linux-kernel - [PATCH 18/20] usb: gadget: f_midi: Manual replacement of the deprecated strlcpy() with return values

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Message-Id: <20210222151231.22572-19-romain.perier@gmail.com>
Date:   Mon, 22 Feb 2021 16:12:29 +0100
From:   Romain Perier <romain.perier@...il.com>
To:     Kees Cook <keescook@...omium.org>,
        kernel-hardening@...ts.openwall.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>
Cc:     Romain Perier <romain.perier@...il.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 18/20] usb: gadget: f_midi: Manual replacement of the deprecated strlcpy() with return values

The strlcpy() reads the entire source buffer first, it is dangerous if
the source buffer lenght is unbounded or possibility non NULL-terminated.
It can lead to linear read overflows, crashes, etc...

As recommended in the deprecated interfaces [1], it should be replaced
by strscpy.

This commit replaces all calls to strlcpy that handle the return values
by the corresponding strscpy calls with new handling of the return
values (as it is quite different between the two functions).

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy

Signed-off-by: Romain Perier <romain.perier@...il.com>
---
 drivers/usb/gadget/function/f_midi.c    |    4 ++--
 drivers/usb/gadget/function/f_printer.c |    8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
index 71a1a26e85c7..1f2b0d4309b4 100644
--- a/drivers/usb/gadget/function/f_midi.c
+++ b/drivers/usb/gadget/function/f_midi.c
@@ -1143,11 +1143,11 @@ F_MIDI_OPT(out_ports, true, MAX_PORTS);
 static ssize_t f_midi_opts_id_show(struct config_item *item, char *page)
 {
 	struct f_midi_opts *opts = to_f_midi_opts(item);
-	int result;
+	ssize_t result;
 
 	mutex_lock(&opts->lock);
 	if (opts->id) {
-		result = strlcpy(page, opts->id, PAGE_SIZE);
+		result = strscpy(page, opts->id, PAGE_SIZE);
 	} else {
 		page[0] = 0;
 		result = 0;
diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
index 61ce8e68f7a3..af83953e6770 100644
--- a/drivers/usb/gadget/function/f_printer.c
+++ b/drivers/usb/gadget/function/f_printer.c
@@ -1212,15 +1212,15 @@ static ssize_t f_printer_opts_pnp_string_show(struct config_item *item,
 					      char *page)
 {
 	struct f_printer_opts *opts = to_f_printer_opts(item);
-	int result = 0;
+	ssize_t result = 0;
 
 	mutex_lock(&opts->lock);
 	if (!opts->pnp_string)
 		goto unlock;
 
-	result = strlcpy(page, opts->pnp_string, PAGE_SIZE);
-	if (result >= PAGE_SIZE) {
-		result = PAGE_SIZE;
+	result = strscpy(page, opts->pnp_string, PAGE_SIZE);
+	if (result == -E2BIG) {
+		goto unlock;
 	} else if (page[result - 1] != '\n' && result + 1 < PAGE_SIZE) {
 		page[result++] = '\n';
 		page[result] = '\0';