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fs/fhandle.c: fix a race in call of has_locked_children()

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commit 1f282cdc1d upstream.

may_decode_fh() is calling has_locked_children() while holding no locks.
That's an oopsable race...

The rest of the callers are safe since they are holding namespace_sem and
are guaranteed a positive refcount on the mount in question.

Rename the current has_locked_children() to __has_locked_children(), make
it static and switch the fs/namespace.c users to it.

Make has_locked_children() a wrapper for __has_locked_children(), calling
the latter under read_seqlock_excl(&mount_lock).

Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Fixes: 620c266f39 ("fhandle: relax open_by_handle_at() permission checks")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[ Harshit: Resolved conflicts due to missing commit:
  db04662e2f ("fs: allow detached mounts in clone_private_mount()") in
  linux-6.12.y ]
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Al Viro 2025-06-01 14:23:52 -04:00 committed by Greg Kroah-Hartman
parent b9290581d2
commit 6482c3dccb
1 changed files with 14 additions and 4 deletions
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18
fs/namespace.c
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@ -2227,7 +2227,7 @@ void drop_collected_mounts(struct vfsmount *mnt)
namespace_unlock();
}
bool has_locked_children(struct mount *mnt, struct dentry *dentry)
static bool __has_locked_children(struct mount *mnt, struct dentry *dentry)
{
struct mount *child;
@ -2241,6 +2241,16 @@ bool has_locked_children(struct mount *mnt, struct dentry *dentry)
return false;
}
bool has_locked_children(struct mount *mnt, struct dentry *dentry)
{
bool res;
read_seqlock_excl(&mount_lock);
res = __has_locked_children(mnt, dentry);
read_sequnlock_excl(&mount_lock);
return res;
}
/**
* clone_private_mount - create a private clone of a path
* @path: path to clone
@ -2268,7 +2278,7 @@ struct vfsmount *clone_private_mount(const struct path *path)
return ERR_PTR(-EPERM);
}
if (has_locked_children(old_mnt, path->dentry))
if (__has_locked_children(old_mnt, path->dentry))
goto invalid;
new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
@ -2762,7 +2772,7 @@ static struct mount *__do_loopback(struct path *old_path, int recurse)
if (!check_mnt(old) && old_path->dentry->d_op != &ns_dentry_operations)
return mnt;
if (!recurse && has_locked_children(old, old_path->dentry))
if (!recurse && __has_locked_children(old, old_path->dentry))
return mnt;
if (recurse)
@ -3152,7 +3162,7 @@ static int do_set_group(struct path *from_path, struct path *to_path)
goto out;
/* From mount should not have locked children in place of To's root */
if (has_locked_children(from, to->mnt.mnt_root))
if (__has_locked_children(from, to->mnt.mnt_root))
goto out;
/* Setting sharing groups is only allowed on private mounts */