| Message ID | 1649923039-2273-2-git-send-email-xuyang2018.jy@fujitsu.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2,1/3] vfs: Add inode_sgid_strip() api | expand |
On Thu, Apr 14, 2022 at 03:57:18PM +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 > "hugetlbfs/inode.c:846: inode_init_owner(&init_user_ns, inode, dir, mode); > nilfs2/inode.c:354: inode_init_owner(&init_user_ns, inode, dir, mode); > zonefs/super.c:1289: inode_init_owner(&init_user_ns, inode, parent, S_IFDIR | 0555); > reiserfs/namei.c:619: inode_init_owner(&init_user_ns, inode, dir, mode); > jfs/jfs_inode.c:67: inode_init_owner(&init_user_ns, inode, parent, mode); > f2fs/namei.c:50: inode_init_owner(mnt_userns, inode, dir, mode); > ext2/ialloc.c:549: inode_init_owner(&init_user_ns, inode, dir, mode); > overlayfs/dir.c:643: inode_init_owner(&init_user_ns, inode, dentry->d_parent->d_inode, mode); > ufs/ialloc.c:292: inode_init_owner(&init_user_ns, inode, dir, mode); > ntfs3/inode.c:1283: inode_init_owner(mnt_userns, inode, dir, mode); > ramfs/inode.c:64: inode_init_owner(&init_user_ns, inode, dir, mode); > 9p/vfs_inode.c:263: inode_init_owner(&init_user_ns, inode, NULL, mode); > btrfs/tests/btrfs-tests.c:65: inode_init_owner(&init_user_ns, inode, NULL, S_IFREG); > btrfs/inode.c:6215: inode_init_owner(mnt_userns, inode, dir, mode); > sysv/ialloc.c:166: inode_init_owner(&init_user_ns, inode, dir, mode); > omfs/inode.c:51: inode_init_owner(&init_user_ns, inode, NULL, mode); > ubifs/dir.c:97: inode_init_owner(&init_user_ns, inode, dir, mode); > udf/ialloc.c:108: inode_init_owner(&init_user_ns, inode, dir, mode); > ext4/ialloc.c:979: inode_init_owner(mnt_userns, inode, dir, mode); > hfsplus/inode.c:393: inode_init_owner(&init_user_ns, inode, dir, mode); > xfs/xfs_inode.c:840: inode_init_owner(mnt_userns, inode, dir, mode); > ocfs2/dlmfs/dlmfs.c:331: inode_init_owner(&init_user_ns, inode, NULL, mode); > ocfs2/dlmfs/dlmfs.c:354: inode_init_owner(&init_user_ns, inode, parent, mode); > ocfs2/namei.c:200: inode_init_owner(&init_user_ns, inode, dir, mode); > minix/bitmap.c:255: inode_init_owner(&init_user_ns, inode, dir, mode); > bfs/dir.c:99: inode_init_owner(&init_user_ns, inode, dir, mode); > " For completeness sake, there's also spufs which doesn't really go through the regular VFS callpath because it has separate system calls like: SYSCALL_DEFINE4(spu_create, const char __user *, name, unsigned int, flags, umode_t, mode, int, neighbor_fd) but looking through the code it only allows the creation of directories and only allows bits in 0777. > > 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. > 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, two 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 > > Last but not least, this patch also changed grpid behaviour for ext4/xfs because the mode passed to > them may been changed by inode_sgid_strip. I think 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 trip filesystems that have so far relied on getting the S_ISGID bit with a mode argument. The example being network filesystems that Jeff brought up earlier. So this needs a lot of testing and long exposure in -next for at least one full kernel cycle imho. > > Suggested-by: Dave Chinner <david@fromorbit.com> > Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com> > --- > fs/inode.c | 4 ---- > fs/namei.c | 5 ++++- > fs/ocfs2/namei.c | 1 + > 3 files changed, 5 insertions(+), 5 deletions(-) > > diff --git a/fs/inode.c b/fs/inode.c > index d63264998855..b08bdd73e116 100644 > --- a/fs/inode.c > +++ b/fs/inode.c > @@ -2246,10 +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 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) && > - !in_group_p(i_gid_into_mnt(mnt_userns, dir)) && > - !capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID)) > - mode &= ~S_ISGID; > } else > inode_fsgid_set(inode, mnt_userns); > inode->i_mode = mode; > diff --git a/fs/namei.c b/fs/namei.c > index 3f1829b3ab5b..e03f7defdd30 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -3287,6 +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; > + inode_sgid_strip(mnt_userns, dir->d_inode, &mode); > if (!IS_POSIXACL(dir->d_inode)) > mode &= ~current_umask(); > if (likely(got_write)) > @@ -3521,6 +3522,7 @@ struct dentry *vfs_tmpfile(struct user_namespace *mnt_userns, > child = d_alloc(dentry, &slash_name); > if (unlikely(!child)) > goto out_err; > + inode_sgid_strip(mnt_userns, dir, &mode); Hm, an additional question: how is umask stripping currently handled in vfs_tmpfile()? I don't see it anywhere. That seems like a bug? > error = dir->i_op->tmpfile(mnt_userns, dir, child, mode); > if (error) > goto out_err; > @@ -3850,13 +3852,14 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode, > if (IS_ERR(dentry)) > goto out1; > > + mnt_userns = mnt_user_ns(path.mnt); > + inode_sgid_strip(mnt_userns, path.dentry->d_inode, &mode); > if (!IS_POSIXACL(path.dentry->d_inode)) > mode &= ~current_umask(); It would be worth to add another helper prepare_mode() that calls inode_sgid_strip() and does the umask stripping as well and then call it in all these places. You should 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. > 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, > diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c > index c75fd54b9185..f1d626697302 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); > + inode_sgid_strip(&init_user_ns, dir, &mode); > inode_init_owner(&init_user_ns, inode, dir, mode); > status = dquot_initialize(inode); > if (status) > -- > 2.27.0 > >
On Fri, Apr 15, 2022 at 03:14:53AM +0000, xuyang2018.jy@fujitsu.com wrote: > on 2022/4/14 20:45, Christian Brauner wrote: > > On Thu, Apr 14, 2022 at 03:57:18PM +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 > >> "hugetlbfs/inode.c:846: inode_init_owner(&init_user_ns, inode, dir, mode); > >> nilfs2/inode.c:354: inode_init_owner(&init_user_ns, inode, dir, mode); > >> zonefs/super.c:1289: inode_init_owner(&init_user_ns, inode, parent, S_IFDIR | 0555); > >> reiserfs/namei.c:619: inode_init_owner(&init_user_ns, inode, dir, mode); > >> jfs/jfs_inode.c:67: inode_init_owner(&init_user_ns, inode, parent, mode); > >> f2fs/namei.c:50: inode_init_owner(mnt_userns, inode, dir, mode); > >> ext2/ialloc.c:549: inode_init_owner(&init_user_ns, inode, dir, mode); > >> overlayfs/dir.c:643: inode_init_owner(&init_user_ns, inode, dentry->d_parent->d_inode, mode); > >> ufs/ialloc.c:292: inode_init_owner(&init_user_ns, inode, dir, mode); > >> ntfs3/inode.c:1283: inode_init_owner(mnt_userns, inode, dir, mode); > >> ramfs/inode.c:64: inode_init_owner(&init_user_ns, inode, dir, mode); > >> 9p/vfs_inode.c:263: inode_init_owner(&init_user_ns, inode, NULL, mode); > >> btrfs/tests/btrfs-tests.c:65: inode_init_owner(&init_user_ns, inode, NULL, S_IFREG); > >> btrfs/inode.c:6215: inode_init_owner(mnt_userns, inode, dir, mode); > >> sysv/ialloc.c:166: inode_init_owner(&init_user_ns, inode, dir, mode); > >> omfs/inode.c:51: inode_init_owner(&init_user_ns, inode, NULL, mode); > >> ubifs/dir.c:97: inode_init_owner(&init_user_ns, inode, dir, mode); > >> udf/ialloc.c:108: inode_init_owner(&init_user_ns, inode, dir, mode); > >> ext4/ialloc.c:979: inode_init_owner(mnt_userns, inode, dir, mode); > >> hfsplus/inode.c:393: inode_init_owner(&init_user_ns, inode, dir, mode); > >> xfs/xfs_inode.c:840: inode_init_owner(mnt_userns, inode, dir, mode); > >> ocfs2/dlmfs/dlmfs.c:331: inode_init_owner(&init_user_ns, inode, NULL, mode); > >> ocfs2/dlmfs/dlmfs.c:354: inode_init_owner(&init_user_ns, inode, parent, mode); > >> ocfs2/namei.c:200: inode_init_owner(&init_user_ns, inode, dir, mode); > >> minix/bitmap.c:255: inode_init_owner(&init_user_ns, inode, dir, mode); > >> bfs/dir.c:99: inode_init_owner(&init_user_ns, inode, dir, mode); > >> " > > > > For completeness sake, there's also spufs which doesn't really go > > through the regular VFS callpath because it has separate system calls > > like: > > > > SYSCALL_DEFINE4(spu_create, const char __user *, name, unsigned int, flags, > > umode_t, mode, int, neighbor_fd) > > > > but looking through the code it only allows the creation of directories and only > > allows bits in 0777. > IMO, this fs also doesn't use inode_init_owner, so it should be not > affected. We add indo_sgid_strip into vfs, IMO, it only happen new sgid > strip situation and doesn't happen to remove old sgid strip situation. > So I think it is "safe". It does. The callchain spu_create() with SP_CREATE_GANG ends up in spufs_mkgang() which calls inode_init_owner(). But as I said it's not a problem since this only creates directories anyway.
On Fri, Apr 15, 2022 at 09:06:25AM +0000, xuyang2018.jy@fujitsu.com wrote: > on 2022/4/15 12:15, Yang Xu wrote: > > on 2022/4/14 20:45, Christian Brauner wrote: > >> On Thu, Apr 14, 2022 at 03:57:18PM +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 > >>> "hugetlbfs/inode.c:846: inode_init_owner(&init_user_ns, inode, dir, > >>> mode); > >>> nilfs2/inode.c:354: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> zonefs/super.c:1289: inode_init_owner(&init_user_ns, inode, parent, > >>> S_IFDIR | 0555); > >>> reiserfs/namei.c:619: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> jfs/jfs_inode.c:67: inode_init_owner(&init_user_ns, inode, parent, > >>> mode); > >>> f2fs/namei.c:50: inode_init_owner(mnt_userns, inode, dir, mode); > >>> ext2/ialloc.c:549: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> overlayfs/dir.c:643: inode_init_owner(&init_user_ns, inode, > >>> dentry->d_parent->d_inode, mode); > >>> ufs/ialloc.c:292: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> ntfs3/inode.c:1283: inode_init_owner(mnt_userns, inode, dir, mode); > >>> ramfs/inode.c:64: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> 9p/vfs_inode.c:263: inode_init_owner(&init_user_ns, inode, NULL, mode); > >>> btrfs/tests/btrfs-tests.c:65: inode_init_owner(&init_user_ns, inode, > >>> NULL, S_IFREG); > >>> btrfs/inode.c:6215: inode_init_owner(mnt_userns, inode, dir, mode); > >>> sysv/ialloc.c:166: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> omfs/inode.c:51: inode_init_owner(&init_user_ns, inode, NULL, mode); > >>> ubifs/dir.c:97: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> udf/ialloc.c:108: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> ext4/ialloc.c:979: inode_init_owner(mnt_userns, inode, dir, mode); > >>> hfsplus/inode.c:393: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> xfs/xfs_inode.c:840: inode_init_owner(mnt_userns, inode, dir, mode); > >>> ocfs2/dlmfs/dlmfs.c:331: inode_init_owner(&init_user_ns, inode, NULL, > >>> mode); > >>> ocfs2/dlmfs/dlmfs.c:354: inode_init_owner(&init_user_ns, inode, > >>> parent, mode); > >>> ocfs2/namei.c:200: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> minix/bitmap.c:255: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> bfs/dir.c:99: inode_init_owner(&init_user_ns, inode, dir, mode); > >>> " > >> > >> For completeness sake, there's also spufs which doesn't really go > >> through the regular VFS callpath because it has separate system calls > >> like: > >> > >> SYSCALL_DEFINE4(spu_create, const char __user *, name, unsigned int, > >> flags, > >> umode_t, mode, int, neighbor_fd) > >> > >> but looking through the code it only allows the creation of > >> directories and only > >> allows bits in 0777. > > IMO, this fs also doesn't use inode_init_owner, so it should be not > > affected. We add indo_sgid_strip into vfs, IMO, it only happen new sgid > > strip situation and doesn't happen to remove old sgid strip situation. > > So I think it is "safe". > >> > >>> > >>> 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. > >>> 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, two 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 > >>> > >>> Last but not least, this patch also changed grpid behaviour for > >>> ext4/xfs because the mode passed to > >>> them may been changed by inode_sgid_strip. > >> > >> I think 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 trip > >> filesystems that have so far relied on getting the S_ISGID bit with a > >> mode argument. The example being network filesystems that Jeff brought > >> up earlier. So this needs a lot of testing and long exposure in -next > >> for at least one full kernel cycle imho. > > Agreed. > >> > >>> > >>> Suggested-by: Dave Chinner<david@fromorbit.com> > >>> Signed-off-by: Yang Xu<xuyang2018.jy@fujitsu.com> > >>> --- > >>> fs/inode.c | 4 ---- > >>> fs/namei.c | 5 ++++- > >>> fs/ocfs2/namei.c | 1 + > >>> 3 files changed, 5 insertions(+), 5 deletions(-) > >>> > >>> diff --git a/fs/inode.c b/fs/inode.c > >>> index d63264998855..b08bdd73e116 100644 > >>> --- a/fs/inode.c > >>> +++ b/fs/inode.c > >>> @@ -2246,10 +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 if ((mode& (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)&& > >>> - !in_group_p(i_gid_into_mnt(mnt_userns, dir))&& > >>> - !capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID)) > >>> - mode&= ~S_ISGID; > >>> } else > >>> inode_fsgid_set(inode, mnt_userns); > >>> inode->i_mode = mode; > >>> diff --git a/fs/namei.c b/fs/namei.c > >>> index 3f1829b3ab5b..e03f7defdd30 100644 > >>> --- a/fs/namei.c > >>> +++ b/fs/namei.c > >>> @@ -3287,6 +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; > >>> + inode_sgid_strip(mnt_userns, dir->d_inode,&mode); > >>> if (!IS_POSIXACL(dir->d_inode)) > >>> mode&= ~current_umask(); > >>> if (likely(got_write)) > >>> @@ -3521,6 +3522,7 @@ struct dentry *vfs_tmpfile(struct > >>> user_namespace *mnt_userns, > >>> child = d_alloc(dentry,&slash_name); > >>> if (unlikely(!child)) > >>> goto out_err; > >>> + inode_sgid_strip(mnt_userns, dir,&mode); > >> > >> Hm, an additional question: how is umask stripping currently handled in > >> vfs_tmpfile()? I don't see it anywhere. That seems like a bug? > > Yes, I think it is a bug. > Since you found this bug and I have finished my v3 kernel patch set(also > fix this tmpfile umask problem and add your reported-by, also two > patches about other problem in xfs/nfs ), so do you will fix this kernel > bug or I send a v3 directly? You can fix it as part of your series and I see you've already included it in v3 anyway.
diff --git a/fs/inode.c b/fs/inode.c index d63264998855..b08bdd73e116 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -2246,10 +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 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) && - !in_group_p(i_gid_into_mnt(mnt_userns, dir)) && - !capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID)) - mode &= ~S_ISGID; } else inode_fsgid_set(inode, mnt_userns); inode->i_mode = mode; diff --git a/fs/namei.c b/fs/namei.c index 3f1829b3ab5b..e03f7defdd30 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -3287,6 +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; + inode_sgid_strip(mnt_userns, dir->d_inode, &mode); if (!IS_POSIXACL(dir->d_inode)) mode &= ~current_umask(); if (likely(got_write)) @@ -3521,6 +3522,7 @@ struct dentry *vfs_tmpfile(struct user_namespace *mnt_userns, child = d_alloc(dentry, &slash_name); if (unlikely(!child)) goto out_err; + inode_sgid_strip(mnt_userns, dir, &mode); error = dir->i_op->tmpfile(mnt_userns, dir, child, mode); if (error) goto out_err; @@ -3850,13 +3852,14 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode, if (IS_ERR(dentry)) goto out1; + mnt_userns = mnt_user_ns(path.mnt); + inode_sgid_strip(mnt_userns, path.dentry->d_inode, &mode); if (!IS_POSIXACL(path.dentry->d_inode)) mode &= ~current_umask(); 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, diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c index c75fd54b9185..f1d626697302 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); + inode_sgid_strip(&init_user_ns, dir, &mode); inode_init_owner(&init_user_ns, inode, dir, mode); status = dquot_initialize(inode); if (status)
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 "hugetlbfs/inode.c:846: inode_init_owner(&init_user_ns, inode, dir, mode); nilfs2/inode.c:354: inode_init_owner(&init_user_ns, inode, dir, mode); zonefs/super.c:1289: inode_init_owner(&init_user_ns, inode, parent, S_IFDIR | 0555); reiserfs/namei.c:619: inode_init_owner(&init_user_ns, inode, dir, mode); jfs/jfs_inode.c:67: inode_init_owner(&init_user_ns, inode, parent, mode); f2fs/namei.c:50: inode_init_owner(mnt_userns, inode, dir, mode); ext2/ialloc.c:549: inode_init_owner(&init_user_ns, inode, dir, mode); overlayfs/dir.c:643: inode_init_owner(&init_user_ns, inode, dentry->d_parent->d_inode, mode); ufs/ialloc.c:292: inode_init_owner(&init_user_ns, inode, dir, mode); ntfs3/inode.c:1283: inode_init_owner(mnt_userns, inode, dir, mode); ramfs/inode.c:64: inode_init_owner(&init_user_ns, inode, dir, mode); 9p/vfs_inode.c:263: inode_init_owner(&init_user_ns, inode, NULL, mode); btrfs/tests/btrfs-tests.c:65: inode_init_owner(&init_user_ns, inode, NULL, S_IFREG); btrfs/inode.c:6215: inode_init_owner(mnt_userns, inode, dir, mode); sysv/ialloc.c:166: inode_init_owner(&init_user_ns, inode, dir, mode); omfs/inode.c:51: inode_init_owner(&init_user_ns, inode, NULL, mode); ubifs/dir.c:97: inode_init_owner(&init_user_ns, inode, dir, mode); udf/ialloc.c:108: inode_init_owner(&init_user_ns, inode, dir, mode); ext4/ialloc.c:979: inode_init_owner(mnt_userns, inode, dir, mode); hfsplus/inode.c:393: inode_init_owner(&init_user_ns, inode, dir, mode); xfs/xfs_inode.c:840: inode_init_owner(mnt_userns, inode, dir, mode); ocfs2/dlmfs/dlmfs.c:331: inode_init_owner(&init_user_ns, inode, NULL, mode); ocfs2/dlmfs/dlmfs.c:354: inode_init_owner(&init_user_ns, inode, parent, mode); ocfs2/namei.c:200: inode_init_owner(&init_user_ns, inode, dir, mode); minix/bitmap.c:255: inode_init_owner(&init_user_ns, inode, dir, mode); bfs/dir.c:99: 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. 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, two 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 Last but not least, this patch also changed grpid behaviour for ext4/xfs because the mode passed to them may been changed by inode_sgid_strip. Suggested-by: Dave Chinner <david@fromorbit.com> Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com> --- fs/inode.c | 4 ---- fs/namei.c | 5 ++++- fs/ocfs2/namei.c | 1 + 3 files changed, 5 insertions(+), 5 deletions(-)