libcrypto: fix leak in BN_mpi2bn()

[Tobias Heider]

If ain == NULL then a points to newly malloced memory which should be
freed when BN_bin2bn() fails.

ok?

Index: bn/bn_mpi.c
===================================================================
RCS file: /cvs/src/lib/libcrypto/bn/bn_mpi.c,v
retrieving revision 1.8
diff -u -p -r1.8 bn_mpi.c
--- bn/bn_mpi.c 29 Jan 2017 17:49:22 -0000      1.8
+++ bn/bn_mpi.c 8 Nov 2022 17:30:33 -0000
@@ -121,8 +121,11 @@ BN_mpi2bn(const unsigned char *d, int n,
        d += 4;
        if ((*d) & 0x80)
                neg = 1;
-       if (BN_bin2bn(d, (int)len, a) == NULL)
+       if (BN_bin2bn(d, (int)len, a) == NULL) {
+               if (ain == NULL)
+                       BN_free(a);
                return (NULL);
+       }
        a->neg = neg;
        if (neg) {
                BN_clear_bit(a, BN_num_bits(a) - 1);