Patch "afs: Fix missing cursor clearance" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

afs: Fix missing cursor clearance

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
afs-fix-missing-cursor-clearance.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: David Howells <[email protected]>
Date: Tue, 6 Feb 2018 06:26:30 +0000
Subject: afs: Fix missing cursor clearance

From: David Howells <[email protected]>

commit fe4d774c847398c2a45c10a780ccfde069840793 upstream.

afs_select_fileserver() ends the address cursor it is using in the case in which we get some sort of network error and run out of addresses to iterate through, before it jumps to try the next server. This also needs to be done when the server aborts with some sort of error that means we should try the next server.

Fix this by:

(1) Move the iterate_address afs_end_cursor() call to the next_server case.

(2) End the cursor in the failed case.

(3) Make afs_end_cursor() clear the ->begun flag and ->addr pointer in the address cursor.

(4) Make afs_end_cursor() able to be called on an already cleared cursor.

Without this, something like the following oops may occur:

	AFS: Assertion failed
	18446612134397189888 == 0 is false
	0xffff88007c279f00 == 0x0 is false
	------------[ cut here ]------------
	kernel BUG at fs/afs/rotate.c:360!
	RIP: 0010:afs_select_fileserver+0x79b/0xa30 [kafs]
	Call Trace:
	 afs_statfs+0xcc/0x180 [kafs]
	 ? p9_client_statfs+0x9e/0x110 [9pnet]
	 ? _cond_resched+0x19/0x40
	 statfs_by_dentry+0x6d/0x90
	 vfs_statfs+0x1b/0xc0
	 user_statfs+0x4b/0x80
	 SYSC_statfs+0x15/0x30
	 SyS_statfs+0xe/0x10
	 entry_SYSCALL_64_fastpath+0x20/0x83

---
 fs/afs/addr_list.c |   13 ++++++++++---
 fs/afs/rotate.c    |   12 ++++++------
 2 files changed, 16 insertions(+), 9 deletions(-)

@@ -332,11 +332,18 @@ bool afs_iterate_addresses(struct afs_ad
  */
 int afs_end_cursor(struct afs_addr_cursor *ac)
 {
-	if (ac->responded && ac->index != ac->start)
-		WRITE_ONCE(ac->alist->index, ac->index);
+	struct afs_addr_list *alist;
 
-	afs_put_addrlist(ac->alist);
+	alist = ac->alist;
+	if (alist) {
+		if (ac->responded && ac->index != ac->start)
+			WRITE_ONCE(alist->index, ac->index);
+		afs_put_addrlist(alist);
+	}
+
+	ac->addr = NULL;
 	ac->alist = NULL;
+	ac->begun = false;
 	return ac->error;
 }
 

@@ -334,6 +334,7 @@ start:
 
 next_server:
 	_debug("next");
+	afs_end_cursor(&fc->ac);
 	afs_put_cb_interest(afs_v2net(vnode), fc->cbi);
 	fc->cbi = NULL;
 	fc->index++;

@@ -408,16 +409,15 @@ iterate_address:
 	/* Iterate over the current server's address list to try and find an
 	 * address on which it will respond to us.
 	 */
-	if (afs_iterate_addresses(&fc->ac)) {
-		_leave(" = t");
-		return true;
-	}
+	if (!afs_iterate_addresses(&fc->ac))
+		goto next_server;
 
-	afs_end_cursor(&fc->ac);
-	goto next_server;
+	_leave(" = t");
+	return true;
 
 failed:
 	fc->flags |= AFS_FS_CURSOR_STOP;
+	afs_end_cursor(&fc->ac);
 	_leave(" = f [failed %d]", fc->ac.error);
 	return false;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/afs-fix-missing-cursor-clearance.patch queue-4.15/afs-add-missing-afs_put_cell.patch queue-4.15/afs-need-to-clear-responded-flag-in-addr-cursor.patch queue-4.15/afs-fix-server-list-handling.patch