On Wed, Dec 29, 2021 at 10:16:22AM +0100, Christophe JAILLET wrote:

Le 28/12/2021 à 23:49, Alan Stern a écrit :

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On Tue, Dec 28, 2021 at 08:47:15AM +0100, Christophe JAILLET wrote:

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Hi,

(2nd try - text only format - sorry for the noise)


first try to use syzbot. I hope I do it right.
Discussion about the syz report can be found at
https://lore.kernel.org/linux-kernel/0000000000007d25ff059457342d@google.com/ (local)

This patch only test if alauda_get_media_status() (and its embedded
usb_stor_ctrl_transfer()) before using the data.
In case of error, it returns USB_STOR_TRANSPORT_ERROR as done elsewhere.

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
master

CJ

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diff --git a/drivers/usb/storage/alauda.c b/drivers/usb/storage/alauda.c
index 20b857e97e60..6c486d964911 100644
--- a/drivers/usb/storage/alauda.c
+++ b/drivers/usb/storage/alauda.c

@@ -318,7 +318,8 @@ static int alauda_get_media_status(struct us_data *us, unsigned char *data)
  	rc = usb_stor_ctrl_transfer(us, us->recv_ctrl_pipe,
  		command, 0xc0, 0, 1, data, 2);
-	usb_stor_dbg(us, "Media status %02X %02X\n", data[0], data[1]);
+	if (rc == USB_STOR_XFER_GOOD)
+		usb_stor_dbg(us, "Media status %02X %02X\n", data[0], data[1]);

Instead of adding this test, you could initialize data[0] and data[1]
to zero before the call to usb_stor_ctrl_transfer.

Well, having the test is cleaner, IMHO.
If usb_stor_ctrl_transfer() fails, a message explaining the reason is
already generated by the same usb_stor_dbg(). Having an error message
followed by another one stating that the Media Status is 0x00 0x00 could be
confusing I think.

Let me know if you have a real preference for a memset(data, 0, 2).
If so, I'll add it.

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  	return rc;
  }

@@ -453,8 +454,11 @@ static int alauda_check_media(struct us_data *us)
  {
  	struct alauda_info *info = (struct alauda_info *) us->extra;
  	unsigned char status[2];
+	int rc;
-	alauda_get_media_status(us, status);
+	rc = alauda_get_media_status(us, status);
+	if (rc != USB_STOR_TRANSPORT_GOOD)
+		return USB_STOR_TRANSPORT_ERROR;
  	/* Check for no media or door open */
  	if ((status[0] & 0x80) || ((status[0] & 0x1F) == 0x10)

In general this looks fine.  Let us know when you are ready to submit
the patch.

I was unsure that this patch would get any interest because the driver looks
old. That's why I first tried to play with syzbot :)

It is indeed old.  I doubt very many devices of this type are still in 
use.

In the syzbot history, you also mentioned that 'unsigned char status[2]'
should be 'unsigned char *status = us->iobuf;'

This is more a blind fix for me, but it looks consistent with other places
that call alauda_get_media_status().

So, once you confirm if you prefer my 'if' or a 'memset', I'll resend a
small serie for fixing both issues.

"if" and "memset" are both acceptable.  You can use either one.

Alan Stern