----- Ursprüngliche Mail -----

Von: "Christoph Hellwig" [off-list ref]
[Adding Richard and Linus as they're having another overflow checking
discussion and we should probably merge those]

Thx for letting me know!
 

On Fri, Jun 09, 2023 at 10:57:57PM -0400, Demi Marie Obenour wrote:

quoted

Userspace sets errno to ERANGE, but the kernel can't do that.

That seems like a very parse commit log, and also kinda besides
the point - the kernel always returns error in-line and not through
errno.  I think you need to document here why we want to do the
overflow checking (not that I doubt it, but it really needs to be
in the commit message).

Leaving the rest of the quote here for the new arrivals.

quoted

Signed-off-by: Demi Marie Obenour <redacted>
---
 include/linux/limits.h          |  1 +
 include/linux/mfd/wl1273-core.h |  3 --
 include/vdso/limits.h           |  3 ++
 lib/vsprintf.c                  | 80 ++++++++++++++++++++++++---------
 4 files changed, 63 insertions(+), 24 deletions(-)

diff --git a/include/linux/limits.h b/include/linux/limits.h

index
f6bcc936901071f496e3e85bb6e1d93905b12e32..8f7fd85b41fb46e6992d9e5912da00424119227a
100644

--- a/include/linux/limits.h
+++ b/include/linux/limits.h

@@ -8,6 +8,7 @@
 
 #define SIZE_MAX	(~(size_t)0)
 #define SSIZE_MAX	((ssize_t)(SIZE_MAX >> 1))
+#define SSIZE_MIN	(-SSIZE_MAX - 1)
 #define PHYS_ADDR_MAX	(~(phys_addr_t)0)
 
 #define U8_MAX		((u8)~0U)

diff --git a/include/linux/mfd/wl1273-core.h b/include/linux/mfd/wl1273-core.h

index
c28cf76d5c31ee1c94a9319a2e2d318bf00283a6..b81a229135ed9f756c749122a8341816031c8311
100644

--- a/include/linux/mfd/wl1273-core.h
+++ b/include/linux/mfd/wl1273-core.h

@@ -204,9 +204,6 @@
 				 WL1273_IS2_TRI_OPT | \
 				 WL1273_IS2_RATE_48K)
 
-#define SCHAR_MIN (-128)
-#define SCHAR_MAX 127
-
 #define WL1273_FR_EVENT			BIT(0)
 #define WL1273_BL_EVENT			BIT(1)
 #define WL1273_RDS_EVENT		BIT(2)

diff --git a/include/vdso/limits.h b/include/vdso/limits.h

index
0197888ad0e00b2f853d3f25ffa764f61cca7385..0cad0a2490e5efc194d874025eb3e3b846a5c7b4
100644

--- a/include/vdso/limits.h
+++ b/include/vdso/limits.h

@@ -2,6 +2,9 @@
 #ifndef __VDSO_LIMITS_H
 #define __VDSO_LIMITS_H
 
+#define UCHAR_MAX	((unsigned char)~0U)
+#define SCHAR_MAX	((signed char)(UCHAR_MAX >> 1))
+#define SCHAR_MIN	((signed char)(-SCHAR_MAX - 1))
 #define USHRT_MAX	((unsigned short)~0U)
 #define SHRT_MAX	((short)(USHRT_MAX >> 1))
 #define SHRT_MIN	((short)(-SHRT_MAX - 1))

diff --git a/lib/vsprintf.c b/lib/vsprintf.c

index
a60d348efb276d66ca07fe464883408df7fdab97..9846d2385f5b9e8f3945a5664d81047e97cf10d5
100644

--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c

@@ -59,7 +59,7 @@
 bool no_hash_pointers __ro_after_init;
 EXPORT_SYMBOL_GPL(no_hash_pointers);
 
-static noinline unsigned long long simple_strntoull(const char *startp, size_t

max_chars, char **endp, unsigned int base)
+static noinline unsigned long long simple_strntoull(const char *startp, size_t
max_chars, char **endp, unsigned int base, bool *overflow)
 {
 	const char *cp;
 	unsigned long long result = 0ULL;

@@ -71,6 +71,8 @@ static noinline unsigned long long simple_strntoull(const char

*startp, size_t m
 	if (prefix_chars < max_chars) {
 		rv = _parse_integer_limit(cp, base, &result, max_chars - prefix_chars);
 		/* FIXME */
+		if (overflow)
+			*overflow = !!(rv & KSTRTOX_OVERFLOW);
 		cp += (rv & ~KSTRTOX_OVERFLOW);
 	} else {
 		/* Field too short for prefix + digit, skip over without converting */

@@ -94,7 +96,7 @@ static noinline unsigned long long simple_strntoull(const char

*startp, size_t m
 noinline
 unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int
 base)
 {
-	return simple_strntoull(cp, INT_MAX, endp, base);
+	return simple_strntoull(cp, INT_MAX, endp, base, NULL);
 }
 EXPORT_SYMBOL(simple_strtoull);
 

@@ -130,18 +132,22 @@ long simple_strtol(const char *cp, char **endp, unsigned

int base)
 EXPORT_SYMBOL(simple_strtol);
 
 static long long simple_strntoll(const char *cp, size_t max_chars, char **endp,
-				 unsigned int base)
+				 unsigned int base, bool *overflow)
 {
+	unsigned long long minand;
+	bool negate;
+
 	/*
 	 * simple_strntoull() safely handles receiving max_chars==0 in the
 	 * case cp[0] == '-' && max_chars == 1.
 	 * If max_chars == 0 we can drop through and pass it to simple_strntoull()
 	 * and the content of *cp is irrelevant.
 	 */
-	if (*cp == '-' && max_chars > 0)
-		return -simple_strntoull(cp + 1, max_chars - 1, endp, base);
-
-	return simple_strntoull(cp, max_chars, endp, base);
+	negate = *cp == '-' && max_chars > 0;
+	minand = simple_strntoull(cp + negate, max_chars - negate, endp, base,
overflow);
+	if (minand > (unsigned long long)LONG_MAX + negate)
+		*overflow = true;
+	return negate ? -minand : minand;
 }
 
 static noinline_for_stack

@@ -3427,7 +3433,7 @@ int vsscanf(const char *buf, const char *fmt, va_list

args)
 		unsigned long long u;
 	} val;
 	s16 field_width;
-	bool is_sign;
+	bool is_sign, overflow;
 
 	while (*fmt) {
 		/* skip any white space in format */

@@ -3635,45 +3641,77 @@ int vsscanf(const char *buf, const char *fmt, va_list

args)
 		if (is_sign)
 			val.s = simple_strntoll(str,
 						field_width >= 0 ? field_width : INT_MAX,
-						&next, base);
+						&next, base, &overflow);
 		else
 			val.u = simple_strntoull(str,
 						 field_width >= 0 ? field_width : INT_MAX,
-						 &next, base);
+						 &next, base, &overflow);
+		if (unlikely(overflow))
+			return -ERANGE;
 
 		switch (qualifier) {
 		case 'H':	/* that's 'hh' in format */
-			if (is_sign)
+			if (is_sign) {
+				if (unlikely(val.s < SCHAR_MIN || val.s > SCHAR_MAX))
+					return -ERANGE;
 				*va_arg(args, signed char *) = val.s;
-			else
+			} else {
+				if (unlikely(val.u > UCHAR_MAX))
+					return -ERANGE;
 				*va_arg(args, unsigned char *) = val.u;
+			}
 			break;
 		case 'h':
-			if (is_sign)
+			if (is_sign) {
+				if (unlikely(val.s < SHRT_MIN || val.s > SHRT_MAX))
+					return -ERANGE;

Returning a negative value here will break many existing in-kernel users.
Most users just check for the number of matched elements.

Linus' idea was returning 0 upon overflow (nothing matched) and allowing
overflows (if really needed) by adding a new format string qualifier "!".
e.g. "%!d".

Thanks,
//richard