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a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1741603747; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=I36Dcvi268C2V8W9mc+7VsefR7nGxhlXfzQDjKPhpfE=; b=Li04kZXkOiLbTYJZdQ7zVhNxKdCvltzl8g373JRH8wTnhgK9FOqAyWKZY7ANMZAIcIIaEu P4HvjRa7GsTkeOrxYFI9z8nbSW+lIgsSwadFD9AQBW9huKJj7cLbqAUnSo/Y6JDE0lJldC Idc0VbiaIIFZ2lUaxxVWPo6BXMV+S7o= X-MC-Unique: UyEXadnENGW9rt4aAi1DbQ-1 X-Mimecast-MFC-AGG-ID: UyEXadnENGW9rt4aAi1DbQ_1741603743 From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, gerben@altlinux.org, qemu-stable@nongnu.org, qemu-devel@nongnu.org Subject: [PATCH] block: Zero block driver state before reopening Date: Mon, 10 Mar 2025 11:48:58 +0100 Message-ID: <20250310104858.28221-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" Block drivers assume in their .bdrv_open() implementation that their state in bs->opaque has been zeroed; it is initially allocated with g_malloc0() in bdrv_open_driver(). bdrv_snapshot_goto() needs to make sure that it is zeroed again before calling drv->bdrv_open() to avoid that block drivers use stale values. One symptom of this bug is VMDK running into a double free when the user tries to apply an internal snapshot like 'qemu-img snapshot -a test test.vmdk'. This should be a graceful error because VMDK doesn't support internal snapshots. =3D=3D25507=3D=3D Invalid free() / delete / delete[] / realloc() =3D=3D25507=3D=3D at 0x484B347: realloc (vg_replace_malloc.c:1801) =3D=3D25507=3D=3D by 0x54B592A: g_realloc (gmem.c:171) =3D=3D25507=3D=3D by 0x1B221D: vmdk_add_extent (../block/vmdk.c:570) =3D=3D25507=3D=3D by 0x1B1084: vmdk_open_sparse (../block/vmdk.c:1059) =3D=3D25507=3D=3D by 0x1AF3D8: vmdk_open (../block/vmdk.c:1371) =3D=3D25507=3D=3D by 0x1A2AE0: bdrv_snapshot_goto (../block/snapshot.c:2= 99) =3D=3D25507=3D=3D by 0x205C77: img_snapshot (../qemu-img.c:3500) =3D=3D25507=3D=3D by 0x58FA087: (below main) (libc_start_call_main.h:58) =3D=3D25507=3D=3D Address 0x832f3e0 is 0 bytes inside a block of size 272 = free'd =3D=3D25507=3D=3D at 0x4846B83: free (vg_replace_malloc.c:989) =3D=3D25507=3D=3D by 0x54AEAC4: g_free (gmem.c:208) =3D=3D25507=3D=3D by 0x1AF629: vmdk_close (../block/vmdk.c:2889) =3D=3D25507=3D=3D by 0x1A2A9C: bdrv_snapshot_goto (../block/snapshot.c:2= 90) =3D=3D25507=3D=3D by 0x205C77: img_snapshot (../qemu-img.c:3500) =3D=3D25507=3D=3D by 0x58FA087: (below main) (libc_start_call_main.h:58) This error was discovered by fuzzing qemu-img. Cc: qemu-stable@nongnu.org Reported-by: Denis Rastyogin Signed-off-by: Kevin Wolf Reviewed-by: Eric Blake --- block/snapshot.c | 1 + 1 file changed, 1 insertion(+) diff --git a/block/snapshot.c b/block/snapshot.c index 9c44780e96..22567f1fb9 100644 --- a/block/snapshot.c +++ b/block/snapshot.c @@ -296,6 +296,7 @@ int bdrv_snapshot_goto(BlockDriverState *bs, bdrv_graph_wrunlock(); =20 ret =3D bdrv_snapshot_goto(fallback_bs, snapshot_id, errp); + memset(bs->opaque, 0, drv->instance_size); open_ret =3D drv->bdrv_open(bs, options, bs->open_flags, &local_er= r); qobject_unref(options); if (open_ret < 0) { --=20 2.48.1