[release-branch.go1.17] math/big: prevent overflow in (*Rat).SetString

Credit to rsc@ for the original patch.

Thanks to the OSS-Fuzz project for discovering this
issue and to Emmanuel Odeke (@odeke_et) for reporting it.

Updates #50699
Fixes #50701
Fixes CVE-2022-23772

Change-Id: I590395a3d55689625390cf1e58f5f40623b26ee5
Reviewed-on: https://go-review.googlesource.com/c/go/+/379537
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: Julie Qiu <julie@golang.org>
(cherry picked from commit ad345c265916bbf6c646865e4642eafce6d39e78)
Reviewed-on: https://go-review.googlesource.com/c/go/+/381336
Reviewed-by: Filippo Valsorda <filippo@golang.org>

diff --git a/src/math/big/ratconv.go b/src/math/big/ratconv.go
index ac3c8bd11f8a86756c7753c72d0454a0b9132937..90053a9c81d3b8c0fd697b4937d001a193344c93 100644 (file)
--- a/src/math/big/ratconv.go
+++ b/src/math/big/ratconv.go
@@ -169,6 +169,11 @@ func (z *Rat) SetString(s string) (*Rat, bool) {
                n := exp5
                if n < 0 {
                        n = -n
+                       if n < 0 {
+                               // This can occur if -n overflows. -(-1 << 63) would become
+                               // -1 << 63, which is still negative.
+                               return nil, false
+                       }
                }
                if n > 1e6 {
                        return nil, false // avoid excessively large exponents

diff --git a/src/math/big/ratconv_test.go b/src/math/big/ratconv_test.go
index 15d206cb386ab41dd0e79c2e5e01869413158763..e55e655718984abe1957cf3f521c602ca9393b11 100644 (file)
--- a/src/math/big/ratconv_test.go
+++ b/src/math/big/ratconv_test.go
@@ -104,6 +104,7 @@ var setStringTests = []StringTest{
        {in: "4/3/"},
        {in: "4/3."},
        {in: "4/"},
+       {in: "13e-9223372036854775808"}, // CVE-2022-23772
 
        // valid
        {"0", "0", true},