ceph: avoid use-after-free in ceph_fl_release_lock()

When ceph releasing the file_lock it will try to get the inode pointer
from the fl->fl_file, which the memory could already be released by
another thread in filp_close(). Because in VFS layer the fl->fl_file
doesn't increase the file's reference counter.

Will switch to use ceph dedicate lock info to track the inode.

And in ceph_fl_release_lock() we should skip all the operations if the
fl->fl_u.ceph.inode is not set, which should come from the request
file_lock. And we will set fl->fl_u.ceph.inode when inserting it to the
inode lock list, which is when copying the lock.

Link: https://tracker.ceph.com/issues/57986
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/locks.c b/fs/ceph/locks.c
index 6b3b8c299c17aec6d1611a543a45a6f230a536d1..9c8dc8a55e7e13e05fed766ea8505aa6ae9c6b62 100644 (file)
--- a/fs/ceph/locks.c
+++ b/fs/ceph/locks.c
@@ -34,18 +34,34 @@ static void ceph_fl_copy_lock(struct file_lock *dst, struct file_lock *src)
 {
        struct inode *inode = file_inode(dst->fl_file);
        atomic_inc(&ceph_inode(inode)->i_filelock_ref);
+       dst->fl_u.ceph.inode = igrab(inode);
 }
 
+/*
+ * Do not use the 'fl->fl_file' in release function, which
+ * is possibly already released by another thread.
+ */
 static void ceph_fl_release_lock(struct file_lock *fl)
 {
-       struct inode *inode = file_inode(fl->fl_file);
-       struct ceph_inode_info *ci = ceph_inode(inode);
+       struct inode *inode = fl->fl_u.ceph.inode;
+       struct ceph_inode_info *ci;
+
+       /*
+        * If inode is NULL it should be a request file_lock,
+        * nothing we can do.
+        */
+       if (!inode)
+               return;
+
+       ci = ceph_inode(inode);
        if (atomic_dec_and_test(&ci->i_filelock_ref)) {
                /* clear error when all locks are released */
                spin_lock(&ci->i_ceph_lock);
                ci->i_ceph_flags &= ~CEPH_I_ERROR_FILELOCK;
                spin_unlock(&ci->i_ceph_lock);
        }
+       fl->fl_u.ceph.inode = NULL;
+       iput(inode);
 }
 
 static const struct file_lock_operations ceph_fl_lock_ops = {

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 066555ad1bf810b7a57437cc2b3607c9ec5d52f9..c1769a2c5d7082858e3fac64b261b5e5244d9b01 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1119,6 +1119,9 @@ struct file_lock {
                        int state;              /* state of grant or error if -ve */
                        unsigned int    debug_id;
                } afs;
+               struct {
+                       struct inode *inode;
+               } ceph;
        } fl_u;
 } __randomize_layout;