On Wed, Jul 15, 2020 at 08:08:47PM -0700, Kees Cook wrote:
From: Romain Perier romain.perier@gmail.com
Nowadays, modern kernel subsystems that use callbacks pass the data structure associated with a given callback as argument to the callback. The tasklet subsystem remains one which passes an arbitrary unsigned long to the callback function. This has several problems:
This keeps an extra field for storing the argument in each tasklet data structure, it bloats the tasklet_struct structure with a redundant .data field
No type checking can be performed on this argument. Instead of using container_of() like other callback subsystems, it forces callbacks to do explicit type cast of the unsigned long argument into the required object type.
Buffer overflows can overwrite the .func and the .data field, so an attacker can easily overwrite the function and its first argument to whatever it wants.
Add a new tasklet initialization API, via DECLARE_TASKLET() and tasklet_setup(), which will replace the existing ones.
This work is greatly inspired by the timer_struct conversion series, see commit e99e88a9d2b0 ("treewide: setup_timer() -> timer_setup()")
To avoid problems with both -Wcast-function-type (which is enabled in the kernel via -Wextra is several subsystems), and with mismatched function prototypes when build with Control Flow Integrity enabled, this adds the "use_callback" member to let the tasklet caller choose which union member to call through. Once all old API uses are removed, this and the .data member will be removed as well. (On 64-bit this does not grow the struct size as the new member fills the hole after atomic_t, which is also "int" sized.)
Signed-off-by: Romain Perier romain.perier@gmail.com Co-developed-by: Allen Pais allen.lkml@gmail.com Signed-off-by: Allen Pais allen.lkml@gmail.com Co-developed-by: Kees Cook keescook@chromium.org Signed-off-by: Kees Cook keescook@chromium.org
include/linux/interrupt.h | 24 +++++++++++++++++++++++- kernel/softirq.c | 18 +++++++++++++++++- 2 files changed, 40 insertions(+), 2 deletions(-)
Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org