
>> > > makes any sense. Could somebody give coherent arguments in
>favour of
>> > > abandoning the existing conventions?
>> >
>> > So as I said in the commit message. From a userspace perspective
>it's
>> > more of an issue if one accidently leaks an fd to a task during
>exec.
>> >
>> > Also, most of the time one does not want to inherit an fd during an
>> > exec. It is a hazzle to always have to specify an extra flag.
>> >
>> > As Al pointed out to me open() semantics are not going anywhere.
>Sure,
>> > no argument there at all.
>> > But the idea of making fds cloexec by default is only targeted at
>fds
>> > that come from separate syscalls. fsopen(), open_tree_clone(), etc.
>they
>> > all return fds independent of open() so it's really easy to have
>them
>> > cloexec by default without regressing anyone and we also remove the
>need
>> > for a bunch of separate flags for each syscall to turn them into
>> > cloexec-fds. I mean, those for syscalls came with 4 separate flags
>to be
>> > able to specify that the returned fd should be made cloexec. The
>other
>> > way around, cloexec by default, fcntl() to remove the cloexec bit
>is way
>> > saner imho.
>>
>> Re separate flags - it is, in principle, a valid argument. OTOH, I'm
>not
>> sure if they need to be separate - they all have the same value and
>> I don't see any reason for that to change...
>>
>> Only tangentially related, but I wonder if something like
>close_range(from, to)
>> would be a more useful approach... That kind of open-coded loops is
>not
>> rare in userland and kernel-side code can do them much cheaper.
>Something
>> like
>> /* that exec is sensitive */
>> unshare(CLONE_FILES);
>> /* we don't want anything past stderr here */
>> close_range(3, ~0U);
>> execve(....);
>> on the userland side of thing. Comments?
>
>glibc people need a syscall to implement closefrom properly, see
>https://sourceware.org/bugzilla/show_bug.cgi?id=10353#c14
I have a prototype for close_range().
I'll send it out after rc1.
Christian
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 0/4] uapi, vfs: Change the mount API UAPI [ver #2]
[not found] ` <20190516165021.GD17978@ZenIV.linux.org.uk>
2019-05-16 20:23 ` [PATCH 0/4] uapi, vfs: Change the mount API UAPI [ver #2] Dmitry V. Levin
@ 2019-05-17 7:01 ` Christian Brauner
2019-05-17 7:13 ` David Howells
2 siblings, 0 replies; 6+ messages in thread
From: Christian Brauner @ 2019-05-17 7:01 UTC (permalink / raw)
To: Al Viro
Cc: David Howells, torvalds, Arnd Bergmann, linux-fsdevel,
linux-kernel, linux-api
On May 16, 2019 6:50:22 PM GMT+02:00, Al Viro <viro@zeniv.linux.org.uk> wrote:
>[linux-abi cc'd]
>
>On Thu, May 16, 2019 at 06:31:52PM +0200, Christian Brauner wrote:
>> On Thu, May 16, 2019 at 05:22:59PM +0100, Al Viro wrote:
>> > On Thu, May 16, 2019 at 12:52:04PM +0100, David Howells wrote:
>> > >
>> > > Hi Linus, Al,
>> > >
>> > > Here are some patches that make changes to the mount API UAPI and
>two of
>> > > them really need applying, before -rc1 - if they're going to be
>applied at
>> > > all.
>> >
>> > I'm fine with 2--4, but I'm not convinced that cloexec-by-default
>crusade
>> > makes any sense. Could somebody give coherent arguments in favour
>of
>> > abandoning the existing conventions?
>>
>> So as I said in the commit message. From a userspace perspective it's
>> more of an issue if one accidently leaks an fd to a task during exec.
>>
>> Also, most of the time one does not want to inherit an fd during an
>> exec. It is a hazzle to always have to specify an extra flag.
>>
>> As Al pointed out to me open() semantics are not going anywhere.
>Sure,
>> no argument there at all.
>> But the idea of making fds cloexec by default is only targeted at fds
>> that come from separate syscalls. fsopen(), open_tree_clone(), etc.
>they
>> all return fds independent of open() so it's really easy to have them
>> cloexec by default without regressing anyone and we also remove the
>need
>> for a bunch of separate flags for each syscall to turn them into
>> cloexec-fds. I mean, those for syscalls came with 4 separate flags to
>be
>> able to specify that the returned fd should be made cloexec. The
>other
>> way around, cloexec by default, fcntl() to remove the cloexec bit is
>way
>> saner imho.
>
>Re separate flags - it is, in principle, a valid argument. OTOH, I'm
>not
>sure if they need to be separate - they all have the same value and
>I don't see any reason for that to change...
One last thing I'd like to point out is that
we already have syscalls and ioctls that
return cloexec fds. So the consistency
argument is kinda dead.
If you still prefer to have cloexec flags
for the 4 new syscalls then yes,
if they could at least all have the same name
(FSMOUNT_CLOEXEC?) that would be good.
>
>Only tangentially related, but I wonder if something like
>close_range(from, to)
>would be a more useful approach... That kind of open-coded loops is
>not
>rare in userland and kernel-side code can do them much cheaper.
>Something
>like
> /* that exec is sensitive */
> unshare(CLONE_FILES);
> /* we don't want anything past stderr here */
> close_range(3, ~0U);
> execve(....);
>on the userland side of thing. Comments?
Said it before but, the list was mistyped so again:
I think that's a great idea.
I have a prototype for close_range(start, end, flags).
I'll wait after rc1 and then send it out.
Christian
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH 0/4] uapi, vfs: Change the mount API UAPI [ver #2]
[not found] ` <20190516165021.GD17978@ZenIV.linux.org.uk>
2019-05-16 20:23 ` [PATCH 0/4] uapi, vfs: Change the mount API UAPI [ver #2] Dmitry V. Levin
2019-05-17 7:01 ` Christian Brauner
@ 2019-05-17 7:13 ` David Howells
2019-05-17 7:25 ` Miklos Szeredi
2019-05-17 7:27 ` Christian Brauner
2 siblings, 2 replies; 6+ messages in thread
From: David Howells @ 2019-05-17 7:13 UTC (permalink / raw)
To: Christian Brauner
Cc: dhowells, Al Viro, torvalds, Arnd Bergmann, linux-fsdevel,
linux-kernel, linux-api
Christian Brauner <christian@brauner.io> wrote:
> If you still prefer to have cloexec flags
> for the 4 new syscalls then yes,
> if they could at least all have the same name
> (FSMOUNT_CLOEXEC?) that would be good.
They don't all have the same value (see OPEN_TREE_CLOEXEC).
Note that I also don't want to blindly #define them to O_CLOEXEC because it's
not necessarily the same value on all arches. Currently it can be 02000000,
010000000 or 0x400000 for instance, which means that if it's sharing a mask
with other flags, at least three bits have to be reserved for it or we have to
have arch-dependent bit juggling.
One thing I like about your approach of just making them O_CLOEXEC by default
and removing the constants is that it avoids this mess entirely.
David
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH 0/4] uapi, vfs: Change the mount API UAPI [ver #2]
2019-05-17 7:13 ` David Howells
@ 2019-05-17 7:25 ` Miklos Szeredi
2019-05-17 7:27 ` Christian Brauner
1 sibling, 0 replies; 6+ messages in thread
From: Miklos Szeredi @ 2019-05-17 7:25 UTC (permalink / raw)
To: David Howells
Cc: Christian Brauner, Al Viro, Linus Torvalds, Arnd Bergmann,
linux-fsdevel, linux-kernel, linux-api
On Fri, May 17, 2019 at 9:13 AM David Howells <dhowells@redhat.com> wrote:
>
> Christian Brauner <christian@brauner.io> wrote:
>
> > If you still prefer to have cloexec flags
> > for the 4 new syscalls then yes,
> > if they could at least all have the same name
> > (FSMOUNT_CLOEXEC?) that would be good.
>
> They don't all have the same value (see OPEN_TREE_CLOEXEC).
>
> Note that I also don't want to blindly #define them to O_CLOEXEC because it's
> not necessarily the same value on all arches. Currently it can be 02000000,
> 010000000 or 0x400000 for instance, which means that if it's sharing a mask
> with other flags, at least three bits have to be reserved for it or we have to
> have arch-dependent bit juggling.
>
> One thing I like about your approach of just making them O_CLOEXEC by default
> and removing the constants is that it avoids this mess entirely.
+1.
Confusion caused by inconsistency of naming is going to hurt more than
inconsistency of semantics wrt. open(2).
Thanks,
Miklos
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 0/4] uapi, vfs: Change the mount API UAPI [ver #2]
2019-05-17 7:13 ` David Howells
2019-05-17 7:25 ` Miklos Szeredi
@ 2019-05-17 7:27 ` Christian Brauner
1 sibling, 0 replies; 6+ messages in thread
From: Christian Brauner @ 2019-05-17 7:27 UTC (permalink / raw)
Cc: dhowells, Al Viro, torvalds, Arnd Bergmann, linux-fsdevel,
linux-kernel, linux-api
On May 17, 2019 9:13:26 AM GMT+02:00, David Howells <dhowells@redhat.com> wrote:
>Christian Brauner <christian@brauner.io> wrote:
>
>> If you still prefer to have cloexec flags
>> for the 4 new syscalls then yes,
>> if they could at least all have the same name
>> (FSMOUNT_CLOEXEC?) that would be good.
>
>They don't all have the same value (see OPEN_TREE_CLOEXEC).
>
>Note that I also don't want to blindly #define them to O_CLOEXEC
>because it's
>not necessarily the same value on all arches. Currently it can be
>02000000,
>010000000 or 0x400000 for instance, which means that if it's sharing a
>mask
>with other flags, at least three bits have to be reserved for it or we
>have to
>have arch-dependent bit juggling.
Ugh. Right, I forgot about that entirely.
Christian
>
>One thing I like about your approach of just making them O_CLOEXEC by
>default
>and removing the constants is that it avoids this mess entirely.
>
>David
^ permalink raw reply [flat|nested] 6+ messages in thread