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- From 70d2687d85c314963cf280759b23fd4573ff0d82 Mon Sep 17 00:00:00 2001
- From: Rich Felker <[email protected]>
- Date: Wed, 19 Oct 2016 20:17:16 -0400
- Subject: 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 e439a07..cd17ad7 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<z; d++) {
- uint32_t rm = *d & (1<<sh)-1;
- *d = (*d>>sh) + carry;
- --
- cgit v0.11.2
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