Re: Remove easily user-triggerable BUG from generic_setlease

From: J. Bruce Fields
Date: Mon Jul 23 2012 - 11:20:35 EST

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@xxxxxxxxxx> 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.


commit 76fca57d7f4e408fc758a42f798c2ebef54be60f
Author: J. Bruce Fields <bfields@xxxxxxxxxx>
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@xxxxxxxxxxxxxxx
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>

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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