36 lines
1.4 KiB
Diff
36 lines
1.4 KiB
Diff
From 70d2687d85c314963cf280759b23fd4573ff0d82 Mon Sep 17 00:00:00 2001
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From: Rich Felker <dalias@aerifal.cx>
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Date: Wed, 19 Oct 2016 20:17:16 -0400
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Subject: fix integer overflow in float printf needed-precision computation
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if the requested precision is close to INT_MAX, adding
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LDBL_MANT_DIG/3+8 overflows. in practice the resulting undefined
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behavior manifests as a large negative result, which is then used to
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compute the new end pointer (z) with a wildly out-of-bounds value
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(more overflow, more undefined behavior). the end result is at least
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incorrect output and character count (return value); worse things do
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not seem to happen, but detailed analysis has not been done.
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this patch fixes the overflow by performing the intermediate
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computation as unsigned; after division by 9, the final result
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necessarily fits in int.
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---
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src/stdio/vfprintf.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
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index e439a07..cd17ad7 100644
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--- a/src/stdio/vfprintf.c
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+++ b/src/stdio/vfprintf.c
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@@ -312,7 +312,7 @@ static int fmt_fp(FILE *f, long double y, int w, int p, int fl, int t)
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}
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while (e2<0) {
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uint32_t carry=0, *b;
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- int sh=MIN(9,-e2), need=1+(p+LDBL_MANT_DIG/3+8)/9;
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+ int sh=MIN(9,-e2), need=1+(p+LDBL_MANT_DIG/3U+8)/9;
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for (d=a; d<z; d++) {
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uint32_t rm = *d & (1<<sh)-1;
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*d = (*d>>sh) + carry;
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--
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cgit v0.11.2
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