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authorRich Felker <dalias@aerifal.cx>2016-10-19 20:17:16 -0400
committerRich Felker <dalias@aerifal.cx>2016-10-19 20:17:16 -0400
commit70d2687d85c314963cf280759b23fd4573ff0d82 (patch)
treedbbd4b169245294bee78e30f33e1cc22c519be3d /src/stdio
parentaee6abb2400b9a955c2b41166db1c22f63ad42ef (diff)
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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.
Diffstat (limited to 'src/stdio')
-rw-r--r--src/stdio/vfprintf.c2
1 files changed, 1 insertions, 1 deletions
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<z; d++) {
uint32_t rm = *d & (1<<sh)-1;
*d = (*d>>sh) + carry;