Commit 900fdc45 authored by Richard Fitzgerald's avatar Richard Fitzgerald Committed by Petr Mladek
Browse files

lib: vsprintf: Fix handling of number field widths in vsscanf 



The existing code attempted to handle numbers by doing a strto[u]l(),
ignoring the field width, and then repeatedly dividing to extract the
field out of the full converted value. If the string contains a run of
valid digits longer than will fit in a long or long long, this would
overflow and no amount of dividing can recover the correct value.

This patch fixes vsscanf() to obey number field widths when parsing
the number.

A new _parse_integer_limit() is added that takes a limit for the number
of characters to parse. The number field conversion in vsscanf is changed
to use this new function.

If a number starts with a radix prefix, the field width  must be long
enough for at last one digit after the prefix. If not, it will be handled
like this:

 sscanf("0x4", "%1i", &i): i=0, scanning continues with the 'x'
 sscanf("0x4", "%2i", &i): i=0, scanning continues with the '4'

This is consistent with the observed behaviour of userland sscanf.

Note that this patch does NOT fix the problem of a single field value
overflowing the target type. So for example:

  sscanf("123456789abcdef", "%x", &i);

Will not produce the correct result because the value obviously overflows
INT_MAX. But sscanf will report a successful conversion.

Note that where a very large number is used to mean "unlimited", the value
INT_MAX is used for consistency with the behaviour of vsnprintf().

Signed-off-by: default avatarRichard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210514161206.30821-2-rf@opensource.cirrus.com
parent 11b3dda5

lib/kstrtox.c

+10 −3
Original line number Diff line number Diff line
@@ -39,20 +39,22 @@ const char *_parse_integer_fixup_radix(const char *s, unsigned int *base) 


/*

 * Convert non-negative integer string representation in explicitly given radix

 * to an integer.

 * to an integer. A maximum of max_chars characters will be converted.

 *

 * Return number of characters consumed maybe or-ed with overflow bit.

 * If overflow occurs, result integer (incorrect) is still returned.

 *

 * Don't you dare use this function.

 */

unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long *p)

unsigned int _parse_integer_limit(const char *s, unsigned int base, unsigned long long *p,

				  size_t max_chars)

{

	unsigned long long res;

	unsigned int rv;



	res = 0;

	rv = 0;

	while (1) {

	while (max_chars--) {

		unsigned int c = *s;

		unsigned int lc = c | 0x20; /* don't tolower() this line */

		unsigned int val;
@@ -82,6 +84,11 @@ unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long 
	return rv;

}



unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long *p)

{

	return _parse_integer_limit(s, base, p, INT_MAX);

}



static int _kstrtoull(const char *s, unsigned int base, unsigned long long *res)

{

	unsigned long long _res;

lib/kstrtox.h

+2 −0
Original line number Diff line number Diff line
@@ -4,6 +4,8 @@ 


#define KSTRTOX_OVERFLOW	(1U << 31)

const char *_parse_integer_fixup_radix(const char *s, unsigned int *base);

unsigned int _parse_integer_limit(const char *s, unsigned int base, unsigned long long *res,

				  size_t max_chars);

unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long *res);



#endif

lib/vsprintf.c

+48 −34
Original line number Diff line number Diff line
@@ -53,29 +53,43 @@ 
#include <linux/string_helpers.h>

#include "kstrtox.h"



/**

 * simple_strtoull - convert a string to an unsigned long long

 * @cp: The start of the string

 * @endp: A pointer to the end of the parsed string will be placed here

 * @base: The number base to use

 *

 * This function has caveats. Please use kstrtoull instead.

 */

unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base)

static unsigned long long simple_strntoull(const char *startp, size_t max_chars,

					   char **endp, unsigned int base)

{

	unsigned long long result;

	const char *cp;

	unsigned long long result = 0ULL;

	size_t prefix_chars;

	unsigned int rv;



	cp = _parse_integer_fixup_radix(cp, &base);

	rv = _parse_integer(cp, base, &result);

	cp = _parse_integer_fixup_radix(startp, &base);

	prefix_chars = cp - startp;

	if (prefix_chars < max_chars) {

		rv = _parse_integer_limit(cp, base, &result, max_chars - prefix_chars);

		/* FIXME */

		cp += (rv & ~KSTRTOX_OVERFLOW);

	} else {

		/* Field too short for prefix + digit, skip over without converting */

		cp = startp + max_chars;

	}



	if (endp)

		*endp = (char *)cp;



	return result;

}



/**

 * simple_strtoull - convert a string to an unsigned long long

 * @cp: The start of the string

 * @endp: A pointer to the end of the parsed string will be placed here

 * @base: The number base to use

 *

 * This function has caveats. Please use kstrtoull instead.

 */

unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base)

{

	return simple_strntoull(cp, INT_MAX, endp, base);

}

EXPORT_SYMBOL(simple_strtoull);



/**
@@ -109,6 +123,21 @@ 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)

{

	/*

	 * 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);

}



/**

 * simple_strtoll - convert a string to a signed long long

 * @cp: The start of the string
@@ -119,10 +148,7 @@ EXPORT_SYMBOL(simple_strtol); 
 */

long long simple_strtoll(const char *cp, char **endp, unsigned int base)

{

	if (*cp == '-')

		return -simple_strtoull(cp + 1, endp, base);



	return simple_strtoull(cp, endp, base);

	return simple_strntoll(cp, INT_MAX, endp, base);

}

EXPORT_SYMBOL(simple_strtoll);
@@ -3541,25 +3567,13 @@ int vsscanf(const char *buf, const char *fmt, va_list args) 
			break;



		if (is_sign)

			val.s = qualifier != 'L' ?

				simple_strtol(str, &next, base) :

				simple_strtoll(str, &next, base);

			val.s = simple_strntoll(str,

						field_width >= 0 ? field_width : INT_MAX,

						&next, base);

		else

			val.u = qualifier != 'L' ?

				simple_strtoul(str, &next, base) :

				simple_strtoull(str, &next, base);



		if (field_width > 0 && next - str > field_width) {

			if (base == 0)

				_parse_integer_fixup_radix(str, &base);

			while (next - str > field_width) {

				if (is_sign)

					val.s = div_s64(val.s, base);

				else

					val.u = div_u64(val.u, base);

				--next;

			}

		}

			val.u = simple_strntoull(str,

						 field_width >= 0 ? field_width : INT_MAX,

						 &next, base);



		switch (qualifier) {

		case 'H':	/* that's 'hh' in format */