[PATCH] locks: fix checking of fcntl_setlease argument

From: J. Bruce Fields
Date: Mon Jul 23 2012 - 15:17:12 EST

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@xxxxxxxxxxxxxxx
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
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;

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