From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792703753; b=nTDJ7p3TVKCRz1tOVh4hU6FTCSV47TTNGUPsZbR1czokdWFaaZ6rnmzzxW84VivsRLuY z/wjMabXDZ+uwj3ScT3TWjA4U0t1PoEBLcH/GQ0I53cFS6PLnV86FVehMEf8Al8qxniuT fWZYAQwIEa9mLyxCEHrvtDfLRYYendS6UsQaUZtB9Wh+aMN1WZqTfSDd7BEuG5/wCjX49 mu6Kmkom7qTteNtVWTuGa3ml3LciwbGdQ7sOCO4ffovoiMb2WecmN89q99NoDzvrO93ee 03yElyafd3HAiIEuCiBt5ItzaMYW4fu8m1PpnsdkQlb9+BT8Yj68DKjXIgwXOyPp1GQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792703753; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Transfer-Encoding; bh=ViygJGyeeKvJcEAVcpZEFMreWDoAi2NThaUnWrUztsE=; b=5HzW9eGmfD45exqcl2AIByZaXRNzeRHcoa/OatIgCVEaA1DN7+R02e9hLdh8mD/CnG1k UBb6+Hxm8SVv0BnuDgn3fOUd8vxiRJ5pjnzP4OOz1CL/yvcrkO5sp4SewY+Egq06q0EYn mQldIuIx406iLHlICl59uFPWswATpPRyOGFDGCrT26XbkxyJFEgR+7OIVPYJl9DNueZAP uIGw6whAna1kGg1+LkC6dioWVuHINqjOpm+WmP2BwGjGlfmgulTCIiqAlCWSD45bjzZvV dhkKFLnrnpX3Sxv5Zs0fDQ1tXwHJ88vk6UOCaBHTlNpHq/IlbsG1IFEgNYpE7ARtLmQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=SCxihNjW; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 50D6D606A319; Thu, 22 Oct 2026 21:15:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=SCxihNjW Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9C7851F01825; Thu, 22 Oct 2026 21:15:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792703752; bh=ViygJGyeeKvJcEAVcpZEFMreWDoAi2NThaUnWrUztsE=; h=From:To:Cc:Subject:Date; b=SCxihNjWYTJswMFE/aoaWYWaNtZCzWx2fkm9erpYMu+dRRYAe3HrLDW5k0Hs6PFF1 VGACzBA0gGUva6RmPUXAIWoAx3OAqQiVnTy4NSwiySXdxC85SrpOdir24N4cLCuofK peAS+eyD24b/1gcnIRHrYSMTXcBy21lAAFm6H/+ueZ4e6dVBp+F3iadh6yxnb5Tpp9 6AkmR1nig2lrI7aS0t0NHyUVvmDGFLEK52AlscxlnbSHd5KFaiHi7q4E+ILWpgt0cn O1BFkL+g30Mga4W6DpSbG5LDokarVsF+Y92ZyokYYSYFVrVAAYSzygP2nmXkAlDpuq OYb+oOKGBxVeQ== From: Eric Biggers To: fsverity@lists.linux.dev Cc: linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, Andrey Albershteyn , Eric Biggers , stable@vger.kernel.org Subject: [PATCH] fsverity: Explicitly require FMODE_READ to retrieve hashes Date: Thu, 22 Oct 2026 21:15:22 +0000 Message-ID: <20261022211522.1489943-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.56.0.307.g5fe7bd680c-goog X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The comment in fsverity_ioctl_read_metadata(), which justifies not checking for FMODE_READ, doesn't consider that the nonstandard access mode 3 (ioctl-only) exists. Opening an ioctl-only fd generally requires read (and write) permission. However, there are gaps with certain LSMs: an ioctl-only fd requests read (and write) permission via security_inode_permission, but not security_file_open. With certain LSMs relying on the latter, such as Landlock and AppArmor, an ioctl-only fd can be opened without the LSM granting read (and write) permission. Since FS_IOC_READ_VERITY_METADATA returns hashes of file contents blocks, it should require read permission. This also applies to FS_IOC_MEASURE_VERITY, which returns a hash for the whole file. Meanwhile, ioctl-only fds are a rarely-used feature, not known to be used with either ioctl. Therefore, just disallow these ioctls on ioctl-only file descriptors, similar to what was already done with FS_IOC_ENABLE_VERITY. More specifically, explicitly check for FMODE_READ. This also covers write-only fds to non-verity files which otherwise would have failed with ENODATA. This change in error code for write-only fds should be fine too, as these ioctls cannot be usefully used with write-only fds anyway, but it's worth noting as another technicality. Fixes: 4dd893d832cf ("fs-verity: implement FS_IOC_MEASURE_VERITY ioctl") Fixes: e17fe6579de0 ("fs-verity: add FS_IOC_READ_VERITY_METADATA ioctl") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers --- Documentation/filesystems/fsverity.rst | 3 +++ fs/verity/measure.c | 10 ++++++++++ fs/verity/read_metadata.c | 14 ++++++++++---- 3 files changed, 23 insertions(+), 4 deletions(-) diff --git a/Documentation/filesystems/fsverity.rst b/Documentation/filesystems/fsverity.rst index 22b49b295d1f9..e5d38439bf585 100644 --- a/Documentation/filesystems/fsverity.rst +++ b/Documentation/filesystems/fsverity.rst @@ -170,6 +170,7 @@ fatal signal), no changes are made to the file. FS_IOC_ENABLE_VERITY can fail with the following errors: - ``EACCES``: the process does not have write access to the file +- ``EBADF``: the file descriptor is not open for reading - ``EBADMSG``: the builtin signature is malformed - ``EBUSY``: this ioctl is already running on the file - ``EEXIST``: the file already has verity enabled @@ -232,6 +233,7 @@ regardless of the size of the file. FS_IOC_MEASURE_VERITY can fail with the following errors: +- ``EBADF``: the file descriptor is not open for reading - ``EFAULT``: the caller provided inaccessible memory - ``ENODATA``: the file is not a verity file - ``ENOTTY``: this type of filesystem does not implement fs-verity @@ -310,6 +312,7 @@ blocks from disk without actually verifying the path to the root node. FS_IOC_READ_VERITY_METADATA can fail with the following errors: +- ``EBADF``: the file descriptor is not open for reading - ``EFAULT``: the caller provided inaccessible memory - ``EINTR``: the ioctl was interrupted before any data was read - ``EINVAL``: reserved fields were set, or ``offset + length`` diff --git a/fs/verity/measure.c b/fs/verity/measure.c index 68dfccb697720..0c75616dca011 100644 --- a/fs/verity/measure.c +++ b/fs/verity/measure.c @@ -31,6 +31,16 @@ int fsverity_ioctl_measure(struct file *filp, void __user *_uarg) const struct fsverity_hash_alg *hash_alg; struct fsverity_digest arg; + /* + * This ioctl returns a hash of the file contents, so it should require + * read permission. Disallow it on ioctl-only (i.e., nonstandard access + * mode 3) fds, which can in some cases be acquired without passing all + * LSM read-permission checks. Also disallow write-only fds, which can + * refer only to non-verity files which would fail with ENODATA anyway. + */ + if (!(filp->f_mode & FMODE_READ)) + return -EBADF; + vi = fsverity_get_info(inode); if (!vi) return -ENODATA; /* not a verity file */ diff --git a/fs/verity/read_metadata.c b/fs/verity/read_metadata.c index b4c0892430cde..6694149f7b467 100644 --- a/fs/verity/read_metadata.c +++ b/fs/verity/read_metadata.c @@ -166,13 +166,19 @@ int fsverity_ioctl_read_metadata(struct file *filp, const void __user *uarg) int length; void __user *buf; + /* + * This ioctl returns file contents block hashes, so it should require + * read permission. Disallow it on ioctl-only (i.e., nonstandard access + * mode 3) fds, which can in some cases be acquired without passing all + * LSM read-permission checks. Also disallow write-only fds, which can + * refer only to non-verity files which would fail with ENODATA anyway. + */ + if (!(filp->f_mode & FMODE_READ)) + return -EBADF; + vi = fsverity_get_info(inode); if (!vi) return -ENODATA; /* not a verity file */ - /* - * Note that we don't have to explicitly check that the file is open for - * reading, since verity files can only be opened for reading. - */ if (copy_from_user(&arg, uarg, sizeof(arg))) return -EFAULT; base-commit: 7be4bc52fd9e0e55dc9a2e0232b89427d2c4b614 -- 2.56.0.307.g5fe7bd680c-goog