[PATCH] lib/mpi: Fix buffer overrun when SG is too long

Herbert Xu
2022-12-20T07:25:47Z

On Mon, Dec 19, 2022 at 09:49:29AM +0100, Roberto Sassu wrote:
>
> do you have any news on this bug?

Thanks for the reminder. Could you please try this patch?

---8<---
The helper mpi_read_raw_from_sgl ignores the second parameter
nbytes when reading the SG list and may overrun its own buffer
because it only allocates enough memory according to nbytes.

Fixes: 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers")
Reported-by: Roberto Sassu <roberto.sassu@huaweicloud.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index 39c4c6731094..6bffc68c1a5a 100644
--- a/lib/mpi/mpicoder.c
+++ b/lib/mpi/mpicoder.c
@@ -494,17 +494,15 @@ MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
val->sign = 0;
val->nlimbs = nlimbs;

- if (nbytes == 0)
- return val;
-
j = nlimbs - 1;
a = 0;
z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
z %= BYTES_PER_MPI_LIMB;

- while (sg_miter_next(&miter)) {
+ while (nbytes && 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;
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt