linux-kernel - [PATCH v4 1/2] lib/mpi: Fix buffer overrun when SG is too long

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Date:   Tue, 27 Dec 2022 10:46:31 +0100
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     dhowells@...hat.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, zohar@...ux.ibm.com,
        dmitry.kasatkin@...il.com, paul@...l-moore.com, jmorris@...ei.org,
        serge@...lyn.com, ebiggers@...nel.org
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...weicloud.com>
Subject: [PATCH v4 1/2] lib/mpi: Fix buffer overrun when SG is too long

From: Herbert Xu <herbert@...dor.apana.org.au>

The helper mpi_read_raw_from_sgl sets the number of entries in
the SG list according to nbytes.  However, if the last entry
in the SG list contains more data than nbytes, then it may overrun
the buffer because it only allocates enough memory for nbytes.

Fixes: 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers")
Reported-by: Roberto Sassu <roberto.sassu@...weicloud.com>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
---
 lib/mpi/mpicoder.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index 39c4c6731094..3cb6bd148fa9 100644
--- a/lib/mpi/mpicoder.c
+++ b/lib/mpi/mpicoder.c
@@ -504,7 +504,8 @@ MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
 
 	while (sg_miter_next(&miter)) {
 		buff = miter.addr;
-		len = miter.length;
+		len = min_t(unsigned, miter.length, nbytes);
+		nbytes -= len;
 
 		for (x = 0; x < len; x++) {
 			a <<= 8;
-- 
2.25.1