On Fri, Feb 10, 2023 at 3:58 PM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
> Currently proc_dobool expects a (bool *) in table->data, but sizeof(int)
> in table->maxsize, because it uses do_proc_dointvec() directly.
>
> This is unsafe for at least two reasons:
> 1. A sysctl table definition may use { .data = &variable, .maxsize =
> sizeof(variable) }, not realizing that this makes the sysctl unusable
> (see the Fixes: tag) and that they need to use the completely
> counterintuitive sizeof(int) instead.
> 2. proc_dobool() will currently try to parse an array of values if given
> .maxsize >= 2*sizeof(int), but will try to write values of type bool
> by offsets of sizeof(int), so it will not work correctly with neither
> an (int *) nor a (bool *). There is no .maxsize validation to prevent
> this.
>
> Fix this by:
> 1. Constraining proc_dobool() to allow only one value and .maxsize ==
> sizeof(bool).
> 2. Wrapping the original struct ctl_table in a temporary one with .data
> pointing to a local int variable and .maxsize set to sizeof(int) and
> passing this one to proc_dointvec(), converting the value to/from
> bool as needed (using proc_dou8vec_minmax() as an example).
> 3. Extending sysctl_check_table() to enforce proc_dobool() expectations.
> 4. Fixing the proc_dobool() docstring (it was just copy-pasted from
> proc_douintvec, apparently...).
> 5. Converting all existing proc_dobool() users to set .maxsize to
> sizeof(bool) instead of sizeof(int).
>
> Fixes: 83efeeeb3d04 ("tty: Allow TIOCSTI to be disabled")
> Fixes: a2071573d634 ("sysctl: introduce new proc handler proc_dobool")
> Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
> ---
> fs/lockd/svc.c | 2 +-
> fs/proc/proc_sysctl.c | 6 ++++++
> kernel/sysctl.c | 43 ++++++++++++++++++++++++-------------------
> mm/hugetlb_vmemmap.c | 2 +-
> 4 files changed, 32 insertions(+), 21 deletions(-)
Gentle ping... Without this patch the new "dev.tty.legacy_tiocsti"
sysctl is unusable. This is blocking me from making selinux-testsuite
work with CONFIG_LEGACY_TIOCSTI=n:
https://lore.kernel.org/selinux/CAHC9VhQwrjwdW27+ktcT_9q-N7AmuUK8GYgoYbPXGVAcjwA4nQ@xxxxxxxxxxxxxx/T/
--
Ondrej Mosnacek
Senior Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.
