Re: [PATCH] fsi:fsi-sbefifo: Fix possible concurrency use-after-free bugs in sbefifo_user_release

From: Jia-Ju Bai
Date: Thu Jan 03 2019 - 21:26:42 EST

On 2019/1/4 8:47, Benjamin Herrenschmidt wrote:
On Wed, 2018-12-26 at 21:56 +0800, Jia-Ju Bai wrote:
In drivers/fsi/fsi-sbefifo.c, the functions sbefifo_user_release(),
sbefifo_user_read() and sbefifo_user_write() may be concurrently executed.
So after refreshing my mind, looking at the code and talking with Al, I
really dont' see what race you are trying to fix here.

read/write should never be concurrent with release for a given file and
the stuff we are protecting here is local to the file instance.

Do you have an actual problem you observed ?

Thanks for the reply.

In fact, this report is found by a static tool written by myself, instead of real execution.
My tool found that in some drivers, for the structure "struct file_operations", the code in intetrfaces ".read" , "write" and ".release" are protected by the same lock.
The functions kcs_bmc_read(), kcs_bmc_write() and kcs_bmc_release() are examples.
Thus, my tool inferred that the intetrfaces ".read" , "write" and ".release" of "struct file_operations" can be concurrently executed, and generated this report.
I manually checked this report, but I was not very sure of it, so I marked it as a "possible bug" and reported it.

From your message, now I know my report is false, and ".read" , "write" cannot be concurrently executed with ".release" for a given file.
Sorry for my false report, and thanks for your message.

Best wishes,
Jia-Ju Bai