linux-hardening - [RFC PATCH 1/1] vsprintf: Warn on integer scanning overflows

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Date:   Thu,  8 Jun 2023 00:37:55 +0200
From:   Richard Weinberger <richard@....at>
To:     linux-hardening@...r.kernel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org, Richard Weinberger <richard@....at>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>
Subject: [RFC PATCH 1/1] vsprintf: Warn on integer scanning overflows

The scanf function family has no way to indicate overflows
while scanning. As consequence users of these function have to make
sure their input cannot cause an overflow.
Since this is not always the case add WARN_ON_ONCE() guards to
trigger a warning upon an overflow.

Signed-off-by: Richard Weinberger <richard@....at>
---
 lib/vsprintf.c | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 40f560959b169..3d8d751306cdc 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -70,6 +70,7 @@ static noinline unsigned long long simple_strntoull(const char *startp, size_t m
 	prefix_chars = cp - startp;
 	if (prefix_chars < max_chars) {
 		rv = _parse_integer_limit(cp, base, &result, max_chars - prefix_chars);
+		WARN_ON_ONCE(rv & KSTRTOX_OVERFLOW);
 		/* FIXME */
 		cp += (rv & ~KSTRTOX_OVERFLOW);
 	} else {
@@ -3657,22 +3658,34 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
 
 		switch (qualifier) {
 		case 'H':	/* that's 'hh' in format */
-			if (is_sign)
+			if (is_sign) {
+				WARN_ON_ONCE(val.s > 127);
+				WARN_ON_ONCE(val.s < -128);
 				*va_arg(args, signed char *) = val.s;
-			else
+			} else {
+				WARN_ON_ONCE(val.u > 255);
 				*va_arg(args, unsigned char *) = val.u;
+			}
 			break;
 		case 'h':
-			if (is_sign)
+			if (is_sign) {
+				WARN_ON_ONCE(val.s > SHRT_MAX);
+				WARN_ON_ONCE(val.s < SHRT_MIN);
 				*va_arg(args, short *) = val.s;
-			else
+			} else {
+				WARN_ON_ONCE(val.u > USHRT_MAX);
 				*va_arg(args, unsigned short *) = val.u;
+			}
 			break;
 		case 'l':
-			if (is_sign)
+			if (is_sign) {
+				WARN_ON_ONCE(val.s > LONG_MAX);
+				WARN_ON_ONCE(val.s < LONG_MIN);
 				*va_arg(args, long *) = val.s;
-			else
+			} else {
+				WARN_ON_ONCE(val.u > ULONG_MAX);
 				*va_arg(args, unsigned long *) = val.u;
+			}
 			break;
 		case 'L':
 			if (is_sign)
@@ -3684,10 +3697,14 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
 			*va_arg(args, size_t *) = val.u;
 			break;
 		default:
-			if (is_sign)
+			if (is_sign) {
+				WARN_ON_ONCE(val.s > INT_MAX);
+				WARN_ON_ONCE(val.s < INT_MIN);
 				*va_arg(args, int *) = val.s;
-			else
+			} else {
+				WARN_ON_ONCE(val.u > UINT_MAX);
 				*va_arg(args, unsigned int *) = val.u;
+			}
 			break;
 		}
 		num++;
-- 
2.35.3