This is a note to let you know that I've just added the patch titled
staging: android: ashmem: Fix lockdep issue during llseek
to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: staging-android-ashmem-fix-lockdep-issue-during-llseek.patch and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
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 @@ -330,24 +330,23 @@ 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; }
Patches currently in stable-queue which might be from joelaf@google.com are
queue-4.4/staging-android-ashmem-fix-lockdep-issue-during-llseek.patch