linux-kernel - [PATCH] Fix potential OOPS in generic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <46F233E0.4090206@openvz.org>
Date:	Thu, 20 Sep 2007 12:48:32 +0400
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	Andrew Morton <akpm@...l.org>
CC:	"J. Bruce Fields" <bfields@...ldses.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...nvz.org
Subject: [PATCH] Fix potential OOPS in generic_setlease() (v2)

This code is run under lock_kernel(), which is dropped during
sleeping operations, so the following race is possible:

CPU1:                                CPU2:
  vfs_setlease();                    vfs_setlease();
  lock_kernel();
                                     lock_kernel(); /* spin */
  generic_setlease():
    ...
    for (before = ...)
    /* here we found some lease after
     * which we will insert the new one
     */
    fl = locks_alloc_lock();
    /* go to sleep in this allocation and
     * drop the BKL
     */
                                     generic_setlease():
                                       ...
                                       for (before = ...)
                                       /* here we find the "before" pointing
                                        * at the one we found on CPU1
                                        */
                                      ->fl_change(my_before, arg);
                                              lease_modify();
                                                     locks_free_lock();
                                                     /* and we freed it */
                                     ...
                                     unlock_kernel();
   locks_insert_lock(before, fl);
   /* OOPS! We have just tried to add the lease
    * at the tail of already removed one
    */

The similar races are already handled in other code - all the 
allocations are performed before any checks/updates.

Fixed the problem, spotted by J. Bruce Fields, about the fl
variable reuse.

Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>

---

diff --git a/fs/locks.c b/fs/locks.c
index a1c1c01..d5b9653 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1354,6 +1354,7 @@ int fcntl_getlease(struct file *filp)
 int generic_setlease(struct file *filp, long arg, struct file_lock **flp)
 {
 	struct file_lock *fl, **before, **my_before = NULL, *lease;
+	struct file_lock *new_fl = NULL;
 	struct dentry *dentry = filp->f_path.dentry;
 	struct inode *inode = dentry->d_inode;
 	int error, rdlease_count = 0, wrlease_count = 0;
@@ -1380,6 +1381,11 @@ int generic_setlease(struct file *filp, 
 		|| (atomic_read(&inode->i_count) > 1)))
 		goto out;
 
+	error = -ENOMEM;
+	new_fl = locks_alloc_lock();
+	if (new_fl == NULL)
+		goto out;
+
 	/*
 	 * At this point, we know that if there is an exclusive
 	 * lease on this file, then we hold it on this filp
@@ -1422,18 +1428,15 @@ int generic_setlease(struct file *filp, 
 	if (!leases_enable)
 		goto out;
 
-	error = -ENOMEM;
-	fl = locks_alloc_lock();
-	if (fl == NULL)
-		goto out;
-
-	locks_copy_lock(fl, lease);
-
-	locks_insert_lock(before, fl);
+	locks_copy_lock(new_fl, lease);
+	locks_insert_lock(before, new_fl);
 
 	*flp = fl;
-	error = 0;
+	return 0;
+
 out:
+	if (new_fl != NULL)
+		locks_free_lock(new_fl);
 	return error;
 }
 EXPORT_SYMBOL(generic_setlease);
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/