crypto: lib/mpi - avoid null pointer deref in mpi_cmp_ui()

During NVMeTCP Authentication a controller can trigger a kernel
oops by specifying the 8192 bit Diffie Hellman group and passing
a correctly sized, but zeroed Diffie Hellamn value.
mpi_cmp_ui() was detecting this if the second parameter was 0,
but 1 is passed from dh_is_pubkey_valid(). This causes the null
pointer u->d to be dereferenced towards the end of mpi_cmp_ui()

Signed-off-by: Mark O'Donovan <shiftee@posteo.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/lib/crypto/mpi/mpi-cmp.c b/lib/crypto/mpi/mpi-cmp.c
index c4cfa3f..0835b62 100644 (file)
--- a/lib/crypto/mpi/mpi-cmp.c
+++ b/lib/crypto/mpi/mpi-cmp.c
@@ -25,8 +25,12 @@ int mpi_cmp_ui(MPI u, unsigned long v)
        mpi_limb_t limb = v;
 
        mpi_normalize(u);
-       if (!u->nlimbs && !limb)
-               return 0;
+       if (u->nlimbs == 0) {
+               if (v == 0)
+                       return 0;
+               else
+                       return -1;
+       }
        if (u->sign)
                return -1;
        if (u->nlimbs > 1)