Currently, mpi_read_buffer() writes full limbs to the output buffer and moves memory around to purge leading zero limbs afterwards. However, with commit 9cbe21d8f89d ("lib/mpi: only require buffers as big as needed for the integer") the caller is only required to provide a buffer large enough to hold the result without the leading zeros. This might result in a buffer overflow for small MP numbers with leading zeros. Fix this by coping the result to its final destination within the output buffer and not copying the leading zeros at all. Fixes: 9cbe21d8f89d ("lib/mpi: only require buffers as big as needed for the integer") Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx> --- lib/mpi/mpicoder.c | 13 +++---------- 1 file changed, 3 insertions(+), 10 deletions(-) diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c index a999ee1..d995a4c 100644 --- a/lib/mpi/mpicoder.c +++ b/lib/mpi/mpicoder.c @@ -201,16 +201,9 @@ int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes, #else #error please implement for this limb size. #endif - memcpy(p, &alimb, BYTES_PER_MPI_LIMB); - p += BYTES_PER_MPI_LIMB; - if (lzeros > 0) { - mpi_limb_t *limb1 = (void *)p - sizeof(alimb); - mpi_limb_t *limb2 = (void *)p - sizeof(alimb) - + lzeros; - *limb1 = *limb2; - p -= lzeros; - lzeros -= sizeof(alimb); - } + memcpy(p, (u8 *)&alimb + lzeros, BYTES_PER_MPI_LIMB - lzeros); + p += BYTES_PER_MPI_LIMB - lzeros; + lzeros = 0; } return 0; } -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html