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SubjectRe: [PATCH] LoadPin: Ignore the "contents" argument of the LSM hooks
On Wed, Dec 14, 2022 at 11:51:15AM +0800, Ping-Ke Shih wrote:
> From: Kees Cook <keescook@chromium.org>
>
> > LoadPin only enforces the read-only origin of kernel file reads. Whether
> > or not it was a partial read isn't important. Remove the overly
> > conservative checks so that things like partial firmware reads will
> > succeed (i.e. reading a firmware header).
> >
> > Fixes: 2039bda1fa8d ("LSM: Add "contents" flag to kernel_read_file hook")
> > Cc: Paul Moore <paul@paul-moore.com>
> > Cc: James Morris <jmorris@namei.org>
> > Cc: "Serge E. Hallyn" <serge@hallyn.com>
> > Cc: linux-security-module@vger.kernel.org
> > Signed-off-by: Kees Cook <keescook@chromium.org>
>
> Tested-by: Ping-Ke Shih <pkshih@realtek.com>

Thanks for testing!

-Kees

>
> > ---
> > security/loadpin/loadpin.c | 30 ++++++++++++++++++------------
> > 1 file changed, 18 insertions(+), 12 deletions(-)
> >
> > diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
> > index de41621f4998..110a5ab2b46b 100644
> > --- a/security/loadpin/loadpin.c
> > +++ b/security/loadpin/loadpin.c
> > @@ -122,21 +122,11 @@ static void loadpin_sb_free_security(struct super_block *mnt_sb)
> > }
> > }
> >
> > -static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
> > - bool contents)
> > +static int loadpin_check(struct file *file, enum kernel_read_file_id id)
> > {
> > struct super_block *load_root;
> > const char *origin = kernel_read_file_id_str(id);
> >
> > - /*
> > - * If we will not know that we'll be seeing the full contents
> > - * then we cannot trust a load will be complete and unchanged
> > - * off disk. Treat all contents=false hooks as if there were
> > - * no associated file struct.
> > - */
> > - if (!contents)
> > - file = NULL;
> > -
> > /* If the file id is excluded, ignore the pinning. */
> > if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
> > ignore_read_file_id[id]) {
> > @@ -192,9 +182,25 @@ static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
> > return 0;
> > }
> >
> > +static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
> > + bool contents)
> > +{
> > + /*
> > + * LoadPin only cares about the _origin_ of a file, not its
> > + * contents, so we can ignore the "are full contents available"
> > + * argument here.
> > + */
> > + return loadpin_check(file, id);
> > +}
> > +
> > static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
> > {
> > - return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents);
> > + /*
> > + * LoadPin only cares about the _origin_ of a file, not its
> > + * contents, so a NULL file is passed, and we can ignore the
> > + * state of "contents".
> > + */
> > + return loadpin_check(NULL, (enum kernel_read_file_id) id);
> > }
> >
> > static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
> > --
> > 2.34.1
>
>

--
Kees Cook

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