From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751387AbWFTXsw (ORCPT ); Tue, 20 Jun 2006 19:48:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751866AbWFTXsw (ORCPT ); Tue, 20 Jun 2006 19:48:52 -0400 Received: from gw.goop.org ([64.81.55.164]:24008 "EHLO mail.goop.org") by vger.kernel.org with ESMTP id S1751387AbWFTXsv (ORCPT ); Tue, 20 Jun 2006 19:48:51 -0400 Message-ID: <44988965.9010906@goop.org> Date: Tue, 20 Jun 2006 16:48:53 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 1.5.0.4 (X11/20060613) MIME-Version: 1.0 To: Linux Kernel Mailing List CC: Andrew Morton , Christian Limpach , Chris Wright , Jeremy Fitzhardinge Subject: [PATCH] Fix bounds check in vsnprintf, to allow for a 0 size and NULL buffer Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: Jeremy Fitzhardinge This change allows callers to use a 0-byte buffer and a NULL buffer pointer with vsnprintf, so it can be used to determine how large the resulting formatted string will be. Previously the code effectively treated a size of 0 as a size of 4G (on 32-bit systems), with other checks preventing it from actually trying to emit the string - but the terminal \0 would still be written, which would crash if the buffer is NULL. This change changes the boundary check so that 'end' points to the putative location of the terminal '\0', which is only written if size > 0. vsnprintf still allows the buffer size to be set very large, to allow unbounded buffer sizes (to implement sprintf, etc). Signed-off-by: Jeremy Fitzhardinge Signed-off-by: Chris Wright --- lib/vsprintf.c | 67 ++++++++++++++++++++++++++++---------------------------- 1 file changed, 34 insertions(+), 33 deletions(-) diff -r 509769aa6636 lib/vsprintf.c --- a/lib/vsprintf.c Tue Jun 20 16:40:33 2006 -0700 +++ b/lib/vsprintf.c Tue Jun 20 16:47:51 2006 -0700 @@ -187,49 +187,49 @@ static char * number(char * buf, char * size -= precision; if (!(type&(ZEROPAD+LEFT))) { while(size-->0) { - if (buf <= end) + if (buf < end) *buf = ' '; ++buf; } } if (sign) { - if (buf <= end) + if (buf < end) *buf = sign; ++buf; } if (type & SPECIAL) { if (base==8) { - if (buf <= end) + if (buf < end) *buf = '0'; ++buf; } else if (base==16) { - if (buf <= end) + if (buf < end) *buf = '0'; ++buf; - if (buf <= end) + if (buf < end) *buf = digits[33]; ++buf; } } if (!(type & LEFT)) { while (size-- > 0) { - if (buf <= end) + if (buf < end) *buf = c; ++buf; } } while (i < precision--) { - if (buf <= end) + if (buf < end) *buf = '0'; ++buf; } while (i-- > 0) { - if (buf <= end) + if (buf < end) *buf = tmp[i]; ++buf; } while (size-- > 0) { - if (buf <= end) + if (buf < end) *buf = ' '; ++buf; } @@ -272,7 +272,8 @@ int vsnprintf(char *buf, size_t size, co /* 'z' changed to 'Z' --davidm 1/25/99 */ /* 't' added for ptrdiff_t */ - /* Reject out-of-range values early */ + /* Reject out-of-range values early. Large positive sizes are + used for unknown buffer sizes. */ if (unlikely((int) size < 0)) { /* There can be only one.. */ static int warn = 1; @@ -282,16 +283,17 @@ int vsnprintf(char *buf, size_t size, co } str = buf; - end = buf + size - 1; - - if (end < buf - 1) { - end = ((void *) -1); - size = end - buf + 1; + end = buf + size; + + /* Make sure end is always >= buf */ + if (end < buf) { + end = ((void *) ~0ull); + size = end - buf; } for (; *fmt ; ++fmt) { if (*fmt != '%') { - if (str <= end) + if (str < end) *str = *fmt; ++str; continue; @@ -357,17 +359,17 @@ int vsnprintf(char *buf, size_t size, co case 'c': if (!(flags & LEFT)) { while (--field_width > 0) { - if (str <= end) + if (str < end) *str = ' '; ++str; } } c = (unsigned char) va_arg(args, int); - if (str <= end) + if (str < end) *str = c; ++str; while (--field_width > 0) { - if (str <= end) + if (str < end) *str = ' '; ++str; } @@ -382,18 +384,18 @@ int vsnprintf(char *buf, size_t size, co if (!(flags & LEFT)) { while (len < field_width--) { - if (str <= end) + if (str < end) *str = ' '; ++str; } } for (i = 0; i < len; ++i) { - if (str <= end) + if (str < end) *str = *s; ++str; ++s; } while (len < field_width--) { - if (str <= end) + if (str < end) *str = ' '; ++str; } @@ -426,7 +428,7 @@ int vsnprintf(char *buf, size_t size, co continue; case '%': - if (str <= end) + if (str < end) *str = '%'; ++str; continue; @@ -449,11 +451,11 @@ int vsnprintf(char *buf, size_t size, co break; default: - if (str <= end) + if (str < end) *str = '%'; ++str; if (*fmt) { - if (str <= end) + if (str < end) *str = *fmt; ++str; } else { @@ -483,14 +485,13 @@ int vsnprintf(char *buf, size_t size, co str = number(str, end, num, base, field_width, precision, flags); } - if (str <= end) - *str = '\0'; - else if (size > 0) - /* don't write out a null byte if the buf size is zero */ - *end = '\0'; - /* the trailing null byte doesn't count towards the total - * ++str; - */ + if (size > 0) { + if (str < end) + *str = '\0'; + else + *end = '\0'; + } + /* the trailing null byte doesn't count towards the total */ return str-buf; }