This is a note to let you know that I've just added the patch titled shmem: pin the file in shmem_fault() if mmap_sem is dropped to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: shmem-pin-the-file-in-shmem_fault-if-mmap_sem-is-dropped.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 8897c1b1a1795cab23d5ac13e4e23bf0b5f4e0c6 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Date: Sat, 30 Nov 2019 17:50:26 -0800 Subject: shmem: pin the file in shmem_fault() if mmap_sem is dropped From: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> commit 8897c1b1a1795cab23d5ac13e4e23bf0b5f4e0c6 upstream. syzbot found the following crash: BUG: KASAN: use-after-free in perf_trace_lock_acquire+0x401/0x530 include/trace/events/lock.h:13 Read of size 8 at addr ffff8880a5cf2c50 by task syz-executor.0/26173 CPU: 0 PID: 26173 Comm: syz-executor.0 Not tainted 5.3.0-rc6 #146 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: perf_trace_lock_acquire+0x401/0x530 include/trace/events/lock.h:13 trace_lock_acquire include/trace/events/lock.h:13 [inline] lock_acquire+0x2de/0x410 kernel/locking/lockdep.c:4411 __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline] _raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151 spin_lock include/linux/spinlock.h:338 [inline] shmem_fault+0x5ec/0x7b0 mm/shmem.c:2034 __do_fault+0x111/0x540 mm/memory.c:3083 do_shared_fault mm/memory.c:3535 [inline] do_fault mm/memory.c:3613 [inline] handle_pte_fault mm/memory.c:3840 [inline] __handle_mm_fault+0x2adf/0x3f20 mm/memory.c:3964 handle_mm_fault+0x1b5/0x6b0 mm/memory.c:4001 do_user_addr_fault arch/x86/mm/fault.c:1441 [inline] __do_page_fault+0x536/0xdd0 arch/x86/mm/fault.c:1506 do_page_fault+0x38/0x590 arch/x86/mm/fault.c:1530 page_fault+0x39/0x40 arch/x86/entry/entry_64.S:1202 It happens if the VMA got unmapped under us while we dropped mmap_sem and inode got freed. Pinning the file if we drop mmap_sem fixes the issue. Link: http://lkml.kernel.org/r/20190927083908.rhifa4mmaxefc24r@box Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reported-by: syzbot+03ee87124ee05af991bd@xxxxxxxxxxxxxxxxxxxxxxxxx Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Hillf Danton <hdanton@xxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Josef Bacik <josef@xxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/shmem.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1989,16 +1989,14 @@ static vm_fault_t shmem_fault(struct vm_ shmem_falloc->waitq && vmf->pgoff >= shmem_falloc->start && vmf->pgoff < shmem_falloc->next) { + struct file *fpin; wait_queue_head_t *shmem_falloc_waitq; DEFINE_WAIT_FUNC(shmem_fault_wait, synchronous_wake_function); ret = VM_FAULT_NOPAGE; - if ((vmf->flags & FAULT_FLAG_ALLOW_RETRY) && - !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) { - /* It's polite to up mmap_sem if we can */ - up_read(&vma->vm_mm->mmap_sem); + fpin = maybe_unlock_mmap_for_io(vmf, NULL); + if (fpin) ret = VM_FAULT_RETRY; - } shmem_falloc_waitq = shmem_falloc->waitq; prepare_to_wait(shmem_falloc_waitq, &shmem_fault_wait, @@ -2016,6 +2014,9 @@ static vm_fault_t shmem_fault(struct vm_ spin_lock(&inode->i_lock); finish_wait(shmem_falloc_waitq, &shmem_fault_wait); spin_unlock(&inode->i_lock); + + if (fpin) + fput(fpin); return ret; } spin_unlock(&inode->i_lock); Patches currently in stable-queue which might be from kirill.shutemov@xxxxxxxxxxxxxxx are queue-4.19/shmem-pin-the-file-in-shmem_fault-if-mmap_sem-is-dropped.patch