From 22db646a6d358e08c4c11f12e3dcf96f25525bf8 Mon Sep 17 00:00:00 2001

From: Fam Zheng <famz@redhat.com>

Date: Mon, 25 May 2015 04:45:56 +0200

Subject: [PATCH 4/6] block: Fix NULL deference for unaligned write if qiov is

 NULL

Message-id: <1432529157-20381-3-git-send-email-famz@redhat.com>

Patchwork-id: 65120

O-Subject: [RHEL-7.2 qemu-kvm PATCH v2 2/3] block: Fix NULL deference for unaligned write if qiov is NULL

Bugzilla: 1200295

RH-Acked-by: Max Reitz <mreitz@redhat.com>

RH-Acked-by: Kevin Wolf <kwolf@redhat.com>

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

For zero write, callers pass in NULL qiov (qemu-io "write -z" or

scsi-disk "write same").

Commit fc3959e466 fixed bdrv_co_write_zeroes which is the common case

for this bug, but it still exists in bdrv_aio_write_zeroes. A simpler

fix would be in bdrv_co_do_pwritev which is the NULL dereference point

and covers both cases.

So don't access it in bdrv_co_do_pwritev in this case, use three aligned

writes.

[Initialize ret to 0 in bdrv_co_do_zero_pwritev() to avoid uninitialized

variable warning with gcc 4.9.2.

--Stefan]

Signed-off-by: Fam Zheng <famz@redhat.com>

Message-id: 1431522721-3266-3-git-send-email-famz@redhat.com

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

(cherry picked from commit 9eeb6dd1b27bd57eb4e3869290e87feac8e8b226)

We don't have block/io.c in downstream, applied the change to

block.c

Signed-off-by: Fam Zheng <famz@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 block.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--

 1 file changed, 95 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c

index 89ab829..45543d5 100644

--- a/block.c

+++ b/block.c

@@ -3069,6 +3069,94 @@ static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,

     return ret;

 }

+static int coroutine_fn bdrv_co_do_zero_pwritev(BlockDriverState *bs,

+                                                int64_t offset,

+                                                unsigned int bytes,

+                                                BdrvRequestFlags flags,

+                                                BdrvTrackedRequest *req)

+{

+    uint8_t *buf = NULL;

+    QEMUIOVector local_qiov;

+    struct iovec iov;

+    uint64_t align = MAX(BDRV_SECTOR_SIZE, bs->request_alignment);

+    unsigned int head_padding_bytes, tail_padding_bytes;

+    int ret = 0;

+

+    head_padding_bytes = offset & (align - 1);

+    tail_padding_bytes = align - ((offset + bytes) & (align - 1));

+

+

+    assert(flags & BDRV_REQ_ZERO_WRITE);

+    if (head_padding_bytes || tail_padding_bytes) {

+        buf = qemu_blockalign(bs, align);

+        iov = (struct iovec) {

+            .iov_base   = buf,

+            .iov_len    = align,

+        };

+        qemu_iovec_init_external(&local_qiov, &iov, 1);

+    }

+    if (head_padding_bytes) {

+        uint64_t zero_bytes = MIN(bytes, align - head_padding_bytes);

+

+        /* RMW the unaligned part before head. */

+        mark_request_serialising(req, align);

+        wait_serialising_requests(req);

+        BLKDBG_EVENT(bs, BLKDBG_PWRITEV_RMW_HEAD);

+        ret = bdrv_aligned_preadv(bs, req, offset & ~(align - 1), align,

+                                  align, &local_qiov, 0);

+        if (ret < 0) {

+            goto fail;

+        }

+        BLKDBG_EVENT(bs, BLKDBG_PWRITEV_RMW_AFTER_HEAD);

+

+        memset(buf + head_padding_bytes, 0, zero_bytes);

+        ret = bdrv_aligned_pwritev(bs, req, offset & ~(align - 1), align,

+                                   &local_qiov,

+                                   flags & ~BDRV_REQ_ZERO_WRITE);

+        if (ret < 0) {

+            goto fail;

+        }

+        offset += zero_bytes;

+        bytes -= zero_bytes;

+    }

+

+    assert(!bytes || (offset & (align - 1)) == 0);

+    if (bytes >= align) {

+        /* Write the aligned part in the middle. */

+        uint64_t aligned_bytes = bytes & ~(align - 1);

+        ret = bdrv_aligned_pwritev(bs, req, offset, aligned_bytes,

+                                   NULL, flags);

+        if (ret < 0) {

+            goto fail;

+        }

+        bytes -= aligned_bytes;

+        offset += aligned_bytes;

+    }

+

+    assert(!bytes || (offset & (align - 1)) == 0);

+    if (bytes) {

+        assert(align == tail_padding_bytes + bytes);

+        /* RMW the unaligned part after tail. */

+        mark_request_serialising(req, align);

+        wait_serialising_requests(req);

+        BLKDBG_EVENT(bs, BLKDBG_PWRITEV_RMW_TAIL);

+        ret = bdrv_aligned_preadv(bs, req, offset, align,

+                                  align, &local_qiov, 0);

+        if (ret < 0) {

+            goto fail;

+        }

+        BLKDBG_EVENT(bs, BLKDBG_PWRITEV_RMW_AFTER_TAIL);

+

+        memset(buf, 0, bytes);

+        ret = bdrv_aligned_pwritev(bs, req, offset, align,

+                                   &local_qiov, flags & ~BDRV_REQ_ZERO_WRITE);

+    }

+fail:

+    qemu_vfree(buf);

+    return ret;

+

+}

+

 /*

  * Handle a write request in coroutine context

  */

@@ -3108,6 +3196,11 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,

      */

     tracked_request_begin(&req, bs, offset, bytes, true);

+    if (!qiov) {

+        ret = bdrv_co_do_zero_pwritev(bs, offset, bytes, flags, &req;;

+        goto out;

+    }

+

     if (offset & (align - 1)) {

         QEMUIOVector head_qiov;

         struct iovec head_iov;

@@ -3181,14 +3274,14 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,

                                flags);

 fail:

-    tracked_request_end(&req;;

     if (use_local_qiov) {

         qemu_iovec_destroy(&local_qiov);

     }

     qemu_vfree(head_buf);

     qemu_vfree(tail_buf);

-

+out:

+    tracked_request_end(&req;;

     return ret;

 }

-- 

1.8.3.1