Re: [patch for-3.7] fs, xattr: fix bug when removing a name not in xattr list

Hillf Danton
2012-10-18T12:43:08Z

Hi David,

On Thu, Oct 18, 2012 at 11:41 AM, David Rientjes <rientjes@google.com> wrote:
> Commit 38f38657444d ("xattr: extract simple_xattr code from tmpfs") moved
> some code from tmpfs but introduced a subtle bug along the way.
>
That commit is fine but you did revert commit b9d6cfdeaf67(xattr: mark
variable as uninitialized to make both gcc and smatch happy), too late
to spin?

Hillf
> If the name passed to simple_xattr_remove() does not exist in the list of
> xattrs, then it is possible to call kfree(new_xattr) when new_xattr is
> actually initialized to itself on the stack via uninitialized_var().
>
> This causes a BUG() since the memory was not allocated via the slab
> allocator and was not bypassed through to the page allocator because it
> was too large.
>
> Initialize the local variable to NULL so the kfree() never takes place.
>
> Reported-by: Fengguang Wu <fengguang.wu@intel.com>
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
> fs/xattr.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -846,7 +846,7 @@ static int __simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
> const void *value, size_t size, int flags)
> {
> struct simple_xattr *xattr;
> - struct simple_xattr *uninitialized_var(new_xattr);
> + struct simple_xattr *new_xattr = NULL;
> int err = 0;
>
> /* value == NULL means remove */
> --
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