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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1783691368; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=EhTR2MjQSarOvx0KROWJm40uQobi38h8qa+ZZ9zIx+U=; b=cYlYF6k4JhboBwZytVE3uPHGuBXwcsJrzSyw7Z9qgwo4GJ6VgWJNxx/257KPi5RP8Ya7Yi 2THquamTI7aMg3rFPz1NMMisFKLh3WHbeeOnZfaT54NJkqZMODbwqzgyjW0ElQ3B1Hv+s1 GxVw/5rN4QxMOEf4lY58ITCx7otfZ6w= X-MC-Unique: 6-oXu1LlM3aprnXWt-4gjw-1 X-Mimecast-MFC-AGG-ID: 6-oXu1LlM3aprnXWt-4gjw_1783691366 From: marcandre.lureau@redhat.com To: qemu-devel@nongnu.org Cc: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= Subject: [PATCH] ui/vnc: fix out-of-bounds write in lossy refresh dirty marking Date: Fri, 10 Jul 2026 17:49:21 +0400 Message-ID: <20260710134921.2321027-1-marcandre.lureau@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" 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: pass client-ip=170.10.133.124; envelope-from=marcandre.lureau@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 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: 1783691391137158500 From: Marc-Andr=C3=A9 Lureau vnc_refresh_lossy_rect() marks a full VNC_STAT_RECT (64) rows of the dirty bitmap when refreshing a lossy tile. When the display height is not a multiple of VNC_STAT_RECT, the last tile row is a partial tile and the loop writes past the end of vs->dirty[VNC_MAX_HEIGHT]. For example, with a 2160-pixel-high display (VNC_MAX_HEIGHT), the last stat tile starts at y=3D2112. The unconditional 64-row loop writes rows 2112..2175, overflowing 16 rows (640 bytes) past the dirty bitmap into subsequent VncState fields. Fix by passing the effective display height into vnc_refresh_lossy_rect() and clamping the inner loop. Fixes: CVE-2026-61475 Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3935 Reported-by: "Vulnerability Report" Signed-off-by: Marc-Andre Lureau --- ui/vnc.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/ui/vnc.c b/ui/vnc.c index b2b69923b75..dfc8262d42a 100644 --- a/ui/vnc.c +++ b/ui/vnc.c @@ -2998,15 +2998,18 @@ void vnc_sent_lossy_rect(VncWorker *worker, int x, = int y, int w, int h) } } =20 -static int vnc_refresh_lossy_rect(VncDisplay *vd, int x, int y) +static int vnc_refresh_lossy_rect(VncDisplay *vd, int x, int y, + int height) { VncState *vs; int sty =3D y / VNC_STAT_RECT; int stx =3D x / VNC_STAT_RECT; int has_dirty =3D 0; + int rows; =20 y =3D QEMU_ALIGN_DOWN(y, VNC_STAT_RECT); x =3D QEMU_ALIGN_DOWN(x, VNC_STAT_RECT); + rows =3D MIN(VNC_STAT_RECT, height - y); =20 QTAILQ_FOREACH(vs, &vd->clients, next) { VncConnection *vc =3D container_of(vs, VncConnection, vs); @@ -3022,7 +3025,7 @@ static int vnc_refresh_lossy_rect(VncDisplay *vd, int= x, int y) } =20 vc->worker.lossy_rect[sty][stx] =3D 0; - for (j =3D 0; j < VNC_STAT_RECT; ++j) { + for (j =3D 0; j < rows; ++j) { bitmap_set(vs->dirty[y + j], x / VNC_DIRTY_PIXELS_PER_BIT, VNC_STAT_RECT / VNC_DIRTY_PIXELS_PER_BIT); @@ -3073,7 +3076,7 @@ static int vnc_update_stats(VncDisplay *vd, struct t= imeval * tv) =20 if (timercmp(&res, &VNC_REFRESH_LOSSY, >)) { rect->freq =3D 0; - has_dirty +=3D vnc_refresh_lossy_rect(vd, x, y); + has_dirty +=3D vnc_refresh_lossy_rect(vd, x, y, height); memset(rect->times, 0, sizeof (rect->times)); continue ; } --=20 2.55.0