staging: android: ashmem: Fix possible deadlock in ashmem_ioctl
authorYisheng Xie <xieyisheng1@huawei.com>
Wed, 28 Feb 2018 06:59:22 +0000 (14:59 +0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sat, 24 Mar 2018 10:01:21 +0000 (11:01 +0100)
commit23081c335df988f3ddcceae253aa7504c78c3094
tree54ed1ae35fabd8ae6bff99430895b5cddcdefce8
parent23e73e2ab4d29b481eda0026ea3266b2360b1480
staging: android: ashmem: Fix possible deadlock in ashmem_ioctl

commit 740a5759bf222332fbb5eda42f89aa25ba38f9b2 upstream.

ashmem_mutex may create a chain of dependencies like:

CPU0                                    CPU1
 mmap syscall                           ioctl syscall
 -> mmap_sem (acquired)                 -> ashmem_ioctl
 -> ashmem_mmap                            -> ashmem_mutex (acquired)
    -> ashmem_mutex (try to acquire)       -> copy_from_user
                                              -> mmap_sem (try to acquire)

There is a lock odering problem between mmap_sem and ashmem_mutex causing
a lockdep splat[1] during a syzcaller test. This patch fixes the problem
by move copy_from_user out of ashmem_mutex.

[1] https://www.spinics.net/lists/kernel/msg2733200.html

Fixes: ce8a3a9e76d0 (staging: android: ashmem: Fix a race condition in pin ioctls)
Reported-by: syzbot+d7a918a7a8e1c952bc36@syzkaller.appspotmail.com
Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
Cc: "Joel Fernandes (Google)" <joel.opensrc@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/staging/android/ashmem.c