From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 845D219A288; Fri, 24 Apr 2026 13:42:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777038148; cv=none; b=a2WNw4RoAPR0w5MwDkfg2P0Sw/DracUp2d2GRoxViU89hE95TfxYUFJ0Yv9O8DUojdRRqdm/8ffrDwtN6Tz8FvZuej8BzrgKg/C6vZzJxBcOlXwxHs+9t2aGn+noNHT81MsDXEle3GDn4FWQuGqp6WKDWW5IAI4S2jBdHWdFUek= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777038148; c=relaxed/simple; bh=5bJHZJnHyWgb7lXnm1bacvbiENsykU/2QR0z9WxYvUM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=psIs2dQhn+XguAtFkoVdgD+erS3yQ+YoQTgkB4VeThliiJZ6MQc3m8gYDzY69O509AgoS6rKL16Lm9SqZqe+AgSoabUYKflD87J9/kuUUX9f7TLe5VrkOqcEEy99rUIJSUS59sZAi0O2VpYZWDa81iS6IAPQp11li6EPs0KBihM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=h7xbsiOq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="h7xbsiOq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 10BE6C19425; Fri, 24 Apr 2026 13:42:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1777038148; bh=5bJHZJnHyWgb7lXnm1bacvbiENsykU/2QR0z9WxYvUM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=h7xbsiOqEbpvXfjLmyXirrjyVIKy9kRe5ESyMm1ydWH6He64okbbF2mBa7+LY9c2B gZKwSwxVDXVoquMTqrfWSsHQ8z0FXIg3vOGaEMmmPjiuyzeSmU/3jVmYkiRjn3bVVV dH+KtPpRXsoDWwfeoij8SPKjv5ZmFS7Qe1d5cGRU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Michael Bommarito , Namjae Jeon , Steve French Subject: [PATCH 6.18 42/55] ksmbd: validate num_aces and harden ACE walk in smb_inherit_dacl() Date: Fri, 24 Apr 2026 15:31:21 +0200 Message-ID: <20260424132438.766214932@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260424132430.006424517@linuxfoundation.org> References: <20260424132430.006424517@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michael Bommarito commit 3e4e2ea2a781018ed5d75f969e3e5606beb66e48 upstream. smb_inherit_dacl() trusts the on-disk num_aces value from the parent directory's DACL xattr and uses it to size a heap allocation: aces_base = kmalloc(sizeof(struct smb_ace) * num_aces * 2, ...); num_aces is a u16 read from le16_to_cpu(parent_pdacl->num_aces) without checking that it is consistent with the declared pdacl_size. An authenticated client whose parent directory's security.NTACL is tampered (e.g. via offline xattr corruption or a concurrent path that bypasses parse_dacl()) can present num_aces = 65535 with minimal actual ACE data. This causes a ~8 MB allocation (not kzalloc, so uninitialized) that the subsequent loop only partially populates, and may also overflow the three-way size_t multiply on 32-bit kernels. Additionally, the ACE walk loop uses the weaker offsetof(struct smb_ace, access_req) minimum size check rather than the minimum valid on-wire ACE size, and does not reject ACEs whose declared size is below the minimum. Reproduced on UML + KASAN + LOCKDEP against the real ksmbd code path. A legitimate mount.cifs client creates a parent directory over SMB (ksmbd writes a valid security.NTACL xattr), then the NTACL blob on the backing filesystem is rewritten to set num_aces = 0xFFFF while keeping the posix_acl_hash bytes intact so ksmbd_vfs_get_sd_xattr()'s hash check still passes. A subsequent SMB2 CREATE of a child under that parent drives smb2_open() into smb_inherit_dacl() (share has "vfs objects = acl_xattr" set), which fails the page allocator: WARNING: mm/page_alloc.c:5226 at __alloc_frozen_pages_noprof+0x46c/0x9c0 Workqueue: ksmbd-io handle_ksmbd_work __alloc_frozen_pages_noprof+0x46c/0x9c0 ___kmalloc_large_node+0x68/0x130 __kmalloc_large_node_noprof+0x24/0x70 __kmalloc_noprof+0x4c9/0x690 smb_inherit_dacl+0x394/0x2430 smb2_open+0x595d/0xabe0 handle_ksmbd_work+0x3d3/0x1140 With the patch applied the added guard rejects the tampered value with -EINVAL before any large allocation runs, smb2_open() falls back to smb2_create_sd_buffer(), and the child is created with a default SD. No warning, no splat. Fix by: 1. Validating num_aces against pdacl_size using the same formula applied in parse_dacl(). 2. Replacing the raw kmalloc(sizeof * num_aces * 2) with kmalloc_array(num_aces * 2, sizeof(...)) for overflow-safe allocation. 3. Tightening the per-ACE loop guard to require the minimum valid ACE size (offsetof(smb_ace, sid) + CIFS_SID_BASE_SIZE) and rejecting under-sized ACEs, matching the hardening in smb_check_perm_dacl() and parse_dacl(). v1 -> v2: - Replace the synthetic test-module splat in the changelog with a real-path UML + KASAN reproduction driven through mount.cifs and SMB2 CREATE; Namjae flagged the kcifs3_test_inherit_dacl_old name in v1 since it does not exist in ksmbd. - Drop the commit-hash citation from the code comment per Namjae's review; keep the parse_dacl() pointer. Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Michael Bommarito Acked-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman --- fs/smb/server/smbacl.c | 28 +++++++++++++++++++++++----- 1 file changed, 23 insertions(+), 5 deletions(-) --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -1106,8 +1106,24 @@ int smb_inherit_dacl(struct ksmbd_conn * goto free_parent_pntsd; } - aces_base = kmalloc(sizeof(struct smb_ace) * num_aces * 2, - KSMBD_DEFAULT_GFP); + aces_size = pdacl_size - sizeof(struct smb_acl); + + /* + * Validate num_aces against the DACL payload before allocating. + * Each ACE must be at least as large as its fixed-size header + * (up to the SID base), so num_aces cannot exceed the payload + * divided by the minimum ACE size. This mirrors the existing + * check in parse_dacl(). + */ + if (num_aces > aces_size / (offsetof(struct smb_ace, sid) + + offsetof(struct smb_sid, sub_auth) + + sizeof(__le16))) { + rc = -EINVAL; + goto free_parent_pntsd; + } + + aces_base = kmalloc_array(num_aces * 2, sizeof(struct smb_ace), + KSMBD_DEFAULT_GFP); if (!aces_base) { rc = -ENOMEM; goto free_parent_pntsd; @@ -1116,7 +1132,6 @@ int smb_inherit_dacl(struct ksmbd_conn * aces = (struct smb_ace *)aces_base; parent_aces = (struct smb_ace *)((char *)parent_pdacl + sizeof(struct smb_acl)); - aces_size = acl_len - sizeof(struct smb_acl); if (pntsd_type & DACL_AUTO_INHERITED) inherited_flags = INHERITED_ACE; @@ -1124,11 +1139,14 @@ int smb_inherit_dacl(struct ksmbd_conn * for (i = 0; i < num_aces; i++) { int pace_size; - if (offsetof(struct smb_ace, access_req) > aces_size) + if (aces_size < offsetof(struct smb_ace, sid) + + CIFS_SID_BASE_SIZE) break; pace_size = le16_to_cpu(parent_aces->size); - if (pace_size > aces_size) + if (pace_size > aces_size || + pace_size < offsetof(struct smb_ace, sid) + + CIFS_SID_BASE_SIZE) break; aces_size -= pace_size;