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GET /api/1.1/patches/2224697/?format=api
{ "id": 2224697, "url": "http://patchwork.ozlabs.org/api/1.1/patches/2224697/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linux-cifs-client/patch/20260417184557.1138554-1-michael.bommarito@gmail.com/", "project": { "id": 12, "url": "http://patchwork.ozlabs.org/api/1.1/projects/12/?format=api", "name": "Linux CIFS Client", "link_name": "linux-cifs-client", "list_id": "linux-cifs.vger.kernel.org", "list_email": "linux-cifs@vger.kernel.org", "web_url": "", "scm_url": "", "webscm_url": "" }, "msgid": "<20260417184557.1138554-1-michael.bommarito@gmail.com>", "date": "2026-04-17T18:45:57", "name": "[v2] ksmbd: validate num_aces and harden ACE walk in smb_inherit_dacl()", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "e55b978473b36c3497f46148e87a82ea38b1bdb1", "submitter": { "id": 93078, "url": "http://patchwork.ozlabs.org/api/1.1/people/93078/?format=api", "name": "Michael Bommarito", "email": "michael.bommarito@gmail.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/linux-cifs-client/patch/20260417184557.1138554-1-michael.bommarito@gmail.com/mbox/", "series": [ { "id": 500389, "url": "http://patchwork.ozlabs.org/api/1.1/series/500389/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linux-cifs-client/list/?series=500389", "date": "2026-04-17T18:45:57", "name": "[v2] ksmbd: validate num_aces and harden ACE walk in smb_inherit_dacl()", "version": 2, "mbox": "http://patchwork.ozlabs.org/series/500389/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2224697/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2224697/checks/", "tags": {}, "headers": { "Return-Path": "\n <linux-cifs+bounces-10893-incoming=patchwork.ozlabs.org@vger.kernel.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "linux-cifs@vger.kernel.org" ], "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=FSYI0g4n;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org\n (client-ip=2600:3c0a:e001:db::12fc:5321; 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This causes a ~8 MB allocation (not kzalloc, so\nuninitialized) that the subsequent loop only partially populates, and\nmay also overflow the three-way size_t multiply on 32-bit kernels.\n\nAdditionally, the ACE walk loop uses the weaker\noffsetof(struct smb_ace, access_req) minimum size check rather than\nthe minimum valid on-wire ACE size, and does not reject ACEs whose\ndeclared size is below the minimum.\n\nReproduced on UML + KASAN + LOCKDEP against the real ksmbd code path.\nA legitimate mount.cifs client creates a parent directory over SMB\n(ksmbd writes a valid security.NTACL xattr), then the NTACL blob on\nthe backing filesystem is rewritten to set num_aces = 0xFFFF while\nkeeping the posix_acl_hash bytes intact so ksmbd_vfs_get_sd_xattr()'s\nhash check still passes. A subsequent SMB2 CREATE of a child under\nthat parent drives smb2_open() into smb_inherit_dacl() (share has\n\"vfs objects = acl_xattr\" set), which fails the page allocator:\n\n WARNING: mm/page_alloc.c:5226 at __alloc_frozen_pages_noprof+0x46c/0x9c0\n Workqueue: ksmbd-io handle_ksmbd_work\n __alloc_frozen_pages_noprof+0x46c/0x9c0\n ___kmalloc_large_node+0x68/0x130\n __kmalloc_large_node_noprof+0x24/0x70\n __kmalloc_noprof+0x4c9/0x690\n smb_inherit_dacl+0x394/0x2430\n smb2_open+0x595d/0xabe0\n handle_ksmbd_work+0x3d3/0x1140\n\nWith the patch applied the added guard rejects the tampered value\nwith -EINVAL before any large allocation runs, smb2_open() falls back\nto smb2_create_sd_buffer(), and the child is created with a default\nSD. No warning, no splat.\n\nFix by:\n\n 1. Validating num_aces against pdacl_size using the same formula\n applied in parse_dacl().\n\n 2. Replacing the raw kmalloc(sizeof * num_aces * 2) with\n kmalloc_array(num_aces * 2, sizeof(...)) for overflow-safe\n allocation.\n\n 3. Tightening the per-ACE loop guard to require the minimum valid\n ACE size (offsetof(smb_ace, sid) + CIFS_SID_BASE_SIZE) and\n rejecting under-sized ACEs, matching the hardening in\n smb_check_perm_dacl() and parse_dacl().\n\nv1 -> v2:\n - Replace the synthetic test-module splat in the changelog with a\n real-path UML + KASAN reproduction driven through mount.cifs and\n SMB2 CREATE; Namjae flagged the kcifs3_test_inherit_dacl_old name\n in v1 since it does not exist in ksmbd.\n - Drop the commit-hash citation from the code comment per Namjae's\n review; keep the parse_dacl() pointer.\n\nFixes: e2f34481b24d (\"cifsd: add server-side procedures for SMB3\")\nCc: stable@vger.kernel.org\nAssisted-by: Claude:claude-opus-4-6\nSigned-off-by: Michael Bommarito <michael.bommarito@gmail.com>\n---\n fs/smb/server/smbacl.c | 28 +++++++++++++++++++++++-----\n 1 file changed, 23 insertions(+), 5 deletions(-)", "diff": "diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c\nindex d5943256c071..4a341c1f6630 100644\n--- a/fs/smb/server/smbacl.c\n+++ b/fs/smb/server/smbacl.c\n@@ -1105,8 +1105,24 @@ int smb_inherit_dacl(struct ksmbd_conn *conn,\n \t\tgoto free_parent_pntsd;\n \t}\n \n-\taces_base = kmalloc(sizeof(struct smb_ace) * num_aces * 2,\n-\t\t\t KSMBD_DEFAULT_GFP);\n+\taces_size = pdacl_size - sizeof(struct smb_acl);\n+\n+\t/*\n+\t * Validate num_aces against the DACL payload before allocating.\n+\t * Each ACE must be at least as large as its fixed-size header\n+\t * (up to the SID base), so num_aces cannot exceed the payload\n+\t * divided by the minimum ACE size. This mirrors the existing\n+\t * check in parse_dacl().\n+\t */\n+\tif (num_aces > aces_size / (offsetof(struct smb_ace, sid) +\n+\t\t\t\t offsetof(struct smb_sid, sub_auth) +\n+\t\t\t\t sizeof(__le16))) {\n+\t\trc = -EINVAL;\n+\t\tgoto free_parent_pntsd;\n+\t}\n+\n+\taces_base = kmalloc_array(num_aces * 2, sizeof(struct smb_ace),\n+\t\t\t\t KSMBD_DEFAULT_GFP);\n \tif (!aces_base) {\n \t\trc = -ENOMEM;\n \t\tgoto free_parent_pntsd;\n@@ -1115,7 +1131,6 @@ int smb_inherit_dacl(struct ksmbd_conn *conn,\n \taces = (struct smb_ace *)aces_base;\n \tparent_aces = (struct smb_ace *)((char *)parent_pdacl +\n \t\t\tsizeof(struct smb_acl));\n-\taces_size = acl_len - sizeof(struct smb_acl);\n \n \tif (pntsd_type & DACL_AUTO_INHERITED)\n \t\tinherited_flags = INHERITED_ACE;\n@@ -1123,11 +1138,14 @@ int smb_inherit_dacl(struct ksmbd_conn *conn,\n \tfor (i = 0; i < num_aces; i++) {\n \t\tint pace_size;\n \n-\t\tif (offsetof(struct smb_ace, access_req) > aces_size)\n+\t\tif (aces_size < offsetof(struct smb_ace, sid) +\n+\t\t CIFS_SID_BASE_SIZE)\n \t\t\tbreak;\n \n \t\tpace_size = le16_to_cpu(parent_aces->size);\n-\t\tif (pace_size > aces_size)\n+\t\tif (pace_size > aces_size ||\n+\t\t pace_size < offsetof(struct smb_ace, sid) +\n+\t\t\t\tCIFS_SID_BASE_SIZE)\n \t\t\tbreak;\n \n \t\taces_size -= pace_size;\n", "prefixes": [ "v2" ] }