On Wed, Oct 11, 2023 at 06:29:04PM +0200, Jan Kara wrote: > On Wed 11-10-23 17:27:37, Christian Brauner wrote: > > On Wed, Oct 11, 2023 at 03:59:22PM +0200, Jan Kara wrote: > > > On Wed 11-10-23 14:27:49, Max Kellermann wrote: > > > > On Wed, Oct 11, 2023 at 2:18 PM Max Kellermann <max.kellermann@xxxxxxxxx> wrote: > > > > > But without the other filesystems. I'll resend it with just the > > > > > posix_acl.h hunk. > > > > > > > > Thinking again, I don't think this is the proper solution. This may > > > > server as a workaround so those broken filesystems don't suffer from > > > > this bug, but it's not proper. > > > > > > > > posix_acl_create() is only supposed to appy the umask if the inode > > > > supports ACLs; if not, the VFS is supposed to do it. But if the > > > > filesystem pretends to have ACL support but the kernel does not, it's > > > > really a filesystem bug. Hacking the umask code into > > > > posix_acl_create() for that inconsistent case doesn't sound right. > > > > > > > > A better workaround would be this patch: > > > > https://patchwork.kernel.org/project/linux-nfs/patch/151603744662.29035.4910161264124875658.stgit@xxxxxxxxxxxxxxxx-ag/ > > > > I submitted it more than 5 years ago, it got one positive review, but > > > > was never merged. > > > > > > > > This patch enables the VFS's umask code even if the filesystem > > > > prerents to support ACLs. This still doesn't fix the filesystem bug, > > > > but makes VFS's behavior consistent. > > > > > > OK, that solution works for me as well. I agree it seems a tad bit cleaner. > > > Christian, which one would you prefer? > > > > So it always bugged me that POSIX ACLs push umask stripping down into > > the individual filesystems but it's hard to get rid of this. And we > > tried to improve the situation during the POSIX ACL rework by > > introducing vfs_prepare_umask(). > > > > Aside from that, the problem had been that filesystems like nfs v4 > > intentionally raised SB_POSIXACL to prevent umask stripping in the VFS. > > IOW, for them SB_POSIXACL was equivalent to "don't apply any umask". > > Ah, what a hack... > > > And afaict nfs v4 has it's own thing going on how and where umasks are > > applied. However, since we now have the following commit in vfs.misc: > > > > commit f61b9bb3f8386a5e59b49bf1310f5b34f47bcef9 > > Author: Jeff Layton <jlayton@xxxxxxxxxx> > > AuthorDate: Mon Sep 11 20:25:50 2023 -0400 > > Commit: Christian Brauner <brauner@xxxxxxxxxx> > > CommitDate: Thu Sep 21 15:37:47 2023 +0200 > > > > fs: add a new SB_I_NOUMASK flag > > > > SB_POSIXACL must be set when a filesystem supports POSIX ACLs, but NFSv4 > > also sets this flag to prevent the VFS from applying the umask on > > newly-created files. NFSv4 doesn't support POSIX ACLs however, which > > causes confusion when other subsystems try to test for them. > > > > Add a new SB_I_NOUMASK flag that allows filesystems to opt-in to umask > > stripping without advertising support for POSIX ACLs. Set the new flag > > on NFSv4 instead of SB_POSIXACL. > > > > Also, move mode_strip_umask to namei.h and convert init_mknod and > > init_mkdir to use it. > > > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > Message-Id: <20230911-acl-fix-v3-1-b25315333f6c@xxxxxxxxxx> > > Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx> > > > > I think it's possible to pick up the first patch linked above: > > > > fix umask on NFS with CONFIG_FS_POSIX_ACL=n doesn't lead to any > > > > and see whether we see any regressions from this. > > > > The second patch I can't easily judge that should go through nfs if at > > all. > > > > So proposal/question: should we take the first patch into vfs.misc? > > Sounds good to me. I have checked whether some other filesystem does not > try to play similar games as NFS and it appears not although overlayfs does > seem to play some games with umasks. I think that overlayfs sets SB_POSIXACL unconditionally to ensure that the upper filesystem can decide where the umask needs to be stripped. If the upper filesystem doesn't have SB_POSIXACL then the umask will be stripped directly in e.g., vfs_create(), and vfs_tmpfile(). If it does then it will be done in the upper filesystems. So with the patch I linked above that we have in vfs.misc we should be able to change overlayfs to behave similar to NFS: diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 9f43f0d303ad..361189b676b0 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -1489,8 +1489,16 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc) sb->s_xattr = ofs->config.userxattr ? ovl_user_xattr_handlers : ovl_trusted_xattr_handlers; sb->s_fs_info = ofs; +#ifdef CONFIG_FS_POSIX_ACL sb->s_flags |= SB_POSIXACL; +#endif sb->s_iflags |= SB_I_SKIP_SYNC | SB_I_IMA_UNVERIFIABLE_SIGNATURE; + /* + * Ensure that umask handling is done by the filesystems used + * for the the upper layer instead of overlayfs as that would + * lead to unexpected results. + */ + sb->s_iflags |= SB_I_NOUMASK; err = -ENOMEM; root_dentry = ovl_get_root(sb, ctx->upper.dentry, oe); Which means that umask handling will be done by the upper filesystems just as is done right now and overlayfs can stop advertising SB_POSIXACL support on a kernel that doesn't have support for it compiled in. How does that sound?
