#syz test: https://github.com/joelagnel/linux.git test-ashmem
--->8----
>From 55dd7e77e0e46af101ef2195d618d5f56af1023d Mon Sep 17 00:00:00 2001
From: Joel Fernandes <joe...@google.com>
Date: Tue, 23 Jan 2018 17:45:04 -0800
Subject: [PATCH] ashmem: Fix lockdep issue during llseek
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
during a syzcaller test, this patch fixes the issue by releasing the
ashmem_mutex before the call the vfs_llseek, and reacquiring it after.
Reported-by: syzbot+8ec30bb7bf1a981a2...@syzkaller.appspotmail.com
Signed-off-by: Joel Fernandes <joe...@google.com>
---
drivers/staging/android/ashmem.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 0f695df14c9d..248983cf2db1 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -343,7 +343,9 @@ static loff_t ashmem_llseek(struct file *file, loff_t
offset, int origin)
goto out;
}
+ mutex_unlock(&ashmem_mutex);
ret = vfs_llseek(asma->file, offset, origin);
+ mutex_lock(&ashmem_mutex);
if (ret < 0)
goto out;
--
2.16.0.rc1.238.g530d649a79-goog
