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a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1784808028; 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=0nIgzkawwNw5P6qL9qW8APCzIW0gYvFSgTcfhT68YqI=; b=FtSRNi2YAcwOzZQTmAqt8LOKDnnt3O38awDnqX4AEvesWbJwjrD7TUMEq85UX9MVV4tFjR lTexTmm/s7e+N5PXkyBsv75f+1uyfhB+WO3/qMEz/sWEHo60S9/mDAsRMWphC3RuvgmEly HIOzbzEBZ8+inTsvNTgAW6fX0CkOjD8= X-MC-Unique: IrFBPXKEMUWWxD048o1aaw-1 X-Mimecast-MFC-AGG-ID: IrFBPXKEMUWWxD048o1aaw_1784808025 From: Thomas Huth To: qemu-devel@nongnu.org, Dmitry Fleytman Cc: qemu-trivial@nongnu.org, qemu-stable@nongnu.org Subject: [PATCH] hw/display/vmware_vga: Don't allow guest to trigger long running loop in host Date: Thu, 23 Jul 2026 14:00:20 +0200 Message-ID: <20260723120020.330089-1-thuth@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists1p.gnu.org; Received-SPF: permerror client-ip=170.10.133.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.951, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, T_SPF_PERMERROR=0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1784808075887158500 Content-Type: text/plain; charset="utf-8" From: Thomas Huth The code in the SVGA_CMD_DEFINE_ALPHA_CURSOR handler in vmsvga_fifo_run() basically does: x =3D vmsvga_fifo_read(s); y =3D vmsvga_fifo_read(s); args =3D x * y; goto badcmd; ... badcmd: len -=3D args; if (len < 0) { goto rewind; } while (args--) { vmsvga_fifo_read(s); } Thus by supplying huge values for x and y that overflow the result of the multiplication, the guest can trigger a long-running loop here that burns the host's CPU cycles. Add some sanity checks so that this cannot happen anymore. Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3782 Reported-by: Feifan Qian Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4026 Reported-by: Tristan Madani Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4076 Reported-by: Sunday Jiang Signed-off-by: Thomas Huth --- hw/display/vmware_vga.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/hw/display/vmware_vga.c b/hw/display/vmware_vga.c index f6f9edfd1d9..04cc438cc02 100644 --- a/hw/display/vmware_vga.c +++ b/hw/display/vmware_vga.c @@ -737,6 +737,9 @@ static void vmsvga_fifo_run(struct vmsvga_state_s *s) vmsvga_fifo_read(s); x =3D vmsvga_fifo_read(s); y =3D vmsvga_fifo_read(s); + if (x < 0 || x >=3D 32768 || y < 0 || y >=3D 32768) { + goto rewind; + } args =3D x * y; goto badcmd; case SVGA_CMD_RECT_ROP_FILL: @@ -776,7 +779,7 @@ static void vmsvga_fifo_run(struct vmsvga_state_s *s) if (len < 0) { goto rewind; } - while (args--) { + while (args-- > 0) { vmsvga_fifo_read(s); } printf("%s: Unknown command 0x%02x in SVGA command FIFO\n", --=20 2.55.0