On 02/22/2018 01:02 PM, Joel Fernandes wrote: > (reposting in plain text, sorry for the previous HTML email, I should > have not posted from the Phone) > > On Thu, Feb 22, 2018 at 5:48 AM, Greg Kroah-Hartman > <[email protected]> wrote: >> On Fri, Feb 16, 2018 at 11:02:01AM -0800, Joel Fernandes wrote: >>> 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 >>> >>> Cc: Todd Kjos <[email protected]> >>> Cc: Arve Hjonnevag <[email protected]> >>> Cc: Greg Hackmann <[email protected]> >>> Cc: Greg Kroah-Hartman <[email protected]> >>> Cc: [email protected] >>> Reported-by: [email protected] >>> Signed-off-by: Joel Fernandes <[email protected]> >>> --- >>> Changes since first version: >>> Don't relock after vfs call since its not needed. Only reason we lock is >>> to protect races with asma->file. >>> https://patchwork.kernel.org/patch/10185031/ >> >> I'd like some acks from others before I take this patch. > > GregH, Todd, could you provide Acks?
Acked-by: Greg Hackmann <[email protected]>
