lib/mpi: Fix karactx leak in mpi_powm

commit c8ea9fce2baf7b643384f36f29e4194fa40d33a6 upstream.

Sometimes mpi_powm will leak karactx because a memory allocation
failure causes a bail-out that skips the freeing of karactx.  This
patch moves the freeing of karactx to the end of the function like
everything else so that it can't be skipped.

Reported-by: syzbot+f7baccc38dcc1e094e77@syzkaller.appspotmail.com
Fixes: cdec9cb5167a ("crypto: GnuPG based MPI lib - source files...")
Cc: <stable@vger.kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c
index 468fb7cd1221ef77240dac361c4e967268b9318e..edf345b7f06b6fed6769872038a25a5487cee462 100644 (file)
--- a/lib/mpi/mpi-pow.c
+++ b/lib/mpi/mpi-pow.c
@@ -37,6 +37,7 @@
 int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
 {
        mpi_ptr_t mp_marker = NULL, bp_marker = NULL, ep_marker = NULL;
+       struct karatsuba_ctx karactx = {};
        mpi_ptr_t xp_marker = NULL;
        mpi_ptr_t tspace = NULL;
        mpi_ptr_t rp, ep, mp, bp;
@@ -164,13 +165,11 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
                int c;
                mpi_limb_t e;
                mpi_limb_t carry_limb;
-               struct karatsuba_ctx karactx;
 
                xp = xp_marker = mpi_alloc_limb_space(2 * (msize + 1));
                if (!xp)
                        goto enomem;
 
-               memset(&karactx, 0, sizeof karactx);
                negative_result = (ep[0] & 1) && base->sign;
 
                i = esize - 1;
@@ -295,8 +294,6 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
                if (mod_shift_cnt)
                        mpihelp_rshift(rp, rp, rsize, mod_shift_cnt);
                MPN_NORMALIZE(rp, rsize);
-
-               mpihelp_release_karatsuba_ctx(&karactx);
        }
 
        if (negative_result && rsize) {
@@ -313,6 +310,7 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
 leave:
        rc = 0;
 enomem:
+       mpihelp_release_karatsuba_ctx(&karactx);
        if (assign_rp)
                mpi_assign_limb_space(res, rp, size);
        if (mp_marker)