linux-kernel - [PATCH v2] xen/hvc: replace BUG_ON() with negative return value

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Date:   Wed,  7 Jul 2021 11:10:45 +0200
From:   Juergen Gross <jgross@...e.com>
To:     xen-devel@...ts.xenproject.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Subject: [PATCH v2] xen/hvc: replace BUG_ON() with negative return value

Xen frontends shouldn't BUG() in case of illegal data received from
their backends. So replace the BUG_ON()s when reading illegal data from
the ring page with negative return values.

Signed-off-by: Juergen Gross <jgross@...e.com>
---
V2:
- drop BUG_ON() (Christophe Leroy, Greg Kroah-Hartmann)
- replace WARN_ONCE() by pr_err_once() (Greg Kroah-Hartmann)
- break out from original series
---
 drivers/tty/hvc/hvc_xen.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
index 92c9a476defc..8f143c09a169 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -86,7 +86,11 @@ static int __write_console(struct xencons_info *xencons,
 	cons = intf->out_cons;
 	prod = intf->out_prod;
 	mb();			/* update queue values before going on */
-	BUG_ON((prod - cons) > sizeof(intf->out));
+
+	if ((prod - cons) > sizeof(intf->out)) {
+		pr_err_once("xencons: Illegal ring page indices");
+		return -EINVAL;
+	}
 
 	while ((sent < len) && ((prod - cons) < sizeof(intf->out)))
 		intf->out[MASK_XENCONS_IDX(prod++, intf->out)] = data[sent++];
@@ -114,7 +118,10 @@ static int domU_write_console(uint32_t vtermno, const char *data, int len)
 	 */
 	while (len) {
 		int sent = __write_console(cons, data, len);
-		
+
+		if (sent < 0)
+			return sent;
+
 		data += sent;
 		len -= sent;
 
@@ -138,7 +145,11 @@ static int domU_read_console(uint32_t vtermno, char *buf, int len)
 	cons = intf->in_cons;
 	prod = intf->in_prod;
 	mb();			/* get pointers before reading ring */
-	BUG_ON((prod - cons) > sizeof(intf->in));
+
+	if ((prod - cons) > sizeof(intf->in)) {
+		pr_err_once("xencons: Illegal ring page indices");
+		return -EINVAL;
+	}
 
 	while (cons != prod && recv < len)
 		buf[recv++] = intf->in[MASK_XENCONS_IDX(cons++, intf->in)];
-- 
2.26.2