From 22db646a6d358e08c4c11f12e3dcf96f25525bf8 Mon Sep 17 00:00:00 2001 From: Fam Zheng 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 RH-Acked-by: Kevin Wolf RH-Acked-by: Stefan Hajnoczi 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 Message-id: 1431522721-3266-3-git-send-email-famz@redhat.com Signed-off-by: Stefan Hajnoczi (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 Signed-off-by: Miroslav Rezanina --- 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