linux-kernel - [PATCH] btrfs: Don't pass NULL ptr to func that may deref it.

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Message-ID: <alpine.LNX.2.00.1012252214540.10759@swampdragon.chaosbits.net>
Date:	Sat, 25 Dec 2010 22:22:30 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	linux-btrfs@...r.kernel.org
cc:	linux-kernel@...r.kernel.org, Chris Mason <chris.mason@...cle.com>
Subject: [PATCH] btrfs: Don't pass NULL ptr to func that may deref it.

Hi,

In fs/btrfs/inode.c::fixup_tree_root_location() we have this code:

...
 		if (!path) {
 			err = -ENOMEM;
 			goto out;
 		}
...
 	out:
 		btrfs_free_path(path);
 		return err;

btrfs_free_path() passes its argument on to other functions and some of 
them end up dereferencing the pointer.
In the code above that pointer is clearly NULL, so btrfs_free_path() will 
eventually cause a NULL dereference.

There are many ways to cut this cake (fix the bug). The one I chose was to 
make btrfs_free_path() deal gracefully with NULL pointers. If you 
disagree, feel free to come up with an alternative patch.

Signed-off-by: Jesper Juhl <jj@...osbits.net>
---
 ctree.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 9ac1715..99599f1 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -105,6 +105,8 @@ noinline void btrfs_clear_path_blocking(struct btrfs_path *p,
 /* this also releases the path */
 void btrfs_free_path(struct btrfs_path *p)
 {
+	if (!p)
+		return;
 	btrfs_release_path(NULL, p);
 	kmem_cache_free(btrfs_path_cachep, p);
 }

-- 
Jesper Juhl <jj@...osbits.net>            http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.

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