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Date: Sun, 28 May 2017 09:59:31 -0700
From: Kees Cook <keescook@...omium.org>
To: Christoph Hellwig <hch@...radead.org>, David Howells <dhowells@...hat.com>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Laura Abbott <labbott@...hat.com>,
"x86@...nel.org" <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 07/20] randstruct: Whitelist big_key path struct overloading
On Sun, May 28, 2017 at 1:12 AM, Christoph Hellwig <hch@...radead.org> wrote:
> What about the untested patch below to just fix the issue?
>
> ---
> From e9eb519c854d2f3d16a4def492577a883246e290 Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@....de>
> Date: Sun, 28 May 2017 11:03:34 +0300
> Subject: security/keys: don't cast union key_payload
>
> Instead store the individual pointers in struct path.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
Yeah, this is less invasive than what I'd proposed to David to fix it
earlier. David, does this look okay to you?
Reviewed-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> security/keys/big_key.c | 35 ++++++++++++++++++++---------------
> 1 file changed, 20 insertions(+), 15 deletions(-)
>
> diff --git a/security/keys/big_key.c b/security/keys/big_key.c
> index 835c1ab30d01..06f2cd07dbd7 100644
> --- a/security/keys/big_key.c
> +++ b/security/keys/big_key.c
> @@ -26,8 +26,8 @@
> */
> enum {
> big_key_data,
> - big_key_path,
> - big_key_path_2nd_part,
> + big_key_path_mnt,
> + big_key_path_dentry,
> big_key_len,
> };
>
> @@ -118,12 +118,16 @@ static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
> return ret;
> }
>
> +#define PATH_FROM_PAYLOAD(p) { \
> + .mnt = (p)->data[big_key_path_mnt], \
> + .dentry = (p)->data[big_key_path_dentry], \
> +}
> +
> /*
> * Preparse a big key
> */
> int big_key_preparse(struct key_preparsed_payload *prep)
> {
> - struct path *path = (struct path *)&prep->payload.data[big_key_path];
> struct file *file;
> u8 *enckey;
> u8 *data = NULL;
> @@ -190,9 +194,10 @@ int big_key_preparse(struct key_preparsed_payload *prep)
> /* Pin the mount and dentry to the key so that we can open it again
> * later
> */
> + path_get(&file->f_path);
> prep->payload.data[big_key_data] = enckey;
> - *path = file->f_path;
> - path_get(path);
> + prep->payload.data[big_key_path_mnt] = file->f_path.mnt;
> + prep->payload.data[big_key_path_dentry] = file->f_path.dentry;
> fput(file);
> kfree(data);
> } else {
> @@ -222,9 +227,9 @@ int big_key_preparse(struct key_preparsed_payload *prep)
> void big_key_free_preparse(struct key_preparsed_payload *prep)
> {
> if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
> - struct path *path = (struct path *)&prep->payload.data[big_key_path];
> + struct path path = PATH_FROM_PAYLOAD(&prep->payload);
>
> - path_put(path);
> + path_put(&path);
> }
> kfree(prep->payload.data[big_key_data]);
> }
> @@ -235,13 +240,13 @@ void big_key_free_preparse(struct key_preparsed_payload *prep)
> */
> void big_key_revoke(struct key *key)
> {
> - struct path *path = (struct path *)&key->payload.data[big_key_path];
> + struct path path = PATH_FROM_PAYLOAD(&key->payload);
>
> /* clear the quota */
> key_payload_reserve(key, 0);
> if (key_is_instantiated(key) &&
> (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
> - vfs_truncate(path, 0);
> + vfs_truncate(&path, 0);
> }
>
> /*
> @@ -252,11 +257,11 @@ void big_key_destroy(struct key *key)
> size_t datalen = (size_t)key->payload.data[big_key_len];
>
> if (datalen > BIG_KEY_FILE_THRESHOLD) {
> - struct path *path = (struct path *)&key->payload.data[big_key_path];
> + struct path path = PATH_FROM_PAYLOAD(&key->payload);
>
> - path_put(path);
> - path->mnt = NULL;
> - path->dentry = NULL;
> + path_put(&path);
> + key->payload.data[big_key_path_mnt] = NULL;
> + key->payload.data[big_key_path_dentry] = NULL;
> }
> kfree(key->payload.data[big_key_data]);
> key->payload.data[big_key_data] = NULL;
> @@ -290,7 +295,7 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
> return datalen;
>
> if (datalen > BIG_KEY_FILE_THRESHOLD) {
> - struct path *path = (struct path *)&key->payload.data[big_key_path];
> + struct path path = PATH_FROM_PAYLOAD(&key->payload);
> struct file *file;
> u8 *data;
> u8 *enckey = (u8 *)key->payload.data[big_key_data];
> @@ -300,7 +305,7 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
> if (!data)
> return -ENOMEM;
>
> - file = dentry_open(path, O_RDONLY, current_cred());
> + file = dentry_open(&path, O_RDONLY, current_cred());
> if (IS_ERR(file)) {
> ret = PTR_ERR(file);
> goto error;
> --
> 2.11.0
>
--
Kees Cook
Pixel Security
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