[PATCH AUTOSEL 5.4 57/57] s390/archrandom: add parameter check for s390_arch_random_generate

Sasha Levin
2021-05-03T17:00:36Z

From: Harald Freudenberger <freude@linux.ibm.com>

[ Upstream commit 28096067686c5a5cbd4c35b079749bd805df5010 ]

A review of the code showed, that this function which is exposed
within the whole kernel should do a parameter check for the
amount of bytes requested. If this requested bytes is too high
an unsigned int overflow could happen causing this function to
try to memcpy a really big memory chunk.

This is not a security issue as there are only two invocations
of this function from arch/s390/include/asm/archrandom.h and both
are not exposed to userland.

Reported-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/s390/crypto/arch_random.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/arch/s390/crypto/arch_random.c b/arch/s390/crypto/arch_random.c
index dd95cdbd22ce..4cbb4b6d85a8 100644
--- a/arch/s390/crypto/arch_random.c
+++ b/arch/s390/crypto/arch_random.c
@@ -53,6 +53,10 @@ static DECLARE_DELAYED_WORK(arch_rng_work, arch_rng_refill_buffer);

bool s390_arch_random_generate(u8 *buf, unsigned int nbytes)
{
+ /* max hunk is ARCH_RNG_BUF_SIZE */
+ if (nbytes > ARCH_RNG_BUF_SIZE)
+ return false;
+
/* lock rng buffer */
if (!spin_trylock(&arch_rng_lock))
return false;
--
2.30.2