Pull hostfs fix from Al Viro:
 "Fix hostfs __dentry_name() string handling.

  The use of strcpy() with overlapping source and destination is a UB;
  original loop hadn't been. More to the point, the whole thing is much
  easier done with memcpy() + memmove()"

* tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  hostfs: fix string handling in __dentry_name()

strcpy() should not be used with destination potentially overlapping
the source; what's more, strscpy() in there is pointless - we already
know the amount we want to copy; might as well use memcpy().

Fixes: c278e81b8a02 "hostfs: Remove open coded strcpy()"
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

If we add a migrate_folio operation, we can convert the writepage
operation to writepages.  The large folio support here is illusory;
we would need to kmap each page in turn for proper support.  But we do
remove a few hidden calls to compound_head().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://patch.msgid.link/20241220051500.1919389-1-willy@infradead.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

The __filemap_get_folio() function returns error pointers.
It never returns NULL. So use IS_ERR() to check it.

Fixes: 1da86618bdce ("fs: Convert aops->write_begin to take a folio")
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Richard Weinberger <richard@nod.at>

This parameter is UML specific and is unknown to kernel. It should not
be propagated to kernel, otherwise it will be passed to user space as
an environment option by kernel with a warning like:

Unknown kernel command line parameters "hostfs=/foo", will be passed to user space.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20241011040441.1586345-7-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Convert all callers from working on a page to working on one page
of a folio (support for working on an entire folio can come later).
Removes a lot of folio->page->folio conversions.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Most callers have a folio, and most implementations operate on a folio,
so remove the conversion from folio->page->folio to fit through this
interface.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Convert the passed page to a folio and operate on that.
Replaces four calls to compound_head() with one.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Pull vfs fixes from Christian Brauner:
 "This contains two fixes for this merge window:

  VFS:

   - I noticed that it is possible for a privileged user to mount most
     filesystems with a non-initial user namespace in sb->s_user_ns.

     When fsopen() is called in a non-init namespace the caller's
     namespace is recorded in fs_context->user_ns. If the returned file
     descriptor is then passed to a process privileged in init_user_ns,
     that process can call fsconfig(fd_fs, FSCONFIG_CMD_CREATE*),
     creating a new superblock with sb->s_user_ns set to the namespace
     of the process which called fsopen().

     This is problematic as only filesystems that raise FS_USERNS_MOUNT
     are known to be able to support a non-initial s_user_ns. Others may
     suffer security issues, on-disk corruption or outright crash the
     kernel. Prevent that by restricting such delegation to filesystems
     that allow FS_USERNS_MOUNT.

     Note, that this delegation requires a privileged process to
     actually create the superblock so either the privileged process is
     cooperaing or someone must have tricked a privileged process into
     operating on a fscontext file descriptor whose origin it doesn't
     know (a stupid idea).

     The bug dates back to about 5 years afaict.

  Misc:

   - Fix hostfs parsing when the mount request comes in via the legacy
     mount api.

     In the legacy mount api hostfs allows to specify the host directory
     mount without any key.

     Restore that behavior"

* tag 'vfs-6.11-rc1.fixes.3' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  hostfs: fix the host directory parse when mounting.
  fs: don't allow non-init s_user_ns for filesystems without FS_USERNS_MOUNT

hostfs not keep the host directory when mounting. When the host
directory is none (default), fc->source is used as the host root
directory, and this is wrong. Here we use `parse_monolithic` to
handle the old mount path for parsing the root directory. For new
mount path, The `parse_param` is used for the host directory parse.

Reported-and-tested-by: Maciej Żenczykowski <maze@google.com>
Fixes: cd140ce9f611 ("hostfs: convert hostfs to use the new mount API")
Link: https://lore.kernel.org/all/CANP3RGceNzwdb7w=vPf5=7BCid5HVQDmz1K5kC9JG42+HVAh_g@mail.gmail.com/
Cc: Christian Brauner <brauner@kernel.org>
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Link: https://lore.kernel.org/r/20240725065130.1821964-1-lihongbo22@huawei.com
[brauner: minor fixes]
Signed-off-by: Christian Brauner <brauner@kernel.org>