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a=openpgp; fpr=87A9BD933F87C606D276F62DDAE8E10975969CE5 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 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: 4 X-Spam_score: 0.4 X-Spam_bar: / X-Spam_report: (0.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.811, 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=-0.01, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no 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: 1785828022716158500 The fields last_width and last_height serve two purposes: the text renderer counts in characters, the graphics renderer in pixels. panning_buf reallocation is guarded by geometry-change check, so the unit mismatch can trick it into thinking nothing changed when the resolution actually grew. A guest can trigger this by switching graphics -> text -> graphics: 1. Enter graphics mode with a small width (CR01=3D0x00, 8 pixels). The predicate fires and panning_buf is allocated for that width. 2. Switch to text mode with a large width (CR01=3D0xFF, 256 chars). The text renderer stores 256 into last_width. The text path never touches panning_buf. 3. Switch back to graphics with a width that happens to equal 256 in pixels (CR01=3D0x1F, 32*8 =3D 256). The predicate sees 256 =3D=3D 256 and skips the realloc. With horizontal pel panning enabled, vga_draw_line4() then writes a full 256-pixel scanline into the buffer still sized for 8 pixels -- a 960-byte heap overflow on every scanline, every refresh. Fix it by reallocating unconditionally panning_buf on vga_draw_graphic(). Fixes: CVE-2026-17516 Fixes: 973a724eb006 ("vga: implement horizontal pel panning in graphics mod= es") Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4085 Cc: Paolo Bonzini Signed-off-by: Warisjeet Singh [ Marc- Andr=C3=A9 - drop realloc() resize condition & commit message ] Reviewed-by: Philippe Mathieu-Daud=C3=A9 Signed-off-by: Marc-Andr=C3=A9 Lureau Message-ID: <20260728151456.3704099-1-marcandre.lureau@redhat.com> --- hw/display/vga.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/hw/display/vga.c b/hw/display/vga.c index abe3f8e07758..da0c331486eb 100644 --- a/hw/display/vga.c +++ b/hw/display/vga.c @@ -1647,11 +1647,12 @@ static void vga_draw_graphic(VGACommonState *s, int= full_update) s->last_line_offset =3D s->params.line_offset; s->last_depth =3D depth; s->last_byteswap =3D byteswap; - /* 16 extra pixels are needed for double-width planar modes. */ - s->panning_buf =3D g_realloc(s->panning_buf, - (disp_width + 16) * sizeof(uint32_t)); full_update =3D 1; } + + /* 16 extra pixels are needed for double-width planar modes. */ + s->panning_buf =3D g_realloc(s->panning_buf, + (disp_width + 16) * sizeof(uint32_t)); if (surface_data(surface) !=3D s->vram_ptr + (s->params.start_addr * 4) && !surface_is_allocated(surface)) { /* base address changed (page flip) -> shared display surfaces --=20 2.55.0