linux-kernel - [PATCH] locks: fix checking of fcntl

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Date:	Mon, 23 Jul 2012 15:17:17 -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: [PATCH] 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.

(They actually *don't* cause problems in mainline, as of Dave Jones's
8d657eb3b43861064d36241e88d9d61c709f33f0 "Remove easily user-triggerable
BUG from generic_setlease", but we should fix this anyway.  And this
patch will be necessary to fix real bugs on earlier kernels.)

Cc: stable@...r.kernel.org
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
---
 fs/locks.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

On Mon, Jul 23, 2012 at 12:09:21PM -0700, Linus Torvalds wrote:
> NEVER EVER add BUG() as a "well, that was unexpected". That way lies
> exactly the kinds of denial-of-service attacks that that BUG() caused.

OK, makes sense.  Resending the patch to make it clear it's intended for
mainline as well.--b.

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;
-- 
1.7.9.5

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