On Fri, Apr 22, 2022 at 10:13:52AM +0000, xuyang2018.jy@xxxxxxxxxxx wrote:
> on 2022/4/22 17:47, Christian Brauner wrote:
> > On Fri, Apr 22, 2022 at 06:03:09AM +0000, xuyang2018.jy@xxxxxxxxxxx wrote:
> >> on 2022/4/21 16:35, Christian Brauner wrote:
> >>> On Thu, Apr 21, 2022 at 03:54:17PM +0800, Yang Xu wrote:
> >>>> Currently, vfs only passes mode argument to filesystem, then use inode_init_owner()
> >>>> to strip S_ISGID. Some filesystem(ie ext4/btrfs) will call inode_init_owner
> >>>> firstly, then posxi acl setup, but xfs uses the contrary order. It will
> >>>> affect S_ISGID clear especially we filter S_IXGRP by umask or acl.
> >>>>
> >>>> Regardless of which filesystem is in use, failure to strip the SGID correctly
> >>>> is considered a security failure that needs to be fixed. The current VFS
> >>>> infrastructure requires the filesystem to do everything right and not step on
> >>>> any landmines to strip the SGID bit, when in fact it can easily be done at the
> >>>> VFS and the filesystems then don't even need to be aware that the SGID needs
> >>>> to be (or has been stripped) by the operation the user asked to be done.
> >>>>
> >>>> Vfs has all the info it needs - it doesn't need the filesystems to do everything
> >>>> correctly with the mode and ensuring that they order things like posix acl setup
> >>>> functions correctly with inode_init_owner() to strip the SGID bit.
> >>>>
> >>>> Just strip the SGID bit at the VFS, and then the filesystem can't get it wrong.
> >>>>
> >>>> Also, the inode_sgid_strip() api should be used before IS_POSIXACL() because
> >>>> this api may change mode.
> >>>>
> >>>> Only the following places use inode_init_owner
> >>>> "
> >>>> arch/powerpc/platforms/cell/spufs/inode.c: inode_init_owner(&init_user_ns, inode, dir, mode | S_IFDIR);
> >>>> arch/powerpc/platforms/cell/spufs/inode.c: inode_init_owner(&init_user_ns, inode, dir, mode | S_IFDIR);
> >>>> fs/9p/vfs_inode.c: inode_init_owner(&init_user_ns, inode, NULL, mode);
> >>>> fs/bfs/dir.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/btrfs/inode.c: inode_init_owner(mnt_userns, inode, dir, mode);
> >>>> fs/btrfs/tests/btrfs-tests.c: inode_init_owner(&init_user_ns, inode, NULL, S_IFREG);
> >>>> fs/ext2/ialloc.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/ext4/ialloc.c: inode_init_owner(mnt_userns, inode, dir, mode);
> >>>> fs/f2fs/namei.c: inode_init_owner(mnt_userns, inode, dir, mode);
> >>>> fs/hfsplus/inode.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/hugetlbfs/inode.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/jfs/jfs_inode.c: inode_init_owner(&init_user_ns, inode, parent, mode);
> >>>> fs/minix/bitmap.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/nilfs2/inode.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/ntfs3/inode.c: inode_init_owner(mnt_userns, inode, dir, mode);
> >>>> fs/ocfs2/dlmfs/dlmfs.c: inode_init_owner(&init_user_ns, inode, NULL, mode);
> >>>> fs/ocfs2/dlmfs/dlmfs.c: inode_init_owner(&init_user_ns, inode, parent, mode);
> >>>> fs/ocfs2/namei.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/omfs/inode.c: inode_init_owner(&init_user_ns, inode, NULL, mode);
> >>>> fs/overlayfs/dir.c: inode_init_owner(&init_user_ns, inode, dentry->d_parent->d_inode, mode);
> >>>> fs/ramfs/inode.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/reiserfs/namei.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/sysv/ialloc.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/ubifs/dir.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/udf/ialloc.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/ufs/ialloc.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> fs/xfs/xfs_inode.c: inode_init_owner(mnt_userns, inode, dir, mode);
> >>>> fs/zonefs/super.c: inode_init_owner(&init_user_ns, inode, parent, S_IFDIR | 0555);
> >>>> kernel/bpf/inode.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> mm/shmem.c: inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>> "
> >>>>
> >>>> They are used in filesystem to init new inode function and these init inode
> >>>> functions are used by following operations:
> >>>> mkdir
> >>>> symlink
> >>>> mknod
> >>>> create
> >>>> tmpfile
> >>>> rename
> >>>>
> >>>> We don't care about mkdir because we don't strip SGID bit for directory except
> >>>> fs.xfs.irix_sgid_inherit. But we even call prepare_mode() in do_mkdirat() since
> >>>> inode_sgid_strip() will skip directories anyway. This will enforce the same
> >>>> ordering for all relevant operations and it will make the code more uniform and
> >>>> easier to understand by using new helper prepare_mode().
> >>>>
> >>>> symlink and rename only use valid mode that doesn't have SGID bit.
> >>>>
> >>>> We have added inode_sgid_strip api for the remaining operations.
> >>>>
> >>>> In addition to the above six operations, four filesystems has a little difference
> >>>> 1) btrfs has btrfs_create_subvol_root to create new inode but used non SGID bit
> >>>> mode and can ignore
> >>>> 2) ocfs2 reflink function should add inode_sgid_strip api manually because we
> >>>> don't add it in vfs
> >>>> 3) spufs which doesn't really go hrough the regular VFS callpath because it has
> >>>> separate system call spu_create, but it t only allows the creation of
> >>>> directories and only allows bits in 0777 and can ignore
> >>>> 4) bpf use vfs_mkobj in bpf_obj_do_pin with
> >>>> "S_IFREG | ((S_IRUSR | S_IWUSR)& ~current_umask()) mode and
> >>>> use bpf_mkobj_ops in bpf_iter_link_pin_kernel with S_IFREG | S_IRUSR mode,
> >>>> so bpf is also not affected
> >>>>
> >>>> This patch also changed grpid behaviour for ext4/xfs because the mode passed to
> >>>> them may been changed by inode_sgid_strip.
> >>>>
> >>>> Also as Christian Brauner said"
> >>>> The patch itself is useful as it would move a security sensitive operation that is
> >>>> currently burried in individual filesystems into the vfs layer. But it has a decent
> >>>> regression potential since it might strip filesystems that have so far relied on
> >>>> getting the S_ISGID bit with a mode argument. So this needs a lot of testing and
> >>>> long exposure in -next for at least one full kernel cycle."
> >>>>
> >>>> Suggested-by: Dave Chinner<david@xxxxxxxxxxxxx>
> >>>> Signed-off-by: Yang Xu<xuyang2018.jy@xxxxxxxxxxx>
> >>>> ---
> >>>> v4->v5:
> >>>> put inode_sgid_strip before the inode_init_owner in ocfs2 filesystem
> >>>> because the inode->i_mode's assignment is in inode_init_owner
> >>>> fs/inode.c | 2 --
> >>>> fs/namei.c | 22 +++++++++-------------
> >>>> fs/ocfs2/namei.c | 1 +
> >>>> include/linux/fs.h | 11 +++++++++++
> >>>> 4 files changed, 21 insertions(+), 15 deletions(-)
> >>>>
> >>>> diff --git a/fs/inode.c b/fs/inode.c
> >>>> index 57130e4ef8b4..95667e634bd4 100644
> >>>> --- a/fs/inode.c
> >>>> +++ b/fs/inode.c
> >>>> @@ -2246,8 +2246,6 @@ void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode,
> >>>> /* Directories are special, and always inherit S_ISGID */
> >>>> if (S_ISDIR(mode))
> >>>> mode |= S_ISGID;
> >>>> - else
> >>>> - mode = inode_sgid_strip(mnt_userns, dir, mode);
> >>>> } else
> >>>> inode_fsgid_set(inode, mnt_userns);
> >>>> inode->i_mode = mode;
> >>>> diff --git a/fs/namei.c b/fs/namei.c
> >>>> index 73646e28fae0..5b8e6288d503 100644
> >>>> --- a/fs/namei.c
> >>>> +++ b/fs/namei.c
> >>>> @@ -3287,8 +3287,7 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
> >>>> if (open_flag& O_CREAT) {
> >>>> if (open_flag& O_EXCL)
> >>>> open_flag&= ~O_TRUNC;
> >>>> - if (!IS_POSIXACL(dir->d_inode))
> >>>> - mode&= ~current_umask();
> >>>> + mode = prepare_mode(mnt_userns, dir->d_inode, mode);
> >>>> if (likely(got_write))
> >>>> create_error = may_o_create(mnt_userns,&nd->path,
> >>>> dentry, mode);
> >>>> @@ -3521,8 +3520,7 @@ struct dentry *vfs_tmpfile(struct user_namespace *mnt_userns,
> >>>> child = d_alloc(dentry,&slash_name);
> >>>> if (unlikely(!child))
> >>>> goto out_err;
> >>>> - if (!IS_POSIXACL(dir))
> >>>> - mode&= ~current_umask();
> >>>> + mode = prepare_mode(mnt_userns, dir, mode);
> >>>> error = dir->i_op->tmpfile(mnt_userns, dir, child, mode);
> >>>> if (error)
> >>>> goto out_err;
> >>>> @@ -3850,13 +3848,12 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode,
> >>>> if (IS_ERR(dentry))
> >>>> goto out1;
> >>>>
> >>>> - if (!IS_POSIXACL(path.dentry->d_inode))
> >>>> - mode&= ~current_umask();
> >>>> + mnt_userns = mnt_user_ns(path.mnt);
> >>>> + mode = prepare_mode(mnt_userns, path.dentry->d_inode, mode);
> >>>> error = security_path_mknod(&path, dentry, mode, dev);
> >>>> if (error)
> >>>> goto out2;
> >>>>
> >>>> - mnt_userns = mnt_user_ns(path.mnt);
> >>>> switch (mode& S_IFMT) {
> >>>> case 0: case S_IFREG:
> >>>> error = vfs_create(mnt_userns, path.dentry->d_inode,
> >>>> @@ -3943,6 +3940,7 @@ int do_mkdirat(int dfd, struct filename *name, umode_t mode)
> >>>> struct path path;
> >>>> int error;
> >>>> unsigned int lookup_flags = LOOKUP_DIRECTORY;
> >>>> + struct user_namespace *mnt_userns;
> >>>>
> >>>> retry:
> >>>> dentry = filename_create(dfd, name,&path, lookup_flags);
> >>>> @@ -3950,15 +3948,13 @@ int do_mkdirat(int dfd, struct filename *name, umode_t mode)
> >>>> if (IS_ERR(dentry))
> >>>> goto out_putname;
> >>>>
> >>>> - if (!IS_POSIXACL(path.dentry->d_inode))
> >>>> - mode&= ~current_umask();
> >>>> + mnt_userns = mnt_user_ns(path.mnt);
> >>>> + mode = prepare_mode(mnt_userns, path.dentry->d_inode, mode);
> >>>> error = security_path_mkdir(&path, dentry, mode);
> >>>> - if (!error) {
> >>>> - struct user_namespace *mnt_userns;
> >>>> - mnt_userns = mnt_user_ns(path.mnt);
> >>>> + if (!error)
> >>>> error = vfs_mkdir(mnt_userns, path.dentry->d_inode, dentry,
> >>>> mode);
> >>>> - }
> >>>> +
> >>>> done_path_create(&path, dentry);
> >>>> if (retry_estale(error, lookup_flags)) {
> >>>> lookup_flags |= LOOKUP_REVAL;
> >>>> diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
> >>>> index c75fd54b9185..21f3da2e66c9 100644
> >>>> --- a/fs/ocfs2/namei.c
> >>>> +++ b/fs/ocfs2/namei.c
> >>>> @@ -197,6 +197,7 @@ static struct inode *ocfs2_get_init_inode(struct inode *dir, umode_t mode)
> >>>> * callers. */
> >>>> if (S_ISDIR(mode))
> >>>> set_nlink(inode, 2);
> >>>> + mode = inode_sgid_strip(&init_user_ns, dir, mode);
> >>>> inode_init_owner(&init_user_ns, inode, dir, mode);
> >>>
> >>> For the record, I'm not too fond of this separate invocation of
> >>> inode_sgid_strip() but since it's only one location this might be fine.
> >>> If there's more than one location a separate helper should exist for
> >>> this that abstracts this away for the filesystem.
> >> Agree. This case only be found when using OCFS2_IOC_REFLINK ioctl. And
> >
> > (I have one very minor non-technical ask: can you please make sure to
> > leave an empty line between the text you're citing and your reply? It
> > would make reading your replies a lot easier. :))
>
> Of course.
>
> >
> >> other support reflink filesystem(xfs, btrfs) they use FICLONE or
> >> FICLONERANGE ioctl.
> >>
> >> Since ocfs2 has supported reflink by using it remap_file_range, should
> >> we still need this ioctl?
> >>
> >> commit bd50873dc725a9fa72592ecc986c58805e823051
> >> Author: Tao Ma<tao.ma@xxxxxxxxxx>
> >> Date: Mon Sep 21 11:25:14 2009 +0800
> >>
> >> ocfs2: Add ioctl for reflink.
> >>
> >> The ioctl will take 3 parameters: old_path, new_path and
> >> preserve and call vfs_reflink. It is useful when we backport
> >> reflink features to old kernels.
> >>
> >> Signed-off-by: Tao Ma<tao.ma@xxxxxxxxxx>
> >>
> >> Of course, this is a problem doesn't belong to this series.
> >>
> >>>
> >>> Two questions:
> >>> - Sould this call prepare_mode(), i.e. should we honor umasks here too?
> >> IMO, it desn't need to honor umask. Because reflink only will update
> >> inode_imode by setattr to strip S_ISGID and S_ISUID instead of creating
> >> a file.
> >
> > I had a misconception here because I got confused by ocfs2.
> > While the OCFS2_IOC_REFLINK ioctl creates the target file itself and the
> > reflink the FICLONE and FICLONERANGE _only_ create the reflink.
> >
> > So the target file itself must've been created prior to
> > FICLONE/FICLONERANGE which means basic setgid stripping should've been
> > done when the file was created.
>
> Yes.
>
> >
> > Since ocfs2 reflink callpaths work very differently we can't switch it
> > to FICLONE/FICLONERANGE as this would regress ocfs2 users.
> >
> >>> - How is the sgid bit handled when creating reflinks on other reflink
> >>> supporting filesystems such as xfs and btrfs?
> >> xfstests has a test case generic/673 for this, so btrfs and xfs should
> >> have the same behavior.
> >> I look into xfs code.
> >>
> >> Firstly
> >>
> >> If we don't have CAP_FSETID and it is a regulre file,also have sgid bit,
> >> then should_remove_suid will give attr a ATTR_KILL_SGID mask.
> >
> > What you're referring to below is privilege stripping when _modifying
> > the content_ of set{g,u}id binaries.
> >
> > That happens e.g. during write() or indeed a reflink creation via
> > FICLONE/FICLONERANGE. For the latter privilege stripping happens when
> > only some extents are reflinked and not the whole file. So that's:
> >
> > * ioctl_file_clone()
> > * vfs_clone_file_range()
> > * do_clone_file_range()
> > * generic_file_rw_checks()
> > * remap_verify_area()
> > * security_file_permission()
> > * ->remap_file_range() [1]
> >
> > [1]:
> > btrfs:
> > * btrfs_remap_file_range()
> > * generic_remap_file_range_prep()
> > * file_modified() // privilege stripping
> >
> > ocfs2:
> > * ocfs2_remap_file_range()
> > * generic_remap_file_range_prep()
> > * file_modified() // privilege stripping
> >
> > xfs:
> > * xfs_remap_file_range()
> > * generic_remap_file_range_prep()
> > * file_modified() // privilege stripping
> >
> > // This is stacked, i.e. ovl filesystems will rely on the filesystem
> > // used for the upper mount and it's .remap_file_range() implementation.
> > overlayfs:
> > * ovl_remap_file_range()
> > * vfs_clone_file_range()
> >
> > The other two implementers are:
> >
> > cifs:
> > * cifs_remap_file_range()
> >
> > nfs:
> > * nfs42_remap_file_range()
> >
> > both of which don't call into generic_remap_file_range_prep() and so
> > file_modified() isn't called. But they are netfses and there's a server
> > involved. In general, this isn't really a concern for this patchset.
> > (But something to potentially to look into in the future.)
> >
> > And it wasn't what I was worried about.
> >
> > The crucial information that we needed was whether reflink callpaths
> > other than ocfs2 create files themselves and therefore might rely
> > implicitly on setgid stripping in inode_init_owner().
> >
> > Now that we looked at all callers we can be confident that this isn't
> > the case. _Apart from ocfs2_ but which you handle in the patchset.
>
> If I understand correctly, this stripping code is ok. So can I send a v6
> patch?
Yes.
