Btrfs: Make free_ipath() deal gracefully with NULL pointers

jjuhl · kdave · commit 4735fb282830 · 2012-04-18T19:22:20.000+02:00
Make free_ipath() behave like most other freeing functions in the
kernel and gracefully do nothing when passed a NULL pointer.

Besides this making the bahaviour consistent with functions such as
kfree(), vfree(), btrfs_free_path() etc etc, it also fixes a real NULL
deref issue in fs/btrfs/ioctl.c::btrfs_ioctl_ino_to_path(). In that
function we have this code:

...
        ipath = init_ipath(size, root, path);
        if (IS_ERR(ipath)) {
                ret = PTR_ERR(ipath);
                ipath = NULL;
                goto out;
        }
...
out:
        btrfs_free_path(path);
        free_ipath(ipath);
...

If we ever take the true branch of that 'if' statement we'll end up
passing a NULL pointer to free_ipath() which will subsequently
dereference it and we'll go "Boom" :-(
This patch will avoid that.

Signed-off-by: Jesper Juhl &lt;jj@chaosbits.net&gt;
diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
@@ -1414,6 +1414,8 @@ struct inode_fs_paths *init_ipath(s32 total_bytes, struct btrfs_root *fs_root,
 
 void free_ipath(struct inode_fs_paths *ipath)
 {
+	if (!ipath)
+		return;
 	kfree(ipath->fspath);
 	kfree(ipath);
 }

Original file line number	Diff line number	Diff line change
`@@ -1414,6 +1414,8 @@ struct inode_fs_paths init_ipath(s32 total_bytes, struct btrfs_root fs_root,`
`1414`	`1414`
`1415`	`1415`	`void free_ipath(struct inode_fs_paths *ipath)`
`1416`	`1416`	`{`
	`1417`	`+ if (!ipath)`
	`1418`	`+ return;`
`1417`	`1419`	`kfree(ipath->fspath);`
`1418`	`1420`	`kfree(ipath);`
`1419`	`1421`	`}`