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

[ Upstream commit 900fdc4573766dd43b847b4f54bd4a1ee2bc7360 ]

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: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210514161206.30821-2-rf@opensource.cirrus.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Richard Fitzgerald 2021-05-14 17:12:04 +01:00 committed by Greg Kroah-Hartman
parent 865c6e210b
commit e846c2821c
3 changed files with 60 additions and 37 deletions

View File

@ -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 * 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. * Return number of characters consumed maybe or-ed with overflow bit.
* If overflow occurs, result integer (incorrect) is still returned. * If overflow occurs, result integer (incorrect) is still returned.
* *
* Don't you dare use this function. * 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 long long res;
unsigned int rv; unsigned int rv;
res = 0; res = 0;
rv = 0; rv = 0;
while (1) { while (max_chars--) {
unsigned int c = *s; unsigned int c = *s;
unsigned int lc = c | 0x20; /* don't tolower() this line */ unsigned int lc = c | 0x20; /* don't tolower() this line */
unsigned int val; unsigned int val;
@ -82,6 +84,11 @@ unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long
return rv; 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) static int _kstrtoull(const char *s, unsigned int base, unsigned long long *res)
{ {
unsigned long long _res; unsigned long long _res;

View File

@ -4,6 +4,8 @@
#define KSTRTOX_OVERFLOW (1U << 31) #define KSTRTOX_OVERFLOW (1U << 31)
const char *_parse_integer_fixup_radix(const char *s, unsigned int *base); 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); unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long *res);
#endif #endif

View File

@ -50,6 +50,31 @@
#include <linux/string_helpers.h> #include <linux/string_helpers.h>
#include "kstrtox.h" #include "kstrtox.h"
static unsigned long long simple_strntoull(const char *startp, size_t max_chars,
char **endp, unsigned int base)
{
const char *cp;
unsigned long long result = 0ULL;
size_t prefix_chars;
unsigned int rv;
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 * simple_strtoull - convert a string to an unsigned long long
* @cp: The start of the string * @cp: The start of the string
@ -60,18 +85,7 @@
*/ */
unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base) unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base)
{ {
unsigned long long result; return simple_strntoull(cp, INT_MAX, endp, base);
unsigned int rv;
cp = _parse_integer_fixup_radix(cp, &base);
rv = _parse_integer(cp, base, &result);
/* FIXME */
cp += (rv & ~KSTRTOX_OVERFLOW);
if (endp)
*endp = (char *)cp;
return result;
} }
EXPORT_SYMBOL(simple_strtoull); EXPORT_SYMBOL(simple_strtoull);
@ -106,6 +120,21 @@ long simple_strtol(const char *cp, char **endp, unsigned int base)
} }
EXPORT_SYMBOL(simple_strtol); 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 * simple_strtoll - convert a string to a signed long long
* @cp: The start of the string * @cp: The start of the string
@ -116,10 +145,7 @@ EXPORT_SYMBOL(simple_strtol);
*/ */
long long simple_strtoll(const char *cp, char **endp, unsigned int base) long long simple_strtoll(const char *cp, char **endp, unsigned int base)
{ {
if (*cp == '-') return simple_strntoll(cp, INT_MAX, endp, base);
return -simple_strtoull(cp + 1, endp, base);
return simple_strtoull(cp, endp, base);
} }
EXPORT_SYMBOL(simple_strtoll); EXPORT_SYMBOL(simple_strtoll);
@ -3343,25 +3369,13 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
break; break;
if (is_sign) if (is_sign)
val.s = qualifier != 'L' ? val.s = simple_strntoll(str,
simple_strtol(str, &next, base) : field_width >= 0 ? field_width : INT_MAX,
simple_strtoll(str, &next, base); &next, base);
else else
val.u = qualifier != 'L' ? val.u = simple_strntoull(str,
simple_strtoul(str, &next, base) : field_width >= 0 ? field_width : INT_MAX,
simple_strtoull(str, &next, base); &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;
}
}
switch (qualifier) { switch (qualifier) {
case 'H': /* that's 'hh' in format */ case 'H': /* that's 'hh' in format */