On 30.04.2019 11:18, Michal Koutný wrote:
> Since commit 88aa7cc688d4 ("mm: introduce arg_lock to protect
> arg_start|end and env_start|end in mm_struct") we use arg_lock for
> boundaries modifications. Synchronize prctl_set_mm with this lock and
> keep mmap_sem for reading only (analogous to what we already do in
> prctl_set_mm_map).
>
> v2: call find_vma without arg_lock held
>
> CC: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
> CC: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
> Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx>
> ---
> kernel/sys.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sys.c b/kernel/sys.c
> index e1acb444d7b0..641fda756575 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2123,9 +2123,14 @@ static int prctl_set_mm(int opt, unsigned long addr,
>
> error = -EINVAL;
>
> - down_write(&mm->mmap_sem);
> + /*
> + * arg_lock protects concurent updates of arg boundaries, we need mmap_sem for
> + * a) concurrent sys_brk, b) finding VMA for addr validation.
> + */
> + down_read(&mm->mmap_sem);
> vma = find_vma(mm, addr);
>
> + spin_lock(&mm->arg_lock);
> prctl_map.start_code = mm->start_code;
> prctl_map.end_code = mm->end_code;
> prctl_map.start_data = mm->start_data;
> @@ -2213,7 +2218,8 @@ static int prctl_set_mm(int opt, unsigned long addr,
>
> error = 0;
> out:
> - up_write(&mm->mmap_sem);
> + spin_unlock(&mm->arg_lock);
> + up_read(&mm->mmap_sem);
> return error;
Hm, shouldn't spin_lock()/spin_unlock() pair go as a fixup to existing code
in a separate patch?
Without them, the existing code has a problem at least in get_mm_cmdline().
