linux-kernel - [PATCH 1/1] locks: prevent side-effects of locks_release_private before file

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Message-Id: <1339815965-1171-2-git-send-email-filbranden@gmail.com>
Date:	Fri, 15 Jun 2012 23:06:05 -0400
From:	Filipe Brandenburger <filbranden@...il.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Matthew Wilcox <matthew@....cx>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Filipe Brandenburger <filbranden@...il.com>
Subject: [PATCH 1/1] locks: prevent side-effects of locks_release_private before file_lock is initialized

When calling fcntl(F_SETLEASE) for a second time on the same fd, do_fcntl_add_lease
will allocate and initialize a new file_lock, then if __vfs_setlease decides to
reuse the existing file_lock it will free the newly allocated one to prevent leaking
memory.

However, the new file_lock was initialized to the point where it has a valid file
descriptor pointer and lmops, so calling locks_free_lock will trigger a call to
lease_release_private_callback which will have the side effect of clearing the
fcntl(F_SETOWN) and fcntl(F_SETSIG) settings for the file descriptor even though
that was not supposed to happen at that point.

This patch will fix this by calling kmem_cache_free(filelock_cache, fl) instead of
locks_free_lock(fl) if the file_lock is not completely initialized and actually
associated to the file descriptor, avoiding the call to lease_release_private_callback
with the undesired side effects.

Signed-off-by: Filipe Brandenburger <filbranden@...il.com>
---
 fs/locks.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 814c51d..ce57c59 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -473,7 +473,7 @@ static struct file_lock *lease_alloc(struct file *filp, int type)

 	error = lease_init(filp, type, fl);
 	if (error) {
-		locks_free_lock(fl);
+		kmem_cache_free(filelock_cache, fl);
 		return ERR_PTR(error);
 	}
 	return fl;
@@ -1538,7 +1538,7 @@ static int do_fcntl_add_lease(unsigned int fd, struct file *filp, long arg)

 	new = fasync_alloc();
 	if (!new) {
-		locks_free_lock(fl);
+		kmem_cache_free(filelock_cache, fl);
 		return -ENOMEM;
 	}
 	ret = fl;
@@ -1546,11 +1546,11 @@ static int do_fcntl_add_lease(unsigned int fd, struct file *filp, long arg)
 	error = __vfs_setlease(filp, arg, &ret);
 	if (error) {
 		unlock_flocks();
-		locks_free_lock(fl);
+		kmem_cache_free(filelock_cache, fl);
 		goto out_free_fasync;
 	}
 	if (ret != fl)
-		locks_free_lock(fl);
+		kmem_cache_free(filelock_cache, fl);

 	/*
 	 * fasync_insert_entry() returns the old entry if any.
-- 
1.7.7.6

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