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    SubjectRe: [PATCH v2 07/20] randstruct: Whitelist big_key path struct overloading
    On Sun, May 28, 2017 at 9:59 AM, Kees Cook <keescook@chromium.org> wrote:
    > On Sun, May 28, 2017 at 1:12 AM, Christoph Hellwig <hch@infradead.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@lst.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@lst.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@chromium.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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