Re: [patch for-3.7] fs, xattr: fix bug when removing a name not in
xattr list
[Posted December 19, 2012 by corbet]
| From: |
| Hugh Dickins <hughd-AT-google.com> |
| To: |
| David Rientjes <rientjes-AT-google.com> |
| Subject: |
| Re: [patch for-3.7] fs, xattr: fix bug when removing a name not in
xattr list |
| Date: |
| Wed, 17 Oct 2012 20:55:49 -0700 (PDT) |
| Message-ID: |
| <alpine.LSU.2.00.1210172052420.20979@eggly.anvils> |
| Cc: |
| Linus Torvalds <torvalds-AT-linux-foundation.org>,
Al Viro <viro-AT-zeniv.linux.org.uk>,
Fengguang Wu <fengguang.wu-AT-intel.com>,
Li Zefan <lizefan-AT-huawei.com>,
Aristeu Rozanski <aris-AT-redhat.com>, Tejun Heo <tj-AT-kernel.org>,
Mimi Zohar <zohar-AT-linux.vnet.ibm.com>,
James Morris <jmorris-AT-namei.org>,
Dmitry Kasatkin <dmitry.kasatkin-AT-intel.com>,
linux-security-module-AT-vger.kernel.org,
linux-kernel-AT-vger.kernel.org,
Konrad Rzeszutek Wilk <konrad.wilk-AT-oracle.com> |
| Archive‑link: | |
Article |
On Wed, 17 Oct 2012, David Rientjes wrote:
> Commit 38f38657444d ("xattr: extract simple_xattr code from tmpfs") moved
> some code from tmpfs but introduced a subtle bug along the way.
>
> 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>
Acked-by: Hugh Dickins <hughd@google.com>
Thank you both: a fine example of the danger of uninitialized_var()!
> ---
> 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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