[PATCH 6.1 092/195] dm-verity: recheck the hash after a failure

Greg Kroah-Hartman
2024-02-27T14:16:35Z

From: Mikulas Patocka <mpatocka@redhat.com>

commit 9177f3c0dea6143d05cac1bbd28668fd0e216d11 upstream.

If a userspace process reads (with O_DIRECT) multiple blocks into the same
buffer, dm-verity reports an error [1].

This commit fixes dm-verity, so that if hash verification fails, the data
is read again into a kernel buffer (where userspace can't modify it) and
the hash is rechecked. If the recheck succeeds, the content of the kernel
buffer is copied into the user buffer; if the recheck fails, an error is
reported.

[1] https://people.redhat.com/~mpatocka/testcases/blk-auth-modify/read2.c

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/dm-verity-target.c | 86 +++++++++++++++++++++++++++++++++++++++---
drivers/md/dm-verity.h | 6 ++
2 files changed, 86 insertions(+), 6 deletions(-)

--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -474,6 +474,63 @@ int verity_for_bv_block(struct dm_verity
return 0;
}

+static int verity_recheck_copy(struct dm_verity *v, struct dm_verity_io *io,
+ u8 *data, size_t len)
+{
+ memcpy(data, io->recheck_buffer, len);
+ io->recheck_buffer += len;
+
+ return 0;
+}
+
+static int verity_recheck(struct dm_verity *v, struct dm_verity_io *io,
+ struct bvec_iter start, sector_t cur_block)
+{
+ struct page *page;
+ void *buffer;
+ int r;
+ struct dm_io_request io_req;
+ struct dm_io_region io_loc;
+
+ page = mempool_alloc(&v->recheck_pool, GFP_NOIO);
+ buffer = page_to_virt(page);
+
+ io_req.bi_opf = REQ_OP_READ;
+ io_req.mem.type = DM_IO_KMEM;
+ io_req.mem.ptr.addr = buffer;
+ io_req.notify.fn = NULL;
+ io_req.client = v->io;
+ io_loc.bdev = v->data_dev->bdev;
+ io_loc.sector = cur_block << (v->data_dev_block_bits - SECTOR_SHIFT);
+ io_loc.count = 1 << (v->data_dev_block_bits - SECTOR_SHIFT);
+ r = dm_io(&io_req, 1, &io_loc, NULL);
+ if (unlikely(r))
+ goto free_ret;
+
+ r = verity_hash(v, verity_io_hash_req(v, io), buffer,
+ 1 << v->data_dev_block_bits,
+ verity_io_real_digest(v, io), true);
+ if (unlikely(r))
+ goto free_ret;
+
+ if (memcmp(verity_io_real_digest(v, io),
+ verity_io_want_digest(v, io), v->digest_size)) {
+ r = -EIO;
+ goto free_ret;
+ }
+
+ io->recheck_buffer = buffer;
+ r = verity_for_bv_block(v, io, &start, verity_recheck_copy);
+ if (unlikely(r))
+ goto free_ret;
+
+ r = 0;
+free_ret:
+ mempool_free(page, &v->recheck_pool);
+
+ return r;
+}
+
static int verity_bv_zero(struct dm_verity *v, struct dm_verity_io *io,
u8 *data, size_t len)
{
@@ -500,9 +557,7 @@ static int verity_verify_io(struct dm_ve
{
bool is_zero;
struct dm_verity *v = io->v;
-#if defined(CONFIG_DM_VERITY_FEC)
struct bvec_iter start;
-#endif
struct bvec_iter iter_copy;
struct bvec_iter *iter;
struct crypto_wait wait;
@@ -553,10 +608,7 @@ static int verity_verify_io(struct dm_ve
if (unlikely(r < 0))
return r;

-#if defined(CONFIG_DM_VERITY_FEC)
- if (verity_fec_is_enabled(v))
- start = *iter;
-#endif
+ start = *iter;
r = verity_for_io_block(v, io, iter, &wait);
if (unlikely(r < 0))
return r;
@@ -578,6 +630,10 @@ static int verity_verify_io(struct dm_ve
* tasklet since it may sleep, so fallback to work-queue.
*/
return -EAGAIN;
+ } else if (verity_recheck(v, io, start, cur_block) == 0) {
+ if (v->validated_blocks)
+ set_bit(cur_block, v->validated_blocks);
+ continue;
#if defined(CONFIG_DM_VERITY_FEC)
} else if (verity_fec_decode(v, io, DM_VERITY_BLOCK_TYPE_DATA,
cur_block, NULL, &start) == 0) {
@@ -928,6 +984,10 @@ static void verity_dtr(struct dm_target
if (v->verify_wq)
destroy_workqueue(v->verify_wq);

+ mempool_exit(&v->recheck_pool);
+ if (v->io)
+ dm_io_client_destroy(v->io);
+
if (v->bufio)
dm_bufio_client_destroy(v->bufio);

@@ -1364,6 +1424,20 @@ static int verity_ctr(struct dm_target *
}
v->hash_blocks = hash_position;

+ r = mempool_init_page_pool(&v->recheck_pool, 1, 0);
+ if (unlikely(r)) {
+ ti->error = "Cannot allocate mempool";
+ goto bad;
+ }
+
+ v->io = dm_io_client_create();
+ if (IS_ERR(v->io)) {
+ r = PTR_ERR(v->io);
+ v->io = NULL;
+ ti->error = "Cannot allocate dm io";
+ goto bad;
+ }
+
v->bufio = dm_bufio_client_create(v->hash_dev->bdev,
1 << v->hash_dev_block_bits, 1, sizeof(struct buffer_aux),
dm_bufio_alloc_callback, NULL,
--- a/drivers/md/dm-verity.h
+++ b/drivers/md/dm-verity.h
@@ -11,6 +11,7 @@
#ifndef DM_VERITY_H
#define DM_VERITY_H

+#include <linux/dm-io.h>
#include <linux/dm-bufio.h>
#include <linux/device-mapper.h>
#include <linux/interrupt.h>
@@ -68,6 +69,9 @@ struct dm_verity {
unsigned long *validated_blocks; /* bitset blocks validated */

char *signature_key_desc; /* signature keyring reference */
+
+ struct dm_io_client *io;
+ mempool_t recheck_pool;
};

struct dm_verity_io {
@@ -84,6 +88,8 @@ struct dm_verity_io {

struct work_struct work;

+ char *recheck_buffer;
+
/*
* Three variably-size fields follow this struct:
*