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Sat, 10 Jun 2023 16:40:58 -0400 (EDT) From: Demi Marie Obenour To: Hans de Goede , Mauro Carvalho Chehab , Sakari Ailus , Greg Kroah-Hartman , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Lee Jones , Andy Lutomirski , Thomas Gleixner , Vincenzo Frascino , Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Andy Shevchenko , Rasmus Villemoes Cc: Demi Marie Obenour , linux-media@vger.kernel.org, linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, Linus Torvalds Subject: [PATCH v3 2/4] vsscanf(): Integer overflow is a conversion failure Date: Sat, 10 Jun 2023 16:40:42 -0400 Message-Id: <20230610204044.3653-3-demi@invisiblethingslab.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230610204044.3653-1-demi@invisiblethingslab.com> References: <20230610204044.3653-1-demi@invisiblethingslab.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,SPF_HELO_PASS, SPF_NONE,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1768350425372719424?= X-GMAIL-MSGID: =?utf-8?q?1768350425372719424?= sscanf() and friends currently ignore integer overflow, but this is a bad idea. It is much better to detect integer overflow errors and consider this a conversion failure. This implements Linus's suggestion of using '!' to treat integer overflow as wrapping. It does _not_ allow wrapping of unsigned conversions by default, though, as in at least some cases accepting negative numbers is _not_ intended. Suggested-By: Linus Torvalds Signed-off-by: Demi Marie Obenour --- lib/vsprintf.c | 90 ++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 69 insertions(+), 21 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 40f560959b169b4c4ac6154d658cfe76cfd0c5a6..9e53355c35b1d6260631868228ede1d178fe3325 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; @@ -70,11 +70,13 @@ static noinline unsigned long long simple_strntoull(const char *startp, size_t m prefix_chars = cp - startp; if (prefix_chars < max_chars) { rv = _parse_integer_limit(cp, base, &result, max_chars - prefix_chars); - /* FIXME */ + *overflow = !!(rv & KSTRTOX_OVERFLOW); cp += (rv & ~KSTRTOX_OVERFLOW); } else { /* Field too short for prefix + digit, skip over without converting */ cp = startp + max_chars; + /* Treat this as a conversion failure */ + *overflow = true; } if (endp) @@ -94,7 +96,9 @@ 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); + bool _placeholder; + + return simple_strntoull(cp, INT_MAX, endp, base, &_placeholder); } EXPORT_SYMBOL(simple_strtoull); @@ -130,18 +134,22 @@ 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; } /** @@ -154,7 +162,9 @@ static long long simple_strntoll(const char *cp, size_t max_chars, char **endp, */ long long simple_strtoll(const char *cp, char **endp, unsigned int base) { - return simple_strntoll(cp, INT_MAX, endp, base); + bool _placeholder; + + return simple_strntoll(cp, INT_MAX, endp, base, &_placeholder); } EXPORT_SYMBOL(simple_strtoll); @@ -3441,7 +3451,7 @@ 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, allow_overflow; while (*fmt) { /* skip any white space in format */ @@ -3464,6 +3474,9 @@ int vsscanf(const char *buf, const char *fmt, va_list args) break; ++fmt; + allow_overflow = *fmt == '!'; + fmt += (int)allow_overflow; + /* skip this conversion. * advance both strings to next white space */ @@ -3649,45 +3662,80 @@ 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) && !allow_overflow) + break; 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) && + !allow_overflow) + return num; *va_arg(args, signed char *) = val.s; - else + } else { + if (unlikely(val.u > UCHAR_MAX) && !allow_overflow) + return num; *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) && + !allow_overflow) + return num; *va_arg(args, short *) = val.s; - else + } else { + if (unlikely(val.u > USHRT_MAX) && !allow_overflow) + return num; *va_arg(args, unsigned short *) = val.u; + } break; case 'l': - if (is_sign) + if (is_sign) { + if (unlikely(val.s < LONG_MIN || val.s > LONG_MAX) && + !allow_overflow) + return num; *va_arg(args, long *) = val.s; - else + } else { + if (unlikely(val.u > ULONG_MAX) && !allow_overflow) + return num; *va_arg(args, unsigned long *) = val.u; + } break; case 'L': + /* No overflow check needed */ if (is_sign) *va_arg(args, long long *) = val.s; else *va_arg(args, unsigned long long *) = val.u; break; case 'z': - *va_arg(args, size_t *) = val.u; + if (is_sign) { + if (unlikely(val.s < SSIZE_MIN || val.s > SSIZE_MAX)) + return num; + *va_arg(args, ssize_t *) = val.s; + } else { + if (unlikely(val.u > SIZE_MAX) && !allow_overflow) + return num; + *va_arg(args, size_t *) = val.u; + } break; default: - if (is_sign) + if (is_sign) { + if (unlikely(val.s < INT_MIN || val.s > INT_MAX) && + !allow_overflow) + return num; *va_arg(args, int *) = val.s; - else + } else { + if (unlikely(val.u > UINT_MAX) && !allow_overflow) + return num; *va_arg(args, unsigned int *) = val.u; + } break; } num++;