From b120017178894e041baa51c51a197cfa82b53b45 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Thu, 14 Jun 2018 15:26:34 -0700 Subject: [PATCH] mm: check for SIGKILL inside dup_mmap() loop [ Upstream commit 655c79bb40a0870adcd0871057d01de11625882b ] As a theoretical problem, dup_mmap() of an mm_struct with 60000+ vmas can loop while potentially allocating memory, with mm->mmap_sem held for write by current thread. This is bad if current thread was selected as an OOM victim, for current thread will continue allocations using memory reserves while OOM reaper is unable to reclaim memory. As an actually observable problem, it is not difficult to make OOM reaper unable to reclaim memory if the OOM victim is blocked at i_mmap_lock_write() in this loop. Unfortunately, since nobody can explain whether it is safe to use killable wait there, let's check for SIGKILL before trying to allocate memory. Even without an OOM event, there is no point with continuing the loop from the beginning if current thread is killed. I tested with debug printk(). This patch should be safe because we already fail if security_vm_enough_memory_mm() or kmem_cache_alloc(GFP_KERNEL) fails and exit_mmap() handles it. ***** Aborting dup_mmap() due to SIGKILL ***** ***** Aborting dup_mmap() due to SIGKILL ***** ***** Aborting dup_mmap() due to SIGKILL ***** ***** Aborting dup_mmap() due to SIGKILL ***** ***** Aborting exit_mmap() due to NULL mmap ***** [akpm@linux-foundation.org: add comment] Link: http://lkml.kernel.org/r/201804071938.CDE04681.SOFVQJFtMHOOLF@I-love.SAKURA.ne.jp Signed-off-by: Tetsuo Handa Cc: Alexander Viro Cc: Rik van Riel Cc: Michal Hocko Cc: Kirill A. Shutemov Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- kernel/fork.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index a5d21c42acfc8..5ad558e6f8fe9 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -440,6 +440,14 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, continue; } charge = 0; + /* + * Don't duplicate many vmas if we've been oom-killed (for + * example) + */ + if (fatal_signal_pending(current)) { + retval = -EINTR; + goto out; + } if (mpnt->vm_flags & VM_ACCOUNT) { unsigned long len = vma_pages(mpnt); -- 2.47.2