Re: [syzbot] KMSAN: kernel-usb-infoleak in usbnet_write_cmd (3)

[Pavel Skripkin <paskripkin@gmail.com>]

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On 1/5/22 21:28, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    81c325bbf94e kmsan: hooks: do not check memory in kmsan_in..
> git tree:       https://github.com/google/kmsan.git master
> console output: https://syzkaller.appspot.com/x/log.txt?x=14a07163b00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2d8b9a11641dc9aa
> dashboard link: https://syzkaller.appspot.com/bug?extid=003c0a286b9af5412510
> compiler:       clang version 14.0.0 (/usr/local/google/src/llvm-git-monorepo 2b554920f11c8b763cd9ed9003f4e19b919b8e1f), GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=100165dbb00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10c97e77b00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+003c0a286b9af5412510@syzkaller.appspotmail.com
> 

Heh, I think, more reports like this will appear soon. Syzbot learned 
how to tweak usb read functions return values, I guess?

#syz test: https://github.com/google/kmsan.git master



With regards,
Pavel Skripkin

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diff --git a/drivers/net/usb/mcs7830.c b/drivers/net/usb/mcs7830.c
index 326cc4e749d8..0daae7f16da9 100644
--- a/drivers/net/usb/mcs7830.c
+++ b/drivers/net/usb/mcs7830.c
@@ -108,8 +108,16 @@ static const char driver_name[] = "MOSCHIP usb-ethernet driver";
 
 static int mcs7830_get_reg(struct usbnet *dev, u16 index, u16 size, void *data)
 {
-	return usbnet_read_cmd(dev, MCS7830_RD_BREQ, MCS7830_RD_BMREQ,
-				0x0000, index, data, size);
+	int ret;
+
+	ret = usbnet_read_cmd(dev, MCS7830_RD_BREQ, MCS7830_RD_BMREQ,
+			      0x0000, index, data, size);
+	if (ret < 0)
+		return ret;
+	else if (ret < size)
+		return -ENODATA;
+
+	return 0;
 }
 
 static int mcs7830_set_reg(struct usbnet *dev, u16 index, u16 size, const void *data)