From 70d2687d85c314963cf280759b23fd4573ff0d82 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Wed, 19 Oct 2016 20:17:16 -0400 Subject: [PATCH] fix integer overflow in float printf needed-precision computation if the requested precision is close to INT_MAX, adding LDBL_MANT_DIG/3+8 overflows. in practice the resulting undefined behavior manifests as a large negative result, which is then used to compute the new end pointer (z) with a wildly out-of-bounds value (more overflow, more undefined behavior). the end result is at least incorrect output and character count (return value); worse things do not seem to happen, but detailed analysis has not been done. this patch fixes the overflow by performing the intermediate computation as unsigned; after division by 9, the final result necessarily fits in int. --- src/stdio/vfprintf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c index e439a07a..cd17ad70 100644 --- a/src/stdio/vfprintf.c +++ b/src/stdio/vfprintf.c @@ -312,7 +312,7 @@ static int fmt_fp(FILE *f, long double y, int w, int p, int fl, int t) } while (e2<0) { uint32_t carry=0, *b; - int sh=MIN(9,-e2), need=1+(p+LDBL_MANT_DIG/3+8)/9; + int sh=MIN(9,-e2), need=1+(p+LDBL_MANT_DIG/3U+8)/9; for (d=a; d>sh) + carry; -- GitLab