linux-kernel - [PATCH 06/12] scanf: fix type range overflow

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Date:	Fri, 8 May 2015 21:34:32 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, linux@...musvillemoes.dk
Subject: [PATCH 06/12] scanf: fix type range overflow

Fun fact:

	uint8_t val;
	sscanf("256", "%hhu", &val);

will return 1 and make val=0 (clearly bogus).

Userspace sscanf() reports 1 parsed value, returns incorrect value
but sets errno to ERANGE only for "%u" conversion and higher.
%hhu and %hu are left in the cold.

Having no way to report errno=ERANGE in kernel, don't report
successful parsing.

Patch allows to remove checks and switch to proper types
in several (most?) cases:

	grep -e 'scanf.*%[0-9]\+[dioux]' -n -r .

Such checks can be incorrect too -- checking for 3 digits with %3u
for parsing uint8_t is not enough.

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---
 lib/vsprintf.c | 45 ++++++++++++++++++++++++++++++++++-----------
 1 file changed, 34 insertions(+), 11 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 6509c54..58051b4 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2632,44 +2632,67 @@ 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) {
+				if (val.s != (signed char)val.s)
+					goto out;
 				*va_arg(args, signed char *) = val.s;
-			else
+			} else {
+				if (val.u != (unsigned char)val.u)
+					goto out;
 				*va_arg(args, unsigned char *) = val.u;
+			}
 			break;
 		case 'h':
-			if (is_sign)
+			if (is_sign) {
+				if (val.s != (short)val.s)
+					goto out;
 				*va_arg(args, short *) = val.s;
-			else
+			} else {
+				if (val.u != (unsigned short)val.u)
+					goto out;
 				*va_arg(args, unsigned short *) = val.u;
+			}
 			break;
 		case 'l':
-			if (is_sign)
+			if (is_sign) {
+				if (val.s != (long)val.s)
+					goto out;
 				*va_arg(args, long *) = val.s;
-			else
+			} else {
+				if (val.u != (unsigned long)val.u)
+					goto out;
 				*va_arg(args, unsigned long *) = val.u;
+			}
 			break;
 		case 'L':
-			if (is_sign)
+			if (is_sign) {
 				*va_arg(args, long long *) = val.s;
-			else
+			} else {
 				*va_arg(args, unsigned long long *) = val.u;
+			}
 			break;
 		case 'Z':
 		case 'z':
+			if (val.u != (size_t)val.u)
+				goto out;
 			*va_arg(args, size_t *) = val.u;
 			break;
 		default:
-			if (is_sign)
+			if (is_sign) {
+				if (val.s != (int)val.s)
+					goto out;
 				*va_arg(args, int *) = val.s;
-			else
+			} else {
+				if (val.u != (unsigned int)val.u)
+					goto out;
 				*va_arg(args, unsigned int *) = val.u;
+			}
 			break;
 		}
 		num++;
 		str += len;
 	}
-
+out:
 	return num;
 }
 EXPORT_SYMBOL(vsscanf);
-- 
2.0.4

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