| Message ID | 1650368834-2420-7-git-send-email-xuyang2018.jy@fujitsu.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4,1/8] fs: move sgid strip operation from inode_init_owner into inode_sgid_strip | expand |
On Tue, Apr 19, 2022 at 07:47:13PM +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 filesystems 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 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 it 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; , 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@fromorbit.com> > Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com> > --- I think we're getting closer but please focus the patch series. This has morphed into an 8 patch series where 4 or 5 of these patches are fixes that a) I'm not sure are worth it or fix anything b) they are filesystem specific and can be independently upstreamed and c) have nothing to do with the core of this patch series. So I'd suggest you'd just make this about sgid stripping and then this doesn't have to be more than 3 maybe 4 patches, imho.
on 2022/4/19 22:09, Christian Brauner wrote: > On Tue, Apr 19, 2022 at 07:47:13PM +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 filesystems 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 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 it 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; , 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@fromorbit.com> >> Signed-off-by: Yang Xu<xuyang2018.jy@fujitsu.com> >> --- > > I think we're getting closer but please focus the patch series. This has > morphed into an 8 patch series where 4 or 5 of these patches are fixes > that a) I'm not sure are worth it or fix anything b) they are filesystem > specific and can be independently upstreamed and c) have nothing to do > with the core of this patch series. > > So I'd suggest you'd just make this about sgid stripping and then this > doesn't have to be more than 3 maybe 4 patches, imho. Ok, will focus on this sgid stripping.
diff --git a/fs/inode.c b/fs/inode.c index 3215e61a0021..0eb1dab99893 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 - 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..f86614ab841f 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(); + 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(); + 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); + 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); + 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..c81b8e0847aa 100644 --- a/fs/ocfs2/namei.c +++ b/fs/ocfs2/namei.c @@ -198,6 +198,7 @@ static struct inode *ocfs2_get_init_inode(struct inode *dir, umode_t mode) if (S_ISDIR(mode)) set_nlink(inode, 2); inode_init_owner(&init_user_ns, inode, dir, mode); + inode_sgid_strip(&init_user_ns, dir, &mode); status = dquot_initialize(inode); if (status) return ERR_PTR(status); diff --git a/include/linux/fs.h b/include/linux/fs.h index 4a617aaab6f6..8c2f4cde974b 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -3458,6 +3458,15 @@ static inline bool dir_relax_shared(struct inode *inode) return !IS_DEADDIR(inode); } +static inline void prepare_mode(struct user_namespace *mnt_userns, + const struct inode *dir, umode_t *mode) +{ + inode_sgid_strip(mnt_userns, dir, mode); + + if (!IS_POSIXACL(dir)) + *mode &= ~current_umask(); +} + extern bool path_noexec(const struct path *path); extern void inode_nohighmem(struct inode *inode);
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 filesystems 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 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 it 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; , 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@fromorbit.com> Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com> --- fs/inode.c | 2 -- fs/namei.c | 22 +++++++++------------- fs/ocfs2/namei.c | 1 + include/linux/fs.h | 9 +++++++++ 4 files changed, 19 insertions(+), 15 deletions(-)