afs: Refcount the afs_call struct

A static checker warning occurs in the AFS filesystem:

	fs/afs/cmservice.c:155 SRXAFSCB_CallBack()
	error: dereferencing freed memory 'call'

due to the reply being sent before we access the server it points to.  The
act of sending the reply causes the call to be freed if an error occurs
(but not if it doesn't).

On top of this, the lifetime handling of afs_call structs is fragile
because they get passed around through workqueues without any sort of
refcounting.

Deal with the issues by:

 (1) Fix the maybe/maybe not nature of the reply sending functions with
     regards to whether they release the call struct.

 (2) Refcount the afs_call struct and sort out places that need to get/put
     references.

 (3) Pass a ref through the work queue and release (or pass on) that ref in
     the work function.  Care has to be taken because a work queue may
     already own a ref to the call.

 (4) Do the cleaning up in the put function only.

 (5) Simplify module cleanup by always incrementing afs_outstanding_calls
     whenever a call is allocated.

 (6) Set the backlog to 0 with kernel_listen() at the beginning of the
     process of closing the socket to prevent new incoming calls from
     occurring and to remove the contribution of preallocated calls from
     afs_outstanding_calls before we wait on it.

A tracepoint is also added to monitor the afs_call refcount and lifetime.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Fixes: 08e0e7c82eea: "[AF_RXRPC]: Make the in-kernel AFS filesystem use AF_RXRPC."

1 files changed, 8 insertions, 1 deletions

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index b411670..65504e2 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -66,7 +66,7 @@ enum afs_call_state {
 struct afs_call {
 	const struct afs_call_type *type;	/* type of call */
 	wait_queue_head_t	waitq;		/* processes awaiting completion */
-	struct work_struct	async_work;	/* asynchronous work processor */
+	struct work_struct	async_work;	/* async I/O processor */
 	struct work_struct	work;		/* actual work processor */
 	struct rxrpc_call	*rxcall;	/* RxRPC call handle */
 	struct key		*key;		/* security for this call */
@@ -82,6 +82,7 @@ struct afs_call {
 	pgoff_t			first;		/* first page in mapping to deal with */
 	pgoff_t			last;		/* last page in mapping to deal with */
 	size_t			offset;		/* offset into received data store */
+	atomic_t		usage;
 	enum afs_call_state	state;
 	int			error;		/* error code */
 	u32			abort_code;	/* Remote abort ID or 0 */
@@ -115,6 +116,9 @@ struct afs_call_type {
 
 	/* clean up a call */
 	void (*destructor)(struct afs_call *call);
+
+	/* Work function */
+	void (*work)(struct work_struct *work);
 };
 
 /*
@@ -591,9 +595,12 @@ extern void afs_proc_cell_remove(struct afs_cell *);
  * rxrpc.c
  */
 extern struct socket *afs_socket;
+extern atomic_t afs_outstanding_calls;
 
 extern int afs_open_socket(void);
 extern void afs_close_socket(void);
+extern void afs_put_call(struct afs_call *);
+extern int afs_queue_call_work(struct afs_call *);
 extern int afs_make_call(struct in_addr *, struct afs_call *, gfp_t, bool);
 extern struct afs_call *afs_alloc_flat_call(const struct afs_call_type *,
 					    size_t, size_t);