On Sat, Nov 16, 2013 at 11:01 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> Nobody actually needs MMF_DUMPABLE/MMF_DUMP_SECURELY, there
> are only used to enforce the encoding of SUID_DUMP_* enum in
> mm->flags & MMF_DUMPABLE_MASK.
>
> Now that set_dumpable() updates both bits atomically we can
> kill them and simply store the value "as is" in 2 lower bits.
>
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> ---
> fs/exec.c | 18 +++---------------
> include/linux/sched.h | 4 +---
> 2 files changed, 4 insertions(+), 18 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 613c9dc..5303005 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1620,8 +1620,7 @@ void set_binfmt(struct linux_binfmt *new)
> EXPORT_SYMBOL(set_binfmt);
>
> /*
> - * set_dumpable converts traditional three-value dumpable to two flags and
> - * stores them into mm->flags.
> + * set_dumpable stores three-value SUID_DUMP_* into mm->flags.
> */
> void set_dumpable(struct mm_struct *mm, int value)
> {
> @@ -1629,24 +1628,13 @@ void set_dumpable(struct mm_struct *mm, int value)
>
> do {
> old = ACCESS_ONCE(mm->flags);
> - new = old & ~MMF_DUMPABLE_MASK;
> -
> - switch (value) {
> - case SUID_DUMP_ROOT:
> - new |= (1 << MMF_DUMP_SECURELY);
> - case SUID_DUMP_USER:
> - new |= (1<< MMF_DUMPABLE);
> - }
> -
> + new = (old & ~MMF_DUMPABLE_MASK) | value;
Just to make this safe against insane callers, perhaps mask the value as well?
new = (old & ~MMF_DUMPABLE_MASK) | (value & MMF_DUMPABLE_MASK);
> } while (cmpxchg(&mm->flags, old, new) != old);
> }
>
> int __get_dumpable(unsigned long mm_flags)
> {
> - int ret;
> -
> - ret = mm_flags & MMF_DUMPABLE_MASK;
> - return (ret > SUID_DUMP_USER) ? SUID_DUMP_ROOT : ret;
> + return mm_flags & MMF_DUMPABLE_MASK;
> }
>
> /*
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 838a3d9..828c00d 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -326,10 +326,8 @@ extern int get_dumpable(struct mm_struct *mm);
> #define SUID_DUMP_ROOT 2 /* Dump as root */
>
> /* mm flags */
> -/* dumpable bits */
> -#define MMF_DUMPABLE 0 /* core dump is permitted */
> -#define MMF_DUMP_SECURELY 1 /* core file is readable only by root */
>
> +/* for SUID_DUMP_* above */
> #define MMF_DUMPABLE_BITS 2
> #define MMF_DUMPABLE_MASK ((1 << MMF_DUMPABLE_BITS) - 1)
Besides that, looks great.
-Kees
--
Kees Cook
Chrome OS Security
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