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Mon, 09 Mar 2026 12:01:57 -0700 (PDT) X-Received: by 2002:a05:600c:8488:b0:485:3989:b3e4 with SMTP id 5b1f17b1804b1-485419b61a2mr10820735e9.6.1773082917435; Mon, 09 Mar 2026 12:01:57 -0700 (PDT) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: mcascell@redhat.com, security@1seal.org, =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Subject: [PATCH] hyperv/syndbg: check length returned by cpu_physical_memory_map() [Fixes: CVE-2026-3842] Date: Mon, 9 Mar 2026 20:01:44 +0100 Message-ID: <20260309190155.80619-1-pbonzini@redhat.com> X-Mailer: git-send-email 2.53.0 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable 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=lists.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -3 X-Spam_score: -0.4 X-Spam_bar: / X-Spam_report: (-0.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.819, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.903, 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: 1773082944204154100 If cpu_physical_memory_map() returns a length shorter than the one that was passed into the function, writing the full out_len bytes causes an access beyond the memory allocated to the guest; or in the case of the MMIO bounce buffer, an out-of-bounds access in a heap-allocated object. Add a check similar to the one already in handle_send_msg(), and take the occasion to remove repeated computations of recv_byte_count + UDP_PKT_HEADER_SIZE and clarify that the code does not write past out_len bytes. Reported-by: Oleh Konko Reviewed-by: Daniel P. Berrang=C3=A9 Signed-off-by: Paolo Bonzini --- hw/hyperv/syndbg.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-) diff --git a/hw/hyperv/syndbg.c b/hw/hyperv/syndbg.c index 1e177f9dd82..10171b19e8f 100644 --- a/hw/hyperv/syndbg.c +++ b/hw/hyperv/syndbg.c @@ -194,7 +194,7 @@ static uint16_t handle_recv_msg(HvSynDbg *syndbg, uint6= 4_t outgpa, uint16_t ret; g_assert(MSG_BUFSZ >=3D qemu_target_page_size()); QEMU_UNINITIALIZED uint8_t data_buf[MSG_BUFSZ]; - hwaddr out_len; + hwaddr out_len, out_requested_len; void *out_data; ssize_t recv_byte_count; =20 @@ -223,29 +223,28 @@ static uint16_t handle_recv_msg(HvSynDbg *syndbg, uin= t64_t outgpa, if (is_raw) { out_len +=3D UDP_PKT_HEADER_SIZE; } + out_requested_len =3D out_len; out_data =3D cpu_physical_memory_map(outgpa, &out_len, 1); - if (!out_data) { - return HV_STATUS_INSUFFICIENT_MEMORY; + ret =3D HV_STATUS_INSUFFICIENT_MEMORY; + if (!out_data || out_len < out_requested_len) { + goto cleanup_out_data; } =20 if (is_raw && - !create_udp_pkt(syndbg, out_data, - recv_byte_count + UDP_PKT_HEADER_SIZE, + !create_udp_pkt(syndbg, out_data, out_len, data_buf, recv_byte_count)) { - ret =3D HV_STATUS_INSUFFICIENT_MEMORY; goto cleanup_out_data; } else if (!is_raw) { - memcpy(out_data, data_buf, recv_byte_count); + memcpy(out_data, data_buf, out_len); } =20 - *retrieved_count =3D recv_byte_count; - if (is_raw) { - *retrieved_count +=3D UDP_PKT_HEADER_SIZE; - } + *retrieved_count =3D out_len; ret =3D HV_STATUS_SUCCESS; =20 cleanup_out_data: - cpu_physical_memory_unmap(out_data, out_len, 1, out_len); + if (out_data) { + cpu_physical_memory_unmap(out_data, out_len, 1, out_len); + } return ret; } =20 --=20 2.53.0