mpi: Improve gcry_mpi_invm to detect bad input.

* mpi/mpi-inv.c (gcry_mpi_invm): Return 0 for bad input.
--

Without this patch the function may enter and endless loop.

Signed-off-by: Werner Koch <wk@gnupg.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/mpi/mpi-inv.c b/mpi/mpi-inv.c
index 5d269466..15fa58ff 100644
--- a/mpi/mpi-inv.c
+++ b/mpi/mpi-inv.c
@@ -165,6 +165,11 @@ gcry_mpi_invm( gcry_mpi_t x, gcry_mpi_t a, gcry_mpi_t n )
     int sign;
     int odd ;
 
+    if (!mpi_cmp_ui (a, 0))
+        return 0; /* Inverse does not exists.  */
+    if (!mpi_cmp_ui (n, 1))
+        return 0; /* Inverse does not exists.  */
+
     u = mpi_copy(a);
     v = mpi_copy(n);