linux-kernel - Re: KASAN: use-after-free Read in sg

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Message-ID: <404508f8-37bb-a3bd-4319-6b6d7a7e076e@cybernetics.com>
Date:   Thu, 22 Sep 2022 11:29:02 -0400
From:   Tony Battersby <tonyb@...ernetics.com>
To:     Rondreis <linhaoguo86@...il.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Douglas Gilbert <dgilbert@...erlog.com>
Subject: Re: KASAN: use-after-free Read in sg_release

On 9/20/22 10:46, Rondreis wrote:
> Hello,
>
> When fuzzing the Linux kernel driver v6.0-rc6, the following crash was
> triggered.
>
> HEAD commit: 521a547ced6477c54b4b0cc206000406c221b4d6
> git tree: upstream
>
> kernel config: https://pastebin.com/raw/hekxU61F
> console output: https://pastebin.com/raw/73a8RzBY
>
> Sorry for failing to extract the reproducer. But on other versions of
> Linux, I also triggered this crash.
>
> I would appreciate it if you have any idea how to solve this bug.
>
sg_release() calls "kref_put(&sfp->f_ref, sg_remove_sfp)" which
eventually does "kref_put(&sdp->d_ref, sg_device_destroy)" which does
"kfree(sdp)", but sg_release() continues to access sdp afterward.  Try
the following patch.

>From 82ca6785c40eded6229183a53752fc5e43db4a94 Mon Sep 17 00:00:00 2001
From: Tony Battersby <tonyb@...ernetics.com>
Date: Thu, 22 Sep 2022 11:05:30 -0400
Subject: [PATCH] scsi: sg: fix memory-use-after-free on device removal

Fix memory-use-after-free race when closing a sg fd to a removed device.

Link: https://lore.kernel.org/linux-scsi/CAB7eexK_jr1LWOO9RWrBF9as7gAS9kpHjrZFRuRrRJF=1H4W6A@mail.gmail.com/
Reported-by: Rondreis <linhaoguo86@...il.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Tony Battersby <tonyb@...ernetics.com>
---
 drivers/scsi/sg.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 340b050ad28d..f44cbe42dba9 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -388,6 +388,7 @@ sg_release(struct inode *inode, struct file *filp)
 		return -ENXIO;
 	SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sdp, "sg_release\n"));
 
+	kref_get(&sdp->d_ref);
 	mutex_lock(&sdp->open_rel_lock);
 	scsi_autopm_put_device(sdp->device);
 	kref_put(&sfp->f_ref, sg_remove_sfp);
@@ -402,6 +403,7 @@ sg_release(struct inode *inode, struct file *filp)
 		wake_up_interruptible(&sdp->open_wait);
 	}
 	mutex_unlock(&sdp->open_rel_lock);
+	kref_put(&sdp->d_ref, sg_device_destroy);
 	return 0;
 }
 
-- 
2.25.1