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 <[email protected]> CC: Laurent Dufour <[email protected]> Signed-off-by: Michal Koutný <[email protected]> --- 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; } -- 2.16.4
