diff options
| author | Joel Fernandes <joelaf@google.com> | 2018-02-16 11:02:01 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-03-18 11:17:53 +0100 |
| commit | e29c324dd91e38dd262e09d33fda93b0dbccaf90 (patch) | |
| tree | 67c276dc51d47fedeb21cd56e162d84caf62421c | |
| parent | 76e267cd2db69c2574f6df5424fec5b01fdc3e87 (diff) | |
staging: android: ashmem: Fix lockdep issue during llseek
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>
| -rw-r--r-- | drivers/staging/android/ashmem.c | 15 |
1 files changed, 7 insertions, 8 deletions
diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c index ec31b53ae3a5..f5b5bec6f3c1 100644 --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -330,24 +330,23 @@ static loff_t ashmem_llseek(struct file *file, loff_t offset, int origin) 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; } |