linux-kernel - Re: Remove easily user-triggerable BUG from generic

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Date:	Mon, 23 Jul 2012 11:20:39 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"J. Bruce Fields" <bfields@...hat.com>
Subject: Re: Remove easily user-triggerable BUG from generic_setlease

On Fri, Jul 13, 2012 at 10:47:43AM -0700, Linus Torvalds wrote:
> On Fri, Jul 13, 2012 at 10:35 AM, Dave Jones <davej@...hat.com> wrote:
> > This can be trivially triggered from userspace by passing in something unexpected.
> 
> Argh. It looks like it would be harmless (apart from the noise),
> except we hold file_lock_lock. Which turns the BUG_ON() into not just
> "noise and kill the process", but "noise and kill the process and
> leave a nasty lock held".
> 
> This seems to go back to 3.2, so stable should be cc'd, no?

Thanks!  Yes, this fixes the bug for >=3.2, but before the addition of
this BUG() we could get memory corruption in this case.  And that
problem existed since the original introduction of the lease code, as
far as I can tell.

So we need something like the following, backported to 2.6.anything.

--b.

commit 76fca57d7f4e408fc758a42f798c2ebef54be60f
Author: J. Bruce Fields <bfields@...hat.com>
Date:   Wed Jul 18 17:45:42 2012 -0600

    locks: fix checking of fcntl_setlease argument
    
    The only checks of the long argument passed to fcntl(fd,F_SETLEASE,.)
    are done after converting the long to an int.  Thus some illegal values
    may be let through and cause problems in later code.
    
    Cc: stable@...r.kernel.org
    Signed-off-by: J. Bruce Fields <bfields@...hat.com>

diff --git a/fs/locks.c b/fs/locks.c
index 43797a9..ad1de47 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -311,7 +311,7 @@ static int flock_make_lock(struct file *filp, struct file_lock **lock,
 	return 0;
 }
 
-static int assign_type(struct file_lock *fl, int type)
+static int assign_type(struct file_lock *fl, long type)
 {
 	switch (type) {
 	case F_RDLCK:
@@ -448,7 +448,7 @@ static const struct lock_manager_operations lease_manager_ops = {
 /*
  * Initialize a lease, use the default lock manager operations
  */
-static int lease_init(struct file *filp, int type, struct file_lock *fl)
+static int lease_init(struct file *filp, long type, struct file_lock *fl)
  {
 	if (assign_type(fl, type) != 0)
 		return -EINVAL;
@@ -466,7 +466,7 @@ static int lease_init(struct file *filp, int type, struct file_lock *fl)
 }
 
 /* Allocate a file_lock initialised to this type of lease */
-static struct file_lock *lease_alloc(struct file *filp, int type)
+static struct file_lock *lease_alloc(struct file *filp, long type)
 {
 	struct file_lock *fl = locks_alloc_lock();
 	int error = -ENOMEM;
--
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