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Date: Mon, 19 Jun 2017 12:24:13 -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 9:59 AM, Kees Cook <keescook@...omium.org> wrote:
> 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>
David, if you can Ack this, I'll carry it in my tree.
Thanks!
-Kees
>
> -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
--
Kees Cook
Pixel Security
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