Merge pull request fortanix#339 from fortanix/francisco/fips-rsadp-bounds

Add ciphertext check for RSADP

Author: Taowyoo

mbedtls/src/pk/mod.rs

@@ -17,6 +17,7 @@ use crate::hash::Type as MdType;
 use crate::private::UnsafeFrom;
 use crate::rng::Random;
 use core::convert::TryInto;
+use core::ops::Sub;
 use core::ptr;
 
 use byteorder::{BigEndian, ByteOrder};
@@ -691,6 +692,13 @@ impl Pk {
                     return Err(Error::RsaOutputTooLarge);
                 }
 
+                // Don't process outside of {2, ..., n-2}
+                let nm1 = self.rsa_public_modulus()?.sub(&Mpi::new(1)?)?;
+                let c_mpi = Mpi::from_binary(cipher)?;
+                if c_mpi <= Mpi::new(1).unwrap() || c_mpi >= nm1 {
+                    return Err(Error::MpiBadInputData);
+                }
+
                 unsafe {
                     rsa_private(ctx, Some(F::call), rng.data_ptr(), cipher.as_ptr(), plain.as_mut_ptr()).into_result()?;
                 };
@@ -1023,6 +1031,7 @@ mod tests {
     use super::*;
     use crate::hash::{MdInfo, Type};
     use crate::pk::Type as PkType;
+    use core::ops::Sub;
 
     // This is test data that must match library output *exactly*
     const TEST_PEM: &'static str = "-----BEGIN RSA PRIVATE KEY-----
@@ -1470,4 +1479,38 @@ iy6KC991zzvaWY/Ys+q/84Afqa+0qJKQnPuy/7F5GkVdQA/lfbhi
         assert!(pk.custom_public_key().is_err());
         assert!(pk.custom_private_key().is_err());
     }
+
+    #[test]
+    fn fips_rsadp_bounds() {
+        let rng = &mut crate::test_support::rand::test_rng();
+        let (bitlen, exp) = (2048, 0x10001);
+        let mut pk = Pk::generate_rsa(rng, bitlen, exp).unwrap();
+        pk.set_options(Options::Rsa {
+            padding: RsaPadding::None,
+        });
+
+        const LEN: usize = 256;
+
+        // Decrypting anything out of {2, n-2} should fail
+        let expected_err = Error::MpiBadInputData;
+
+        let mut pt = [0x00; LEN];
+
+        let _0 = Mpi::new(0).unwrap();
+        let _1 = Mpi::new(1).unwrap();
+        let _2 = Mpi::new(2).unwrap();
+        let n = pk.rsa_public_modulus().unwrap();
+        let nm1 = pk.rsa_public_modulus().unwrap().sub(&Mpi::new(1).unwrap()).unwrap();
+        let nm2 = pk.rsa_public_modulus().unwrap().sub(&Mpi::new(2).unwrap()).unwrap();
+        for c in [_0, _1, nm1, n] {
+            let ct = c.to_binary_padded(LEN).unwrap();
+            let l = pk.decrypt(&ct, &mut pt, rng);
+            assert_eq!(l.unwrap_err(), expected_err);
+        }
+        for c in [_2, nm2] {
+            let ct = c.to_binary_padded(LEN).unwrap();
+            let l = pk.decrypt(&ct, &mut pt, rng);
+            assert_eq!(l.unwrap(), LEN);
+        }
+    }
 }