From 167dfe9672c116b315e72e57a55c7769f180dffa Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Thu, 20 Oct 2016 00:22:09 -0400 Subject: fix integer overflows and uncaught EOVERFLOW in printf core this patch fixes a large number of missed internal signed-overflow checks and errors in determining when the return value (output length) would exceed INT_MAX, which should result in EOVERFLOW. some of the issues fixed were reported by Alexander Cherepanov; others were found in subsequent review of the code. aside from the signed overflows being undefined behavior, the following specific bugs were found to exist in practice: - overflows computing length of floating point formats with huge explicit precisions, integer formats with prefix characters and huge explicit precisions, or string arguments or format strings longer than INT_MAX, resulted in wrong return value and wrong %n results. - literal width and precision values outside the range of int were misinterpreted, yielding wrong behavior in at least one well-defined case: string formats with precision greater than INT_MAX were sometimes truncated. - in cases where EOVERFLOW is produced, incorrect values could be written for %n specifiers past the point of exceeding INT_MAX. in addition to fixing these bugs, we now stop producing output immediately when output length would exceed INT_MAX, rather than continuing and returning an error only at the end. --- src/stdio/vfwprintf.c | 63 +++++++++++++++++++++++++++++++-------------------- 1 file changed, 39 insertions(+), 24 deletions(-) (limited to 'src/stdio/vfwprintf.c') diff --git a/src/stdio/vfwprintf.c b/src/stdio/vfwprintf.c index f9f1ecfd..b8fff208 100644 --- a/src/stdio/vfwprintf.c +++ b/src/stdio/vfwprintf.c @@ -154,8 +154,10 @@ static void out(FILE *f, const wchar_t *s, size_t l) static int getint(wchar_t **s) { int i; - for (i=0; iswdigit(**s); (*s)++) - i = 10*i + (**s-'0'); + for (i=0; iswdigit(**s); (*s)++) { + if (i > INT_MAX/10U || **s-'0' > INT_MAX-10*i) i = -1; + else i = 10*i + (**s-'0'); + } return i; } @@ -168,8 +170,8 @@ static const char sizeprefix['y'-'a'] = { static int wprintf_core(FILE *f, const wchar_t *fmt, va_list *ap, union arg *nl_arg, int *nl_type) { wchar_t *a, *z, *s=(wchar_t *)fmt; - unsigned l10n=0, litpct, fl; - int w, p; + unsigned l10n=0, fl; + int w, p, xp; union arg arg; int argpos; unsigned st, ps; @@ -181,20 +183,19 @@ static int wprintf_core(FILE *f, const wchar_t *fmt, va_list *ap, union arg *nl_ wchar_t wc; for (;;) { + /* This error is only specified for snprintf, but since it's + * unspecified for other forms, do the same. Stop immediately + * on overflow; otherwise %n could produce wrong results. */ + if (l > INT_MAX - cnt) goto overflow; + /* Update output count, end loop when fmt is exhausted */ - if (cnt >= 0) { - if (l > INT_MAX - cnt) { - if (!ferror(f)) errno = EOVERFLOW; - cnt = -1; - } else cnt += l; - } + cnt += l; if (!*s) break; /* Handle literal text and %% format specifiers */ for (a=s; *s && *s!='%'; s++); - litpct = wcsspn(s, L"%")/2; /* Optimize %%%% runs */ - z = s+litpct; - s += 2*litpct; + for (z=s; s[0]=='%' && s[1]=='%'; z++, s+=2); + if (z-a > INT_MAX-cnt) goto overflow; l = z-a; if (f) out(f, a, l); if (l) continue; @@ -222,9 +223,9 @@ static int wprintf_core(FILE *f, const wchar_t *fmt, va_list *ap, union arg *nl_ } else if (!l10n) { w = f ? va_arg(*ap, int) : 0; s++; - } else return -1; + } else goto inval; if (w<0) fl|=LEFT_ADJ, w=-w; - } else if ((w=getint(&s))<0) return -1; + } else if ((w=getint(&s))<0) goto overflow; /* Read precision */ if (*s=='.' && s[1]=='*') { @@ -235,24 +236,29 @@ static int wprintf_core(FILE *f, const wchar_t *fmt, va_list *ap, union arg *nl_ } else if (!l10n) { p = f ? va_arg(*ap, int) : 0; s+=2; - } else return -1; + } else goto inval; + xp = (p>=0); } else if (*s=='.') { s++; p = getint(&s); - } else p = -1; + xp = 1; + } else { + p = -1; + xp = 0; + } /* Format specifier state machine */ st=0; do { - if (OOB(*s)) return -1; + if (OOB(*s)) goto inval; ps=st; st=states[st]S(*s++); } while (st-1=0) return -1; + if (argpos>=0) goto inval; } else { if (argpos>=0) nl_type[argpos]=st, arg=nl_arg[argpos]; else if (f) pop_arg(&arg, st, ap); @@ -285,8 +291,9 @@ static int wprintf_core(FILE *f, const wchar_t *fmt, va_list *ap, union arg *nl_ continue; case 'S': a = arg.p; - z = wmemchr(a, 0, p); - if (z) p=z-a; + z = a + wcsnlen(a, p<0 ? INT_MAX : p); + if (p<0 && *z) goto overflow; + p = z-a; if (w0; bs+=i, l++); + for (i=l=0; l<(p<0?INT_MAX:p) && (i=mbtowc(&wc, bs, MB_LEN_MAX))>0; bs+=i, l++); if (i<0) return -1; + if (p<0 && *bs) goto overflow; p=l; if (w