#syz test: https://github.com/joelagnel/linux.git test-ashmem --->8---- >From 55dd7e77e0e46af101ef2195d618d5f56af1023d Mon Sep 17 00:00:00 2001 From: Joel Fernandes <joelaf@xxxxxxxxxx> 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+8ec30bb7bf1a981a2012@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Joel Fernandes <joelaf@xxxxxxxxxx> --- 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
