From: Oleg Nesterov oleg@redhat.com
commit 46d0b24c5ee10a15dfb25e20642f5a5ed59c5003 upstream.
userfaultfd_release() should clear vm_flags/vm_userfaultfd_ctx even if mm->core_state != NULL.
Otherwise a page fault can see userfaultfd_missing() == T and use an already freed userfaultfd_ctx.
Link: http://lkml.kernel.org/r/20190820160237.GB4983@redhat.com Fixes: 04f5866e41fb ("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping") Signed-off-by: Oleg Nesterov oleg@redhat.com Reported-by: Kefeng Wang wangkefeng.wang@huawei.com Reviewed-by: Andrea Arcangeli aarcange@redhat.com Tested-by: Kefeng Wang wangkefeng.wang@huawei.com Cc: Peter Xu peterx@redhat.com Cc: Mike Rapoport rppt@linux.ibm.com Cc: Jann Horn jannh@google.com Cc: Jason Gunthorpe jgg@mellanox.com Cc: Michal Hocko mhocko@suse.com Cc: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/userfaultfd.c | 25 +++++++++++++------------ 1 file changed, 13 insertions(+), 12 deletions(-)
--- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -464,6 +464,7 @@ static int userfaultfd_release(struct in /* len == 0 means wake all */ struct userfaultfd_wake_range range = { .len = 0, }; unsigned long new_flags; + bool still_valid;
ACCESS_ONCE(ctx->released) = true;
@@ -479,8 +480,7 @@ static int userfaultfd_release(struct in * taking the mmap_sem for writing. */ down_write(&mm->mmap_sem); - if (!mmget_still_valid(mm)) - goto skip_mm; + still_valid = mmget_still_valid(mm); prev = NULL; for (vma = mm->mmap; vma; vma = vma->vm_next) { cond_resched(); @@ -491,19 +491,20 @@ static int userfaultfd_release(struct in continue; } new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); - prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, - new_flags, vma->anon_vma, - vma->vm_file, vma->vm_pgoff, - vma_policy(vma), - NULL_VM_UFFD_CTX); - if (prev) - vma = prev; - else - prev = vma; + if (still_valid) { + prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, + new_flags, vma->anon_vma, + vma->vm_file, vma->vm_pgoff, + vma_policy(vma), + NULL_VM_UFFD_CTX); + if (prev) + vma = prev; + else + prev = vma; + } vma->vm_flags = new_flags; vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; } -skip_mm: up_write(&mm->mmap_sem); mmput(mm); wakeup: