[PATCH v4 2/2] cifs: fix cifsFileInfo leak on kmalloc failure in deferred close drain paths

[Frank Sorenson <sorenson@redhat.com>]

In cifs_close_deferred_file(), cifs_close_all_deferred_files(), and
cifs_close_deferred_file_under_dentry(), when a pending deferred close
is cancelled via cancel_delayed_work(), the subsequent kmalloc_obj() to
add the file to the local processing list may fail under memory pressure.
The loop breaks immediately, but the cancelled work is no longer pending
(it would have called _cifsFileInfo_put()), and the cfile is never added
to file_head for processing.  The cifsFileInfo reference and the open
server handle both leak.

Fix by saving the cfile that failed allocation in a local variable,
breaking as before, and calling _cifsFileInfo_put() on it after
releasing the lock.  Any files later in the iteration are unaffected
since their deferred work is still pending and will fire normally.

Fixes: e3fc065682eb ("cifs: Deferred close performance improvements")
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
---
--- a/fs/smb/client/misc.c
+++ b/fs/smb/client/misc.c
@@ -497,7 +497,7 @@
 void
 cifs_close_deferred_file(struct cifsInodeInfo *cifs_inode)
 {
-	struct cifsFileInfo *cfile = NULL;
+	struct cifsFileInfo *cfile = NULL, *failed_cfile = NULL;
 	struct file_list *tmp_list, *tmp_next_list;
 	LIST_HEAD(file_head);
 
@@ -514,8 +514,10 @@
 
 				tmp_list = kmalloc_obj(struct file_list,
 						       GFP_ATOMIC);
-				if (tmp_list == NULL)
+				if (tmp_list == NULL) {
+					failed_cfile = cfile;
 					break;
+				}
 				tmp_list->cfile = cfile;
 				list_add_tail(&tmp_list->list, &file_head);
 			}
@@ -523,6 +525,15 @@
 	}
 	spin_unlock(&cifs_inode->open_file_lock);
 
+	if (failed_cfile) {
+		if (OPEN_FMODE(failed_cfile->f_flags) & FMODE_WRITE) {
+			/* Pairs with smp_load_acquire() in is_size_safe_to_change(). */
+			smp_store_release(&CIFS_I(d_inode(failed_cfile->dentry))->time_last_write,
+					  jiffies);
+		}
+		_cifsFileInfo_put(failed_cfile, false, false);
+	}
+
 	list_for_each_entry_safe(tmp_list, tmp_next_list, &file_head, list) {
 		struct cifsFileInfo *cfile = tmp_list->cfile;
 
@@ -540,7 +551,7 @@
 void
 cifs_close_all_deferred_files(struct cifs_tcon *tcon)
 {
-	struct cifsFileInfo *cfile;
+	struct cifsFileInfo *cfile, *failed_cfile = NULL;
 	struct file_list *tmp_list, *tmp_next_list;
 	LIST_HEAD(file_head);
 
@@ -554,8 +565,10 @@
 
 				tmp_list = kmalloc_obj(struct file_list,
 						       GFP_ATOMIC);
-				if (tmp_list == NULL)
+				if (tmp_list == NULL) {
+					failed_cfile = cfile;
 					break;
+				}
 				tmp_list->cfile = cfile;
 				list_add_tail(&tmp_list->list, &file_head);
 			}
@@ -563,6 +576,15 @@
 	}
 	spin_unlock(&tcon->open_file_lock);
 
+	if (failed_cfile) {
+		if (OPEN_FMODE(failed_cfile->f_flags) & FMODE_WRITE) {
+			/* Pairs with smp_load_acquire() in is_size_safe_to_change(). */
+			smp_store_release(&CIFS_I(d_inode(failed_cfile->dentry))->time_last_write,
+					  jiffies);
+		}
+		_cifsFileInfo_put(failed_cfile, true, false);
+	}
+
 	list_for_each_entry_safe(tmp_list, tmp_next_list, &file_head, list) {
 		struct cifsFileInfo *cfile = tmp_list->cfile;
 
@@ -618,7 +640,7 @@
 					   struct dentry *dentry)
 {
 	struct file_list *tmp_list, *tmp_next_list;
-	struct cifsFileInfo *cfile;
+	struct cifsFileInfo *cfile, *failed_cfile = NULL;
 	LIST_HEAD(file_head);
 
 	spin_lock(&tcon->open_file_lock);
@@ -631,14 +653,25 @@
 			spin_unlock(&CIFS_I(d_inode(cfile->dentry))->deferred_lock);
 
 			tmp_list = kmalloc_obj(struct file_list, GFP_ATOMIC);
-			if (tmp_list == NULL)
+			if (tmp_list == NULL) {
+				failed_cfile = cfile;
 				break;
+			}
 			tmp_list->cfile = cfile;
 			list_add_tail(&tmp_list->list, &file_head);
 		}
 	}
 	spin_unlock(&tcon->open_file_lock);
 
+	if (failed_cfile) {
+		if (OPEN_FMODE(failed_cfile->f_flags) & FMODE_WRITE) {
+			/* Pairs with smp_load_acquire() in is_size_safe_to_change(). */
+			smp_store_release(&CIFS_I(d_inode(failed_cfile->dentry))->time_last_write,
+					  jiffies);
+		}
+		_cifsFileInfo_put(failed_cfile, true, false);
+	}
+
 	list_for_each_entry_safe(tmp_list, tmp_next_list, &file_head, list) {
 		struct cifsFileInfo *cfile = tmp_list->cfile;
 

---
2.55.0