Re: [PATCH] ksmbd: fix lookup on idmapped mounts

[Namjae Jeon <linkinjeon@kernel.org>]

2021-08-21 23:10 GMT+09:00, Christian Brauner <christian.brauner@ubuntu.com>:
> On Sat, Aug 21, 2021 at 09:09:28PM +0900, Namjae Jeon wrote:
>> 2021-08-21 20:39 GMT+09:00, Christian Brauner
>> <christian.brauner@ubuntu.com>:
>> > On Sat, Aug 21, 2021 at 01:11:17PM +0200, Christian Brauner wrote:
>> >> On Sat, Aug 21, 2021 at 02:59:21PM +0900, Namjae Jeon wrote:
>> >> > 2021-08-19 22:01 GMT+09:00, Christian Brauner
>> >> > <christian.brauner@ubuntu.com>:
>> >> > > On Thu, Aug 19, 2021 at 11:19:04AM +0900, Namjae Jeon wrote:
>> >> > >> > On Tue, Aug 17, 2021 at 08:30:55AM +0900, Namjae Jeon wrote:
>> >> > >> > > > From: Christian Brauner <christian.brauner@ubuntu.com>
>> >> > >> > > >
>> >> > >> > > > It's great that the new in-kernel ksmbd server will support
>> >> > >> > > > idmapped
>> >> > >> > > > mounts out of the box! However, lookup is currently broken.
>> >> > >> > > > Lookup
>> >> > >> > > > helpers such as lookup_one_len() call inode_permission()
>> >> > >> > > > internally
>> >> > >> > > > to ensure that the caller is privileged over the inode of
>> >> > >> > > > the
>> >> > >> > > > base
>> >> > >> > > > dentry they are trying to
>> >> > >> > lookup under. So the permission checking here is currently
>> >> > >> > wrong.
>> >> > >> > > >
>> >> > >> > > > Linux v5.15 will gain a new lookup helper lookup_one() that
>> >> > >> > > > does
>> >> > >> > > > take idmappings into account. I've added it as part of my
>> >> > >> > > > patch
>> >> > >> > > > series to make btrfs support idmapped mounts. The new helper
>> >> > >> > > > is
>> >> > >> > > > in
>> >> > >> > > > linux- next as part of David's (Sterba) btrfs for-next
>> >> > >> > > > branch
>> >> > >> > > > as
>> >> > >> > > > commit c972214c133b ("namei: add
>> >> > >> > mapping aware lookup helper").
>> >> > >> > > >
>> >> > >> > > > I've said it before during one of my first reviews: I would
>> >> > >> > > > very
>> >> > >> > > > much recommend adding fstests to
>> >> > >> > [1].
>> >> > >> > > > It already seems to have very rudimentary cifs support.
>> >> > >> > > > There
>> >> > >> > > > is a
>> >> > >> > > > completely generic idmapped mount testsuite that supports
>> >> > >> > > > idmapped
>> >> > >> > > > mounts.
>> >> > >> > > >
>> >> > >> > > > [1]:
>> >> > >> > > > https://git.kernel.org/pub/scm/fs/xfs/xfsprogs-dev.git/
>> >> > >> > > > Cc: Steve French <stfrench@microsoft.com>
>> >> > >> > > > Cc: Christoph Hellwig <hch@infradead.org>
>> >> > >> > > > Cc: Namjae Jeon <namjae.jeon@samsung.com>
>> >> > >> > > > Cc: Hyunchul Lee <hyc.lee@gmail.com>
>> >> > >> > > > Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
>> >> > >> > > > Cc: David Sterba <dsterba@suse.com>
>> >> > >> > > > Cc: linux-cifs@vger.kernel.org
>> >> > >> > > > Signed-off-by: Christian Brauner
>> >> > >> > > > <christian.brauner@ubuntu.com>
>> >> > >> > > > ---
>> >> > >> > > Hi Christian,
>> >> > >> > >
>> >> > >> > > > I merged David's for-next tree into cifsd-next to test this.
>> >> > >> > > > I
>> >> > >> > > > did
>> >> > >> > > > only compile test this. If someone gives me a clear set of
>> >> > >> > > > instructions how to test ksmbd on my local machine I can at
>> >> > >> > > > least
>> >> > >> > > > try to cut some time out of my week to do more reviews.
>> >> > >> > > > (I'd
>> >> > >> > > > especially like to see acl behavior with ksmbd.)
>> >> > >> > >
>> >> > >> > > There is "How to run ksmbd" section in patch cover letter.
>> >> > >> > >
>> >> > >> > > https://protect2.fireeye.com/v1/url?k=65ecaaf0-3a779239-65ed21bf-0cc47
>> >> > >> > > a336fae-53bc47005a1a97a9&q=1&e=e44c9f9f-d7ae-4768-8cc2-8f02d748fc6e&u=
>> >> > >> > > https%3A%2F%2Flkml.org%2Flkml%2F2021%2F8%2F5%2F54
>> >> > >> > >
>> >> > >> > > Let me know if it doesn't work well even if you try to run it
>> >> > >> > > with
>> >> > >> > > this step.
>> >> > >> > > And We will also check whether your patch work fine.
>> >> > >> > >
>> >> > >> > > >
>> >> > >> > > > One more thing, the tree for ksmbd was very hard to find. I
>> >> > >> > > > had
>> >> > >> > > > to
>> >> > >> > > > do a lot archeology to end up
>> >> > >> > at:
>> >> > >> > > >
>> >> > >> > > > git://git.samba.org/ksmbd.git
>> >> > >> > > This is also in the patch cover letter. See "Mailing list and
>> >> > >> > > repositories" section.
>> >> > >> > > I think that you can use :
>> >> > >> > >
>> >> > >> > > https://protect2.fireeye.com/v1/url?k=8af83a5d-d5630294-8af9b112-0cc47
>> >> > >> > > a336fae-e471ffbdb93d05b7&q=1&e=e44c9f9f-d7ae-4768-8cc2-8f02d748fc6e&u=
>> >> > >> > > https%3A%2F%2Fgithub.com%2Fnamjaejeon%2Fsmb3-kernel%2Ftree%2Fksmbd-v7-
>> >> > >> > > series
>> >> > >> > >
>> >> > >> > > >
>> >> > >> > > > Would be appreciated if this tree could be reflected in
>> >> > >> > > > MAINTAINERS
>> >> > >> > > > or somewhere else. The github repos with the broken out
>> >> > >> > > > patches/module aren't really that helpful.
>> >> > >> > > Okay, I will add git address of ksmbd in MAINTAINERS on next
>> >> > >> > > spin.
>> >> > >> > >
>> >> > >> > > >
>> >> > >> > > > Thanks!
>> >> > >> > > > Christian
>> >> > >> > > Really thanks for your review and I will apply this patch
>> >> > >> > > after
>> >> > >> > > checking it.
>> >> > >> >
>> >> > >> > Thank your for the pointers.
>> >> > >> >
>> >> > >> > Ok, so I've been taking the time to look into cifs and ksmbd
>> >> > >> > today.
>> >> > >> > My
>> >> > >> > mental model was wrong. There
>> >> > >> > are two things to consider here:
>> >> > >> >
>> >> > >> > 1. server: idmapped mounts with ksmbd
>> >> > >> > 2. client: idmapped mounts with cifs
>> >> > >> >
>> >> > >> > Your patchset adds support for 1.
>> >> > >> Right.
>> >> > >>
>> >> > >> > Let's say I have the following ksmbd config:
>> >> > >> >
>> >> > >> > root@f2-vm:~# cat /etc/ksmbd/smb.conf
>> >> > >> > [global]
>> >> > >> >         netbios name = SMBD
>> >> > >> >         server max protocol = SMB3
>> >> > >> > [test]
>> >> > >> >         path = /opt
>> >> > >> >         writeable = yes
>> >> > >> >         comment = TEST
>> >> > >> >         read only = no
>> >> > >> >
>> >> > >> > So /opt can be an idmapped mount and ksmb would know how to
>> >> > >> > deal
>> >> > >> > with
>> >> > >> > that correctly, i.e. you could
>> >> > >> > do:
>> >> > >> >
>> >> > >> > mount-idmapped --map-mount=b:1000:0:1 /opt /opt
>> >> > >> >
>> >> > >> > ksmbd.mountd
>> >> > >> >
>> >> > >> > and ksmbd would take the idmapping of /opt into account.
>> >> > >> Right.
>> >> > >>
>> >> > >> >
>> >> > >> > That however is different from 2. which is cifs itself being
>> >> > >> > idmappable.
>> >> > >> Right.
>> >> > >>
>> >> > >> > Whether or not that makes sense or is needed will need some
>> >> > >> > thinking.
>> >> > >> >
>> >> > >> > In any case, this has consequences for xfstests and now I
>> >> > >> > understand
>> >> > >> > your earlier confusion. In
>> >> > >> > another mail you pointed out that cifs reports that idmapped
>> >> > >> > mounts
>> >> > >> > are
>> >> > >> > not supported. That is correct
>> >> > >> > insofar as it means 2. is not supported, i.e. you can't do:
>> >> > >> Right.
>> >> > >>
>> >> > >> >
>> >> > >> > mount -t cifs -o username=foo,password=bar //server/files /mnt
>> >> > >> >
>> >> > >> > and then
>> >> > >> >
>> >> > >> > mount-idmapped --map-mount=b:1000:0:1 /mnt /mnt
>> >> > >> >
>> >> > >> > but that's also not what you want in order to test for ksmbd.
>> >> > >> > What
>> >> > >> > you
>> >> > >> > want is to test 1.
>> >> > >> Right. So we have manually tested it, not xfstests.
>> >> > >>
>> >> > >> >
>> >> > >> > So your test setup would require you to setup an idmapped mount
>> >> > >> > and
>> >> > >> > have
>> >> > >> > ksmbd use that which can then
>> >> > >> > be mounted by a client.
>> >> > >> >
>> >> > >> > With your instructions I was at least able to get a ksmb
>> >> > >> > instance
>> >> > >> > running and be able to mount a
>> >> > >> > client with -t cifs. All on the same machine, i.e. my server is
>> >> > >> > localhost.
>> >> > >> Okay.
>> >> > >>
>> >> > >> >
>> >> > >> > However, I need to dig a bit into the semantics to make better
>> >> > >> > assertions about what's going on.
>> >> > >> Okay. And I have applied your patch to ksmbd.
>> >> > >>
>> >> > >> >
>> >> > >> > Are unix extension supported with ksmb? Everytime I try to use
>> >> > >> > "posix"
>> >> > >> > as a mount option with mount -t cifs -o //127.0.0.1/test /mnt I
>> >> > >> > get
>> >> > >> > "uid=0" and "gid=0" and "noposix".
>> >> > >> > I do set "unix extensions = yes" in both the samba and ksmbd
>> >> > >> > smb.conf.
>> >> > >> With posix mount option, It should work. It worked well before but
>> >> > >> it
>> >> > >> is
>> >> > >> strange now.
>> >> > >>
>> >> > >> I'm not sure this is the correct fix, But could you please try to
>> >> > >> mount
>> >> > >> with the below change ?
>> >> > >>
>> >> > >> diff --git a/fs/cifs/fs_context.c b/fs/cifs/fs_context.c
>> >> > >> index eed59bc1d913..5fd0b0ddcc57 100644
>> >> > >> --- a/fs/cifs/fs_context.c
>> >> > >> +++ b/fs/cifs/fs_context.c
>> >> > >> @@ -1268,8 +1268,10 @@ static int
>> >> > >> smb3_fs_context_parse_param(struct
>> >> > >> fs_context *fc,
>> >> > >>         case Opt_unix:
>> >> > >>                 if (result.negated)
>> >> > >>                         ctx->linux_ext = 0;
>> >> > >> -               else
>> >> > >> +               else {
>> >> > >> +                       ctx->linux_ext = 1;
>> >> > >>                         ctx->no_linux_ext = 1;
>> >> > >> +               }
>> >> > >>                 break;
>> >> > >>         case Opt_nocase:
>> >> > >>                 ctx->nocase = 1;
>> >> > >
>> >> > > That stops the bleeding indeed. :)
>> >> > Okay, sorry for late response.
>> >> > > I think a slightly nicer fix might be:
>> >> > >
>> >> > > diff --git a/fs/cifs/fs_context.c b/fs/cifs/fs_context.c
>> >> > > index eed59bc1d913..424b8dc2232e 100644
>> >> > > --- a/fs/cifs/fs_context.c
>> >> > > +++ b/fs/cifs/fs_context.c
>> >> > > @@ -1269,7 +1269,8 @@ static int
>> >> > > smb3_fs_context_parse_param(struct
>> >> > > fs_context *fc,
>> >> > >                 if (result.negated)
>> >> > >                         ctx->linux_ext = 0;
>> >> > >                 else
>> >> > > -                       ctx->no_linux_ext = 1;
>> >> > > +                       ctx->linux_ext = 1;
>> >> > > +               ctx->no_linux_ext = !ctx->linux_ext;
>> >> > >                 break;
>> >> > >         case Opt_nocase:
>> >> > >                 ctx->nocase = 1;
>> >> > >
>> >> > > So with this patch applied I got unix permissions working after
>> >> > > all.
>> >> > > So
>> >> > > I was able to do some more testing.
>> >> > Okay.
>> >> > >
>> >> > > Just a few questions (independent of idmapped mounts):
>> >> > >
>> >> > > 1. Are the "uid=" and "gid=" mount options ignored when
>> >> > > "username="
>> >> > > is
>> >> > >    specified and "posix" is specified?
>> >> > >
>> >> > >    It seems that "uid=" and "gid=" have are silently ignored when
>> >> > >    "posix' is set. They are neither used to report file ownership
>> >> > > under
>> >> > >    the cifs mountpoint nor are they relevant when determining
>> >> > > ownership
>> >> > >    on disk?
>> >> > >
>> >> > >    As an example, assume I have added a user "foo" with uid 1000
>> >> > > to
>> >> > >    ksmbd via:
>> >> > >
>> >> > >            ksmbd.adduser -a foo
>> >> > >
>> >> > >    And I mounted a share via:
>> >> > >
>> >> > >            mount -t cifs -o
>> >> > > username=foo,password=bar,posix,uid=1234,gid=1234,forceuid,forcegid
>> >> > > //127.0.0.1/test /mnt
>> >> > >
>> >> > >    i) Ownership in /mnt appears posix-correct, i.e. "uid=" and
>> >> > > "gid="
>> >> > > have
>> >> > >       no effect on the reported ownership.
>> >> > >
>> >> > >    ii) Assume I'm logged in as the root user with uid 0. If I
>> >> > > create
>> >> > >        file or directory in /mnt it will be owned by user foo,
>> >> > > i.e.
>> >> > > uid
>> >> > >        1000, i.e., the "uid=1234" and "gid=1234" mount option have
>> >> > > zero
>> >> > >        effect on the ownership of the files?
>> >> > >
>> >> > > 2. Are the "uid=" and "gid=" options ignored for permission
>> >> > > checking
>> >> > >    when "posix" is specified?
>> >> > >
>> >> > > 3. Am I correct in assuming that there is no mount option that
>> >> > > makes
>> >> > >    chown() or chmod() have an actual effect.
>> >> > That will be an answer for 1,2, 3 question. There are mount options
>> >> > for
>> >> > this.
>> >> >  1. modefromsid
>> >> >  2. idsfromsid
>> >> >
>> >> > You can use this mount option and please check it.
>> >>
>> >> Thank you! This works and finally I can hit some codepaths I wasn't
>> >> able
>> >> to until now.
>> >>
>> >> > >
>> >> > >    cifs seems to have support for it but the ksmbd server doesn't
>> >> > > seem
>> >> > >    to?
>> >> > No, you need to use mount options for this as I said.
>> >> > ksmbd have supported it but I found an issue related to chown and
>> >> > have
>> >> > fixed.
>> >> >
>> >> > Could you please check the below git branch (pulled David'tree +
>> >> > ksmbd
>> >> > fixes) ?
>> >> >
>> >> >   git clone --branch=for-christian
>> >> > https://github.com/namjaejeon/smb3-kernel
>> >>
>> >> Thanks, I've pulled that branch.
>> >
>> > There's two problems in this patch. I'll post and point out here
>> > quickly, if you don't mind:
>> Thanks for your reiview!
>> >
>> > commit fd7d13c387798cbc3abd68ecc07b2c868c6d96cb
>> > Author: Namjae Jeon <namjae.jeon@samsung.com>
>> > Date:   Sat Aug 21 14:39:43 2021 +0900
>> >
>> >     ksmbd: fix permission check issue on chown and chmod
>> >
>> >     When commanding chmod and chown on cifs&ksmbd, ksmbd allows it
>> > without
>> > file
>> >     permissions check. There is code to check it in settattr_prepare.
>> >     Instead of setting the inode directly, update the mode and uid/gid
>> >     through notify_change.
>> >
>> >     Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
>> >     Signed-off-by: Steve French <stfrench@microsoft.com>
>> >
>> > diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
>> > index 0131997c2177..d329ea49fa14 100644
>> > --- a/fs/ksmbd/smb2pdu.c
>> > +++ b/fs/ksmbd/smb2pdu.c
>> > @@ -5861,10 +5861,15 @@ int smb2_set_info(struct ksmbd_work *work)
>> >                 break;
>> >         case SMB2_O_INFO_SECURITY:
>> >                 ksmbd_debug(SMB, "GOT SMB2_O_INFO_SECURITY\n");
>> > +               if (ksmbd_override_fsids(work)) {
>> > +                       rc = -ENOMEM;
>> > +                       goto err_out;
>> > +               }
>> >                 rc = smb2_set_info_sec(fp,
>> >
>> > le32_to_cpu(req->AdditionalInformation),
>> >                                        req->Buffer,
>> >                                        le32_to_cpu(req->BufferLength));
>> > +               ksmbd_revert_fsids(work);
>> >                 break;
>> >         default:
>> >                 rc = -EOPNOTSUPP;
>> > diff --git a/fs/ksmbd/smbacl.c b/fs/ksmbd/smbacl.c
>> > index 20455d810523..f28af33c0bd5 100644
>> > --- a/fs/ksmbd/smbacl.c
>> > +++ b/fs/ksmbd/smbacl.c
>> > @@ -1300,6 +1300,7 @@ int set_info_sec(struct ksmbd_conn *conn, struct
>> > ksmbd_tree_connect *tcon,
>> >         struct smb_fattr fattr = {{0}};
>> >         struct inode *inode = d_inode(path->dentry);
>> >         struct user_namespace *user_ns = mnt_user_ns(path->mnt);
>> > +       struct iattr newattrs;
>> >
>> >         fattr.cf_uid = INVALID_UID;
>> >         fattr.cf_gid = INVALID_GID;
>> > @@ -1309,12 +1310,28 @@ int set_info_sec(struct ksmbd_conn *conn,
>> > struct
>> > ksmbd_tree_connect *tcon,
>> >         if (rc)
>> >                 goto out;
>> >
>> > -       inode->i_mode = (inode->i_mode & ~0777) | (fattr.cf_mode &
>> > 0777);
>> > -       if (!uid_eq(fattr.cf_uid, INVALID_UID))
>> > -               inode->i_uid = fattr.cf_uid;
>> > -       if (!gid_eq(fattr.cf_gid, INVALID_GID))
>> > +       newattrs.ia_valid = ATTR_CTIME;
>> > +       if (!uid_eq(fattr.cf_uid, INVALID_UID)) {
>> > +               newattrs.ia_valid |= ATTR_UID;
>> > +               newattrs.ia_uid = fattr.cf_uid;
>> > +       }
>> > +       if (!gid_eq(fattr.cf_gid, INVALID_GID)) {
>> >                 inode->i_gid = fattr.cf_gid;
>> >
>> > This needs to be removed. If setattr_prepare() fails you will still end
>> > up with inode->i_gid changed, i.e. you're changing group ownership even
>> > if you fail the subsequent setattr_prepare().
>> Oops, My mistake, I am missing remove this line.
>> >
>> > -       mark_inode_dirty(inode);
>> > +               newattrs.ia_valid |= ATTR_GID;
>> > +               newattrs.ia_gid = fattr.cf_gid;
>> > +       }
>> > +       newattrs.ia_valid |= ATTR_MODE;
>> > +       newattrs.ia_mode = (inode->i_mode & ~0777) | (fattr.cf_mode &
>> > 0777);
>> > +       rc = setattr_prepare(user_ns, path->dentry, &newattrs);
>
> Sorry, I also forgot to mention that you need to remove this too. All of
> this is handled in the underlying filesystem's ->setattr. So this just
> needs a notify_change().
Done:)

Thanks for your review!
>