On Wed, Jul 27, 2022 at 09:00:46AM -0400, Jeff Layton wrote: > On Wed, 2022-07-27 at 14:32 +0200, Christian Brauner wrote: > > On Wed, Jul 27, 2022 at 08:04:34AM -0400, Jeff Layton wrote: > > > On Wed, 2022-07-27 at 13:34 +0200, Christian Brauner wrote: > > > > On Tue, Jul 26, 2022 at 04:27:56PM -0400, Jeff Layton wrote: > > > > > On Tue, 2022-07-26 at 16:23 -0400, Jeff Layton wrote: > > > > > > NFS server is exporting a sticky directory (mode 01777) with root > > > > > > squashing enabled. Client has protect_regular enabled and then tries to > > > > > > open a file as root in that directory. File is created (with ownership > > > > > > set to nobody:nobody) but the open syscall returns an error. > > > > > > > > > > > > The problem is may_create_in_sticky, which rejects the open even though > > > > > > the file has already been created/opened. Only call may_create_in_sticky > > > > > > if the file hasn't already been opened or created. > > > > > > > > > > > > Cc: Christian Brauner <brauner@xxxxxxxxxx> > > > > > > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829 > > > > > > Reported-by: Yongchen Yang <yoyang@xxxxxxxxxx> > > > > > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > > > > > --- > > > > > > fs/namei.c | 13 +++++++++---- > > > > > > 1 file changed, 9 insertions(+), 4 deletions(-) > > > > > > > > > > > > diff --git a/fs/namei.c b/fs/namei.c > > > > > > index 1f28d3f463c3..7480b6dc8d27 100644 > > > > > > --- a/fs/namei.c > > > > > > +++ b/fs/namei.c > > > > > > @@ -3495,10 +3495,15 @@ static int do_open(struct nameidata *nd, > > > > > > return -EEXIST; > > > > > > if (d_is_dir(nd->path.dentry)) > > > > > > return -EISDIR; > > > > > > - error = may_create_in_sticky(mnt_userns, nd, > > > > > > - d_backing_inode(nd->path.dentry)); > > > > > > - if (unlikely(error)) > > > > > > - return error; > > > > > > + if (!(file->f_mode & (FMODE_OPENED | FMODE_CREATED))) { > > > > > > + error = may_create_in_sticky(mnt_userns, nd, > > > > > > + d_backing_inode(nd->path.dentry)); > > > > > > + if (unlikely(error)) { > > > > > > + printk("%s: f_mode=0x%x oflag=0x%x\n", > > > > > > + __func__, file->f_mode, open_flag); > > > > > > + return error; > > > > > > + } > > > > > > + } > > > > > > } > > > > > > if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) > > > > > > return -ENOTDIR; > > > > > > > > > > I'm pretty sure this patch is the wrong approach, actually, since it > > > > > doesn't fix the regular (non-atomic) open codepath. Any thoughts on what > > > > > > > > Hey Jeff, > > > > > > > > I haven't quite understood why that won't work for the regular open > > > > codepaths. I'm probably missing something obvious. > > > > > > > > > > In the normal open codepaths, FMODE_OPENED | FMODE_CREATED are still > > > clear. If we're not doing an atomic_open (i.e. the dentry doesn't exist > > > yet or is negative), then nothing really happens until you get to the > > > vfs_open call. > > > > Hm, so for atomic open with O_CREAT it's: > > > > path_openat() > > -> open_last_lookups() > > -> lookup_open() > > /* > > * This is ->atomic_open() and FMODE_CREATED is set in the fs so > > * for NFS it's done in: > > * fs/nfs/dir.c: file->f_mode |= FMODE_CREATED; > > */ > > -> atomic_open() > > > > and for regular O_CREAT open it's: > > > > path_openat() > > -> open_last_lookups() > > -> lookup_open() > > { > > if (!dentry->d_inode && (open_flag & O_CREAT)) { > > file->f_mode |= FMODE_CREATED; > > } > > > > > > and that should all get surfaced to: > > > > path_openat() > > -> do_open() > > -> may_create_in_sticky() > > > > ? > > Basically, yes, but we also need to deal with the case where the file > already exists. That's being denied currently too and I don't think it > should be. Yeah, that's the part I'm not sure I agree with (see other thread).
