linux-kernel - [PATCH AUTOSEL 5.15 07/15] crypto: lib/mpi - avoid null pointer deref in mpi_cmp

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Message-Id: <20230908181920.3460520-7-sashal@kernel.org>
Date:   Fri,  8 Sep 2023 14:19:10 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Mark O'Donovan <shiftee@...teo.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Sasha Levin <sashal@...nel.org>, zohar@...ux.ibm.com
Subject: [PATCH AUTOSEL 5.15 07/15] crypto: lib/mpi - avoid null pointer deref in mpi_cmp_ui()

From: Mark O'Donovan <shiftee@...teo.net>

[ Upstream commit 9e47a758b70167c9301d2b44d2569f86c7796f2d ]

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@...teo.net>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 lib/mpi/mpi-cmp.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/mpi/mpi-cmp.c b/lib/mpi/mpi-cmp.c
index c4cfa3ff05818..0835b6213235e 100644
--- a/lib/mpi/mpi-cmp.c
+++ b/lib/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)
-- 
2.40.1