From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f70.google.com (mail-ej1-f70.google.com [209.85.218.70]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0319D43CEDD for ; Fri, 31 Jul 2026 15:44:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.70 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785512650; cv=none; b=ZnSHjkKKaUK6M+iNF+kPzqlQFUmSCvCVvsZNpwg6cgjPjZ28rRK4zIRxnNRIXmW8WZ7MuyG5ILdohF6kino7npHLOyJn7tO0QpBCemajXmEBOqP1mFGka+KAKqboI8B9zaVMkfLb0RyEdxkmgPMyEDcnoph8mdiSZMVQFBcNMGA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785512650; c=relaxed/simple; bh=LEWxUOWVmU3Vw6HcaHSqImiVNkdfMh5fMNn+ukIuvOU=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=JToCmfxd+lIWbNnSGReulniQHvn4pdMJH1z4O0LUrVi2v9BXdvnOwMYDq+8M1rtyNj0Rb/F+cdUmePK5wFDL2OpiGq66pweicCP2V8na1NJJSx9jiqcmbTi7Qw2gnX+scBZ7Gs06Hb7u1NQwRP1oGkV5DLkd7p/3BUUoUezpIOU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--gnoack.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=LbHGyfz2; arc=none smtp.client-ip=209.85.218.70 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--gnoack.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="LbHGyfz2" Received: by mail-ej1-f70.google.com with SMTP id a640c23a62f3a-c15ce19923fso102889866b.3 for ; Fri, 31 Jul 2026 08:44:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1785512647; x=1786117447; darn=vger.kernel.org; h=content-transfer-encoding:content-type:cc:to:from:subject :message-id:references:mime-version:in-reply-to:date:from:to:cc :subject:date:message-id:reply-to:content-type; bh=TGv9oaNlaBZk+/EC49Nn/fhRApP+RDWSQ21AKhDj5YQ=; b=LbHGyfz2fJvWGryBs0jfvghnzvaFPq/hvkqIzfRL2Mi2Cei+ejj+jisVbwI1wNs6SW VyZTRAD+2w9B4z+G+kIG2M/9DwKNsvbW7bBEAPf+5qcxQhZDNJ58cNKD8IQoMc62PJY5 OmwqDQOYt3KO3F54n10stuVTHmHIKJ1FOxKypQ6vDEprSv/RTn3kYthIb9EaQrbQPfuW MP28fVKdzCgrmJQNEgrFzOHsvB9znYvMVUHS3L2bqyhyh3hLEC7Kzyl6JPbjYHS9FxHT qOgmX0no0RAmN/znmiMySgUobjba7MFqid4DuNLg8ZpMwL6Vf404l1tQDxjjYriDL9zs 4sTw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785512647; x=1786117447; h=content-transfer-encoding:content-type:cc:to:from:subject :message-id:references:mime-version:in-reply-to:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=TGv9oaNlaBZk+/EC49Nn/fhRApP+RDWSQ21AKhDj5YQ=; b=m/DKmPUwETucEp/zTd12+A+no0zEDoSBLDth/8WZ7BG4C01SPVu278tCKRsjtU6PPG qPhS/pf9PRk6r/9Sq5snai+Di38DbgvWBvkWQgteCJfzHsaq43FJAlmMpCS57fkILLrM o13GsiovSqGp1Y0gJUIhk8taAKpHYnQ8mG4yGAiA6wH1m4vZlGCQLKVfFmPaiFh0ZG9S Q0LSVzwpea/kvTIXxHoFiQQGsAa+MFXeAmDjJMD5HP9YdKc/MMmHJmZiv6dB1CtWawd4 S2n2jrhtIp+1FSqxmd+eOWXHu7Yp4Dxp4zZZV48o4zrbcPEIKHM5qe+u8W0zwDkZh88w mwwg== X-Gm-Message-State: AOJu0YyMejO4bfej44lUSHXYfpcAQz50Kpg3TOjO6EJM5ElbnMCR4ci/ 3rNK4E57P1A3e78387elrd2mUAj4J77vQ2H7gJRf4Iq+ukmPlH2PdBHb0vvJ+nSn4tLG2Gl1TGc DRfNE8w== X-Received: from wrtr6.prod.google.com ([2002:a5d:4e46:0:b0:47f:44b6:2328]) (user=gnoack job=prod-delivery.src-stubby-dispatcher) by 2002:a17:906:f598:b0:c1c:2173:d412 with SMTP id a640c23a62f3a-c1fe8494f9amr3013166b.1.1785512646788; Fri, 31 Jul 2026 08:44:06 -0700 (PDT) Date: Fri, 31 Jul 2026 17:43:50 +0200 In-Reply-To: <20260731154353.1790268-1-gnoack@google.com> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260731154353.1790268-1-gnoack@google.com> X-Mailer: git-send-email 2.55.0.508.g3f0d502094-goog Message-ID: <20260731154353.1790268-3-gnoack@google.com> Subject: [PATCH v5 2/5] landlock: Require LANDLOCK_ACCESS_FS_MAKE_REG for whiteout creation From: "=?UTF-8?q?G=C3=BCnther=20Noack?=" To: "=?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?=" , Christian Brauner Cc: linux-security-module@vger.kernel.org, Paul Moore , Amir Goldstein , Miklos Szeredi , Serge Hallyn , Stephen Smalley , "=?UTF-8?q?G=C3=BCnther=20Noack?=" , stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Whiteout objects are used in the upper layer of an OverlayFS to indicate that the file with this name does not exist in the unified view, even if it is present in one of the lower layer file systems. For the userspace implementations of OverlayFS (fuse-overlayfs), whiteout objects can be created from userspace as well: * mknod(2) with S_IFCHR and makedev(0, 0) * renameat2(2) with RENAME_WHITEOUT, creating the whiteout in the old place of the moved file. This commit guards whiteout creation in both of these cases with LANDLOCK_ACCESS_FS_MAKE_REG. Whiteout objects are *not* considered character devices and are not bound to a driver. For the mknod(2) case, introduce a Landlock erratum. The creation of whiteout objects through mknod(2) was previously guarded using LANDLOCK_ACCESS_FS_MAKE_CHAR, and it is now guarded using LANDLOCK_ACCESS_MAKE_REG. For the renameat2(2) case, fix a bug: Before this commit, renameat2(2) with RENAME_WHITEOUT would create a directory entry even when all LANDLOCK_ACCESS_FS_MAKE_* rights were denied. This does not affect normal renames within layered OverlayFS mounts: When doing a regular rename() on a mounted fuse-overlayfs, it is the fuse-overlayfs daemon that exercises renameat2() with RENAME_WHITEOUT, and only the Landlock domain of that daemon is checked there. Suggested-by: Christian Brauner Suggested-by: Micka=C3=ABl Sala=C3=BCn Cc: stable@vger.kernel.org Fixes: cb2c7d1a1776 ("landlock: Support filesystem access-control") Depends-on: 49c9e09d9610 ("landlock: Fix handling of disconnected directori= es") Depends-on: fe72ce6710cb ("landlock: Add errata documentation section") Signed-off-by: G=C3=BCnther Noack --- include/uapi/linux/landlock.h | 1 + security/landlock/errata/abi-1.h | 23 ++++++++++++++++++ security/landlock/fs.c | 41 +++++++++++++++++++++++++------- 3 files changed, 56 insertions(+), 9 deletions(-) diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index 7ffe2ef127ee..9c1102ebf06e 100644 --- a/include/uapi/linux/landlock.h +++ b/include/uapi/linux/landlock.h @@ -351,6 +351,7 @@ struct landlock_net_port_attr { * device. * - %LANDLOCK_ACCESS_FS_MAKE_DIR: Create (or rename) a directory. * - %LANDLOCK_ACCESS_FS_MAKE_REG: Create (or rename or link) a regular fi= le. + * This also guards the creation of whiteout objects as used in OverlayF= S. * - %LANDLOCK_ACCESS_FS_MAKE_SOCK: Create (or rename or link) a UNIX doma= in * socket. * - %LANDLOCK_ACCESS_FS_MAKE_FIFO: Create (or rename or link) a named pip= e. diff --git a/security/landlock/errata/abi-1.h b/security/landlock/errata/ab= i-1.h index 3f099555f059..e0d543d9d508 100644 --- a/security/landlock/errata/abi-1.h +++ b/security/landlock/errata/abi-1.h @@ -22,3 +22,26 @@ * from their original mount points. */ LANDLOCK_ERRATUM(3) + +/** + * DOC: erratum_4 + * + * Erratum 4: Creation of whiteout objects + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * + * This fix changes the access rights required for the creation of whiteou= t + * objects through :manpage:`mknod(2)` or :manpage:`renameat2(2)`. Creati= ng + * whiteout objects is now guarded by ``LANDLOCK_ACCESS_FS_MAKE_REG`` inst= ead of + * ``LANDLOCK_ACCESS_FS_MAKE_CHAR``. + * + * Whiteout objects are used in OverlayFS to mark the absence of a file in= an + * upper file system. Despite being created with ``S_IFCHR``, whiteout ob= jects + * do not count as character devices. + * + * Impact: + * + * Sandboxed programs that create OverlayFS whiteouts (such as fuse-overla= yfs) + * now require ``LANDLOCK_ACCESS_FS_MAKE_REG`` instead of + * ``LANDLOCK_ACCESS_FS_MAKE_CHAR``. + */ +LANDLOCK_ERRATUM(4) diff --git a/security/landlock/fs.c b/security/landlock/fs.c index f7e5e4ef9eac..c12af17cac9e 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -20,6 +20,7 @@ #include #include #include +#include #include #include #include @@ -983,7 +984,8 @@ static int current_check_access_path(const struct path = *const path, return -EACCES; } =20 -static __attribute_const__ access_mask_t get_mode_access(const umode_t mod= e) +static __attribute_const__ access_mask_t get_mode_access(const umode_t mod= e, + const dev_t dev) { switch (mode & S_IFMT) { case S_IFLNK: @@ -991,6 +993,9 @@ static __attribute_const__ access_mask_t get_mode_acces= s(const umode_t mode) case S_IFDIR: return LANDLOCK_ACCESS_FS_MAKE_DIR; case S_IFCHR: + /* Whiteout objects are guarded with MAKE_REG. */ + if (dev =3D=3D WHITEOUT_DEV) + return LANDLOCK_ACCESS_FS_MAKE_REG; return LANDLOCK_ACCESS_FS_MAKE_CHAR; case S_IFBLK: return LANDLOCK_ACCESS_FS_MAKE_BLOCK; @@ -1007,6 +1012,13 @@ static __attribute_const__ access_mask_t get_mode_ac= cess(const umode_t mode) } } =20 +static __attribute_const__ access_mask_t +get_dentry_access(const struct dentry *const dentry) +{ + return get_mode_access(d_backing_inode(dentry)->i_mode, + d_backing_inode(dentry)->i_rdev); +} + static access_mask_t maybe_remove(const struct dentry *const dentry) { if (d_is_negative(dentry)) @@ -1093,6 +1105,7 @@ static bool collect_domain_accesses(const struct land= lock_ruleset *const domain, * @new_dentry: Destination file or directory. * @removable: Sets to true if it is a rename operation. * @exchange: Sets to true if it is a rename operation with RENAME_EXCHANG= E. + * @whiteout: Sets to true if it is a rename operation with RENAME_WHITEOU= T. * * Because of its unprivileged constraints, Landlock relies on file hierar= chies * (and not only inodes) to tie access rights to files. Being able to lin= k or @@ -1140,7 +1153,8 @@ static bool collect_domain_accesses(const struct land= lock_ruleset *const domain, static int current_check_refer_path(struct dentry *const old_dentry, const struct path *const new_dir, struct dentry *const new_dentry, - const bool removable, const bool exchange) + const bool removable, const bool exchange, + const bool whiteout) { const struct landlock_cred_security *const subject =3D landlock_get_applicable_subject(current_cred(), any_fs, NULL); @@ -1159,18 +1173,25 @@ static int current_check_refer_path(struct dentry *= const old_dentry, if (exchange) { if (unlikely(d_is_negative(new_dentry))) return -ENOENT; - access_request_parent1 =3D - get_mode_access(d_backing_inode(new_dentry)->i_mode); + access_request_parent1 =3D get_dentry_access(new_dentry); } else { access_request_parent1 =3D 0; } - access_request_parent2 =3D - get_mode_access(d_backing_inode(old_dentry)->i_mode); + access_request_parent2 =3D get_dentry_access(old_dentry); if (removable) { access_request_parent1 |=3D maybe_remove(old_dentry); access_request_parent2 |=3D maybe_remove(new_dentry); } =20 + /* + * In case of renameat2(2) with RENAME_WHITEOUT, a whiteout object is + * created in the source location, so we require an additional access + * right there. + */ + if (whiteout) + access_request_parent1 |=3D + get_mode_access(S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV); + /* The mount points are the same for old and new paths, cf. EXDEV. */ if (old_dentry->d_parent =3D=3D new_dir->dentry) { /* @@ -1520,7 +1541,7 @@ static int hook_path_link(struct dentry *const old_de= ntry, struct dentry *const new_dentry) { return current_check_refer_path(old_dentry, new_dir, new_dentry, false, - false); + false, false); } =20 static int hook_path_rename(const struct path *const old_dir, @@ -1531,7 +1552,8 @@ static int hook_path_rename(const struct path *const = old_dir, { /* old_dir refers to old_dentry->d_parent and new_dir->mnt */ return current_check_refer_path(old_dentry, new_dir, new_dentry, true, - !!(flags & RENAME_EXCHANGE)); + !!(flags & RENAME_EXCHANGE), + !!(flags & RENAME_WHITEOUT)); } =20 static int hook_path_mkdir(const struct path *const dir, @@ -1544,7 +1566,8 @@ static int hook_path_mknod(const struct path *const d= ir, struct dentry *const dentry, const umode_t mode, const unsigned int dev) { - return current_check_access_path(dir, get_mode_access(mode)); + return current_check_access_path( + dir, get_mode_access(mode, new_decode_dev(dev))); } =20 static int hook_path_symlink(const struct path *const dir, --=20 2.55.0.508.g3f0d502094-goog