| Message ID | 20210208140154.10964-2-rf@opensource.cirrus.com |
|---|---|
| State | New |
| Headers | show |
| Series | None | expand |
On Mon 2021-02-08 17:38:29, Richard Fitzgerald wrote: > On 08/02/2021 15:18, Andy Shevchenko wrote: > > On Mon, Feb 08, 2021 at 02:01:52PM +0000, Richard Fitzgerald wrote: > > > 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. > > > > > > -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; > > > unsigned int rv; > > > - cp = _parse_integer_fixup_radix(cp, &base); > > > - rv = _parse_integer(cp, base, &result); > > > + cp = _parse_integer_fixup_radix(startp, &base); > > > + if ((cp - startp) >= max_chars) { > > > + cp = startp + max_chars; > > > + goto out; > > > + } > > > + > > > + max_chars -= (cp - startp); > > > + rv = _parse_integer_limit(cp, base, &result, max_chars); > > > /* FIXME */ > > > cp += (rv & ~KSTRTOX_OVERFLOW); > > > +out: > > > if (endp) > > > *endp = (char *)cp; > > > return result; > > > } > > > > A nit-pick: What if we rewrite above as > > > > static unsigned long long simple_strntoull(const char *cp, size_t max_chars, > > char **endp, unsigned int base) > > { > > unsigned long long result = 0ULL; > > const char *startp = cp; > > unsigned int rv; > > size_t chars; > > > > cp = _parse_integer_fixup_radix(cp, &base); > > chars = cp - startp; > > if (chars >= max_chars) { > > /* We hit the limit */ > > cp = startp + max_chars; > > } else { > > rv = _parse_integer_limit(cp, base, &result, max_chars - chars); > > /* FIXME */ > > cp += (rv & ~KSTRTOX_OVERFLOW); > > } > > > > if (endp) > > *endp = (char *)cp; > > > > return result; > > } > > > > ... > > > I don't mind rewriting that code if you prefer that way. > I am used to working on other kernel subsytems where the preference is > to bail out on the error case so that the "normal" case flows without > nesting. Yeah. But in this case Andy's variant looks slightly better redable to me. ... > > > > > + val.s = simple_strntoll(str, > > > + field_width > 0 ? field_width : SIZE_MAX, > > > + &next, base); > > > > A nit-pick: Wouldn't be negative field_width "big enough" to just being used as > field_width is s16 so really should be sign-extended I guess that Andy just missed that it was a signed type. And it has to be because -1 means SIZE_MAX. > to make it "very > big". I think this would be less readable what the intention is and what > assumptions it is based on. There's a risk someone would look at > > (size_t)(long)field_width > > and think the (long) is redundant. > Perhaps change field_width to int? There I ask myself "if it can be an > int, why is it declared s16?" and worry there is something subtle in the > code. > > My personal preference is to avoid using tricks in code that isn't time > critical. I agree. Let's keep the check with signed type. > > is? Also, is field_width == 0 should be treated as "parse to the MAX"? filed_width == 0 actually means that no characters are read. I should return zero value. > > ... > > Earlier code terminates scanning if the width parsed from the format > string is <= 0. To make it clear what earlier code means. vsscanf() bail out earlier when field_width == 0. It is handled by this code: /* get field width */ field_width = -1; if (isdigit(*fmt)) { field_width = skip_atoi(&fmt); if (field_width <= 0) break; } > So field_width can only be -1 or > 0 here. But now you > point it out, that test would be better as field_width >= 0 ... so > it deals with 0 if it ever happened to sneak through to here > somehow. It might make sense to be proactive and change it to >= 0. But I would do it in a separate patch. The "< 0" condition matches the original code. Best Regards, Petr
On Thu 2021-02-11 13:55:26, Petr Mladek wrote: > On Mon 2021-02-08 17:38:29, Richard Fitzgerald wrote: > > On 08/02/2021 15:18, Andy Shevchenko wrote: > > > On Mon, Feb 08, 2021 at 02:01:52PM +0000, Richard Fitzgerald wrote: > > > A nit-pick: What if we rewrite above as > > > > > > static unsigned long long simple_strntoull(const char *cp, size_t max_chars, > > > char **endp, unsigned int base) > > > { > > > unsigned long long result = 0ULL; > > > const char *startp = cp; > > > unsigned int rv; > > > size_t chars; > > > > > > cp = _parse_integer_fixup_radix(cp, &base); > > > chars = cp - startp; > > > if (chars >= max_chars) { > > > /* We hit the limit */ > > > cp = startp + max_chars; > > > } else { > > > rv = _parse_integer_limit(cp, base, &result, max_chars - chars); > > > /* FIXME */ > > > cp += (rv & ~KSTRTOX_OVERFLOW); > > > } > > > > > > if (endp) > > > *endp = (char *)cp; > > > > > > return result; > > > } > > > > > > ... > > > > > > I don't mind rewriting that code if you prefer that way. > > I am used to working on other kernel subsytems where the preference is > > to bail out on the error case so that the "normal" case flows without > > nesting. > > Yeah. But in this case Andy's variant looks slightly better redable to me. > ... > > > > > > > > + val.s = simple_strntoll(str, > > > > + field_width > 0 ? field_width : SIZE_MAX, > > > > + &next, base); > > > > > > is? Also, is field_width == 0 should be treated as "parse to the MAX"? > > > > Earlier code terminates scanning if the width parsed from the format > > string is <= 0. > > > So field_width can only be -1 or > 0 here. But now you > > point it out, that test would be better as field_width >= 0 ... so > > it deals with 0 if it ever happened to sneak through to here > > somehow. > > It might make sense to be proactive and change it to >= 0. > But I would do it in a separate patch. The "< 0" condition > matches the original code. Ah, I have missed that you have already sent v6 where you did this change in the same patch. There is no need to resend it just because of this. I am going to look at v6. Best Regards, Petr
diff --git a/lib/kstrtox.c b/lib/kstrtox.c index a118b0b1e9b2..0fdd07a03564 100644 --- a/lib/kstrtox.c +++ b/lib/kstrtox.c @@ -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, SIZE_MAX); +} + static int _kstrtoull(const char *s, unsigned int base, unsigned long long *res) { unsigned long long _res; diff --git a/lib/kstrtox.h b/lib/kstrtox.h index 3b4637bcd254..158c400ca865 100644 --- a/lib/kstrtox.h +++ b/lib/kstrtox.h @@ -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 diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 28bb26cd1f67..1ede80c376b7 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -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; unsigned int rv; - cp = _parse_integer_fixup_radix(cp, &base); - rv = _parse_integer(cp, base, &result); + cp = _parse_integer_fixup_radix(startp, &base); + if ((cp - startp) >= max_chars) { + cp = startp + max_chars; + goto out; + } + + max_chars -= (cp - startp); + rv = _parse_integer_limit(cp, base, &result, max_chars); /* FIXME */ cp += (rv & ~KSTRTOX_OVERFLOW); +out: 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, SIZE_MAX, endp, base); +} EXPORT_SYMBOL(simple_strtoull); /** @@ -88,7 +102,7 @@ EXPORT_SYMBOL(simple_strtoull); */ unsigned long simple_strtoul(const char *cp, char **endp, unsigned int base) { - return simple_strtoull(cp, endp, base); + return simple_strntoull(cp, SIZE_MAX, endp, base); } EXPORT_SYMBOL(simple_strtoul); @@ -109,6 +123,19 @@ 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 we start with max_chars==1 and find a '-' prefix. + */ + 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 +146,7 @@ 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, SIZE_MAX, endp, base); } EXPORT_SYMBOL(simple_strtoll); @@ -3449,25 +3473,13 @@ 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 : SIZE_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 : SIZE_MAX, + &next, base); switch (qualifier) { case 'H': /* that's 'hh' in format */
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. Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com> --- Changed since v3: - Consistently use SIZE_MAX as the "infinity" value when passing to size_t arguments. - Use while-loop instead of for-loop in _parse_integer_limit(). - Keep the existing arguments for _parse_integer() on their original line. And the corresponding arguments to _parse_integer_limit() formatted/wrapped the same way as _parse_integer(). - Remove redundant check for (max_chars == 0) in simple_strntoull(). - Fixed "vsscanf" -> "vsscanf()" in commit message. --- lib/kstrtox.c | 13 ++++++-- lib/kstrtox.h | 2 ++ lib/vsprintf.c | 82 +++++++++++++++++++++++++++++--------------------- 3 files changed, 59 insertions(+), 38 deletions(-)