linux-kernel - [PATCH] crypto: mpi: add NULL checks to mpi

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Message-ID: <20240716082825.65219-1-r.smirnov@omp.ru>
Date: Tue, 16 Jul 2024 11:28:25 +0300
From: Roman Smirnov <r.smirnov@....ru>
To: Herbert Xu <herbert@...dor.apana.org.au>, "David S. Miller"
	<davem@...emloft.net>
CC: Roman Smirnov <r.smirnov@....ru>, Mimi Zohar <zohar@...ux.ibm.com>, Sergey
 Shtylyov <s.shtylyov@....ru>, <linux-crypto@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>
Subject: [PATCH] crypto: mpi: add NULL checks to mpi_normalize().

If a->d is NULL, the NULL pointer will be dereferenced. It
is necessary to prevent this case. There is at least one call
stack that can lead to it:

    mpi_ec_curve_point()
      ec_pow2()
        ec_mulm()
          ec_mod()
            mpi_mod()
              mpi_fdiv_r()
                mpi_tdiv_r()
                  mpi_tdiv_qr()
                    mpi_resize()
                      kcalloc()

mpi_resize can return -ENOMEM, but this case is not handled in any way.

Next, dereferencing takes place:

    mpi_ec_curve_point()
      mpi_cmp()
        do_mpi_cmp()
          mpi_normalize()

Found by Linux Verification Center (linuxtesting.org) with Svace.

Signed-off-by: Roman Smirnov <r.smirnov@....ru>
---
 lib/crypto/mpi/mpi-bit.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/crypto/mpi/mpi-bit.c b/lib/crypto/mpi/mpi-bit.c
index 070ba784c9f1..d7420bdb4ff2 100644
--- a/lib/crypto/mpi/mpi-bit.c
+++ b/lib/crypto/mpi/mpi-bit.c
@@ -29,6 +29,9 @@
  */
 void mpi_normalize(MPI a)
 {
+	if (!a || !a->d)
+		return;
+
 	for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--)
 		;
 }
-- 
2.34.1