| From cb57469c9573f6018cd1302953dd45d6e05aba7b Mon Sep 17 00:00:00 2001 |
| From: Joel Fernandes <joelaf@google.com> |
| Date: Fri, 16 Feb 2018 11:02:01 -0800 |
| Subject: staging: android: ashmem: Fix lockdep issue during llseek |
| |
| From: Joel Fernandes <joelaf@google.com> |
| |
| commit cb57469c9573f6018cd1302953dd45d6e05aba7b upstream. |
| |
| ashmem_mutex create a chain of dependencies like so: |
| |
| (1) |
| mmap syscall -> |
| mmap_sem -> (acquired) |
| ashmem_mmap |
| ashmem_mutex (try to acquire) |
| (block) |
| |
| (2) |
| llseek syscall -> |
| ashmem_llseek -> |
| ashmem_mutex -> (acquired) |
| inode_lock -> |
| inode->i_rwsem (try to acquire) |
| (block) |
| |
| (3) |
| getdents -> |
| iterate_dir -> |
| inode_lock -> |
| inode->i_rwsem (acquired) |
| copy_to_user -> |
| mmap_sem (try to acquire) |
| |
| There is a lock ordering created between mmap_sem and inode->i_rwsem |
| causing a lockdep splat [2] during a syzcaller test, this patch fixes |
| the issue by unlocking the mutex earlier. Functionally that's Ok since |
| we don't need to protect vfs_llseek. |
| |
| [1] https://patchwork.kernel.org/patch/10185031/ |
| [2] https://lkml.org/lkml/2018/1/10/48 |
| |
| Acked-by: Todd Kjos <tkjos@google.com> |
| Cc: Arve Hjonnevag <arve@android.com> |
| Cc: stable@vger.kernel.org |
| Reported-by: syzbot+8ec30bb7bf1a981a2012@syzkaller.appspotmail.com |
| Signed-off-by: Joel Fernandes <joelaf@google.com> |
| Acked-by: Greg Hackmann <ghackmann@google.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| drivers/staging/android/ashmem.c | 15 +++++++-------- |
| 1 file changed, 7 insertions(+), 8 deletions(-) |
| |
| --- a/drivers/staging/android/ashmem.c |
| +++ b/drivers/staging/android/ashmem.c |
| @@ -334,24 +334,23 @@ static loff_t ashmem_llseek(struct file |
| mutex_lock(&ashmem_mutex); |
| |
| if (asma->size == 0) { |
| - ret = -EINVAL; |
| - goto out; |
| + mutex_unlock(&ashmem_mutex); |
| + return -EINVAL; |
| } |
| |
| if (!asma->file) { |
| - ret = -EBADF; |
| - goto out; |
| + mutex_unlock(&ashmem_mutex); |
| + return -EBADF; |
| } |
| |
| + mutex_unlock(&ashmem_mutex); |
| + |
| ret = vfs_llseek(asma->file, offset, origin); |
| if (ret < 0) |
| - goto out; |
| + return ret; |
| |
| /** Copy f_pos from backing file, since f_ops->llseek() sets it */ |
| file->f_pos = asma->file->f_pos; |
| - |
| -out: |
| - mutex_unlock(&ashmem_mutex); |
| return ret; |
| } |
| |