nfsd: fix leaked file lock with nfs exported overlayfs

nfsd and lockd call vfs_lock_file() to lock/unlock the inode
returned by locks_inode(file).

Many places in nfsd/lockd code use the inode returned by
file_inode(file) for lock manipulation. With Overlayfs, file_inode()
(the underlying inode) is not the same object as locks_inode() (the
overlay inode). This can result in "Leaked POSIX lock" messages
and eventually to a kernel crash as reported by Eddie Horng:
https://marc.info/?l=linux-unionfs&m=153086643202072&w=2

Fix all the call sites in nfsd/lockd that should use locks_inode().
This is a correctness bug that manifested when overlayfs gained
NFS export support in v4.16.

Reported-by: Eddie Horng <[e-mail]>
Tested-by: Eddie Horng <[e-mail]>
Cc: Jeff Layton <[e-mail]>
Fixes: 8383f1748829 ("ovl: wire up NFS export operations")
Cc: [e-mail]
Signed-off-by: Amir Goldstein <[e-mail]>
Signed-off-by: J. Bruce Fields <[e-mail]>

fs/lockd/clntlock.c

···
 			continue;
 		if (!rpc_cmp_addr(nlm_addr(block->b_host), addr))
 			continue;
-		if (nfs_compare_fh(NFS_FH(file_inode(fl_blocked->fl_file)) ,fh) != 0)
+		if (nfs_compare_fh(NFS_FH(locks_inode(fl_blocked->fl_file)), fh) != 0)
 			continue;
 		/* Alright, we found a lock. Set the return status
 		 * and wake up the caller

fs/lockd/clntproc.c

···
 	char *nodename = req->a_host->h_rpcclnt->cl_nodename;
 
 	nlmclnt_next_cookie(&argp->cookie);
-	memcpy(&lock->fh, NFS_FH(file_inode(fl->fl_file)), sizeof(struct nfs_fh));
+	memcpy(&lock->fh, NFS_FH(locks_inode(fl->fl_file)), sizeof(struct nfs_fh));
 	lock->caller  = nodename;
 	lock->oh.data = req->a_owner;
 	lock->oh.len  = snprintf(req->a_owner, sizeof(req->a_owner), "%u@%s",

fs/lockd/svclock.c

···
 	__be32			ret;
 
 	dprintk("lockd: nlmsvc_lock(%s/%ld, ty=%d, pi=%d, %Ld-%Ld, bl=%d)\n",
-				file_inode(file->f_file)->i_sb->s_id,
-				file_inode(file->f_file)->i_ino,
+				locks_inode(file->f_file)->i_sb->s_id,
+				locks_inode(file->f_file)->i_ino,
 				lock->fl.fl_type, lock->fl.fl_pid,
 				(long long)lock->fl.fl_start,
 				(long long)lock->fl.fl_end,
···
 	__be32			ret;
 
 	dprintk("lockd: nlmsvc_testlock(%s/%ld, ty=%d, %Ld-%Ld)\n",
-				file_inode(file->f_file)->i_sb->s_id,
-				file_inode(file->f_file)->i_ino,
+				locks_inode(file->f_file)->i_sb->s_id,
+				locks_inode(file->f_file)->i_ino,
 				lock->fl.fl_type,
 				(long long)lock->fl.fl_start,
 				(long long)lock->fl.fl_end);
···
 	int	error;
 
 	dprintk("lockd: nlmsvc_unlock(%s/%ld, pi=%d, %Ld-%Ld)\n",
-				file_inode(file->f_file)->i_sb->s_id,
-				file_inode(file->f_file)->i_ino,
+				locks_inode(file->f_file)->i_sb->s_id,
+				locks_inode(file->f_file)->i_ino,
 				lock->fl.fl_pid,
 				(long long)lock->fl.fl_start,
 				(long long)lock->fl.fl_end);
···
 	int status = 0;
 
 	dprintk("lockd: nlmsvc_cancel(%s/%ld, pi=%d, %Ld-%Ld)\n",
-				file_inode(file->f_file)->i_sb->s_id,
-				file_inode(file->f_file)->i_ino,
+				locks_inode(file->f_file)->i_sb->s_id,
+				locks_inode(file->f_file)->i_ino,
 				lock->fl.fl_pid,
 				(long long)lock->fl.fl_start,
 				(long long)lock->fl.fl_end);

fs/lockd/svcsubs.c

···
 
 static inline void nlm_debug_print_file(char *msg, struct nlm_file *file)
 {
-	struct inode *inode = file_inode(file->f_file);
+	struct inode *inode = locks_inode(file->f_file);
 
 	dprintk("lockd: %s %s/%ld\n",
 		msg, inode->i_sb->s_id, inode->i_ino);
···
 {
 	struct super_block *sb = datap;
 
-	return sb == file_inode(file->f_file)->i_sb;
+	return sb == locks_inode(file->f_file)->i_sb;
 }
 
 /**

fs/nfsd/nfs4state.c

···
 		return status;
 	}
 
-	inode = file_inode(filp);
+	inode = locks_inode(filp);
 	flctx = inode->i_flctx;
 
 	if (flctx && !list_empty_careful(&flctx->flc_posix)) {

include/linux/lockd/lockd.h

···
 
 static inline struct inode *nlmsvc_file_inode(struct nlm_file *file)
 {
-	return file_inode(file->f_file);
+	return locks_inode(file->f_file);
 }
 
 static inline int __nlm_privileged_request4(const struct sockaddr *sap)
···
 static inline int nlm_compare_locks(const struct file_lock *fl1,
 				    const struct file_lock *fl2)
 {
-	return file_inode(fl1->fl_file) == file_inode(fl2->fl_file)
+	return locks_inode(fl1->fl_file) == locks_inode(fl2->fl_file)
 	     && fl1->fl_pid   == fl2->fl_pid
 	     && fl1->fl_owner == fl2->fl_owner
 	     && fl1->fl_start == fl2->fl_start