[PATCH 4.9 16/25] crypto: dh - Fix double free of ctx->p

Greg Kroah-Hartman
2017-11-22T10:14:28Z

From: Eric Biggers <ebiggers@google.com>

commit 12d41a023efb01b846457ccdbbcbe2b65a87d530 upstream.

When setting the secret with the software Diffie-Hellman implementation,
if allocating 'g' failed (e.g. if it was longer than
MAX_EXTERN_MPI_BITS), then 'p' was freed twice: once immediately, and
once later when the crypto_kpp tfm was destroyed.

Fix it by using dh_free_ctx() (renamed to dh_clear_ctx()) in the error
paths, as that correctly sets the pointers to NULL.

KASAN report:

MPI: mpi too large (32760 bits)
==================================================================
BUG: KASAN: use-after-free in mpi_free+0x131/0x170
Read of size 4 at addr ffff88006c7cdf90 by task reproduce_doubl/367

CPU: 1 PID: 367 Comm: reproduce_doubl Not tainted 4.14.0-rc7-00040-g05298abde6fe #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
dump_stack+0xb3/0x10b
? mpi_free+0x131/0x170
print_address_description+0x79/0x2a0
? mpi_free+0x131/0x170
kasan_report+0x236/0x340
? akcipher_register_instance+0x90/0x90
__asan_report_load4_noabort+0x14/0x20
mpi_free+0x131/0x170
? akcipher_register_instance+0x90/0x90
dh_exit_tfm+0x3d/0x140
crypto_kpp_exit_tfm+0x52/0x70
crypto_destroy_tfm+0xb3/0x250
__keyctl_dh_compute+0x640/0xe90
? kasan_slab_free+0x12f/0x180
? dh_data_from_key+0x240/0x240
? key_create_or_update+0x1ee/0xb20
? key_instantiate_and_link+0x440/0x440
? lock_contended+0xee0/0xee0
? kfree+0xcf/0x210
? SyS_add_key+0x268/0x340
keyctl_dh_compute+0xb3/0xf1
? __keyctl_dh_compute+0xe90/0xe90
? SyS_add_key+0x26d/0x340
? entry_SYSCALL_64_fastpath+0x5/0xbe
? trace_hardirqs_on_caller+0x3f4/0x560
SyS_keyctl+0x72/0x2c0
entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x43ccf9
RSP: 002b:00007ffeeec96158 EFLAGS: 00000246 ORIG_RAX: 00000000000000fa
RAX: ffffffffffffffda RBX: 000000000248b9b9 RCX: 000000000043ccf9
RDX: 00007ffeeec96170 RSI: 00007ffeeec96160 RDI: 0000000000000017
RBP: 0000000000000046 R08: 0000000000000000 R09: 0248b9b9143dc936
R10: 0000000000001000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000409670 R14: 0000000000409700 R15: 0000000000000000

Allocated by task 367:
save_stack_trace+0x16/0x20
kasan_kmalloc+0xeb/0x180
kmem_cache_alloc_trace+0x114/0x300
mpi_alloc+0x4b/0x230
mpi_read_raw_data+0xbe/0x360
dh_set_secret+0x1dc/0x460
__keyctl_dh_compute+0x623/0xe90
keyctl_dh_compute+0xb3/0xf1
SyS_keyctl+0x72/0x2c0
entry_SYSCALL_64_fastpath+0x1f/0xbe

Freed by task 367:
save_stack_trace+0x16/0x20
kasan_slab_free+0xab/0x180
kfree+0xb5/0x210
mpi_free+0xcb/0x170
dh_set_secret+0x2d7/0x460
__keyctl_dh_compute+0x623/0xe90
keyctl_dh_compute+0xb3/0xf1
SyS_keyctl+0x72/0x2c0
entry_SYSCALL_64_fastpath+0x1f/0xbe

Fixes: 802c7f1c84e4 ("crypto: dh - Add DH software implementation")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
crypto/dh.c | 33 +++++++++++++--------------------
1 file changed, 13 insertions(+), 20 deletions(-)

--- a/crypto/dh.c
+++ b/crypto/dh.c
@@ -21,19 +21,12 @@ struct dh_ctx {
MPI xa;
};

-static inline void dh_clear_params(struct dh_ctx *ctx)
+static void dh_clear_ctx(struct dh_ctx *ctx)
{
mpi_free(ctx->p);
mpi_free(ctx->g);
- ctx->p = NULL;
- ctx->g = NULL;
-}
-
-static void dh_free_ctx(struct dh_ctx *ctx)
-{
- dh_clear_params(ctx);
mpi_free(ctx->xa);
- ctx->xa = NULL;
+ memset(ctx, 0, sizeof(*ctx));
}

/*
@@ -71,10 +64,8 @@ static int dh_set_params(struct dh_ctx *
return -EINVAL;

ctx->g = mpi_read_raw_data(params->g, params->g_size);
- if (!ctx->g) {
- mpi_free(ctx->p);
+ if (!ctx->g)
return -EINVAL;
- }

return 0;
}
@@ -85,21 +76,23 @@ static int dh_set_secret(struct crypto_k
struct dh params;

/* Free the old MPI key if any */
- dh_free_ctx(ctx);
+ dh_clear_ctx(ctx);

if (crypto_dh_decode_key(buf, len, &params) < 0)
- return -EINVAL;
+ goto err_clear_ctx;

if (dh_set_params(ctx, &params) < 0)
- return -EINVAL;
+ goto err_clear_ctx;

ctx->xa = mpi_read_raw_data(params.key, params.key_size);
- if (!ctx->xa) {
- dh_clear_params(ctx);
- return -EINVAL;
- }
+ if (!ctx->xa)
+ goto err_clear_ctx;

return 0;
+
+err_clear_ctx:
+ dh_clear_ctx(ctx);
+ return -EINVAL;
}

static int dh_compute_value(struct kpp_request *req)
@@ -157,7 +150,7 @@ static void dh_exit_tfm(struct crypto_kp
{
struct dh_ctx *ctx = dh_get_ctx(tfm);

- dh_free_ctx(ctx);
+ dh_clear_ctx(ctx);
}

static struct kpp_alg dh = {