diff --git a/Documentation/filesystems/fsverity.rst b/Documentation/filesystems/fsverity.rst index 13e4b18e5dbb..362b7a5dc300 100644 --- a/Documentation/filesystems/fsverity.rst +++ b/Documentation/filesystems/fsverity.rst @@ -86,6 +86,14 @@ authenticating fs-verity file hashes include: signature in their "security.ima" extended attribute, as controlled by the IMA policy. For more information, see the IMA documentation. +- Integrity Policy Enforcement (IPE). IPE supports enforcing access + control decisions based on immutable security properties of files, + including those protected by fs-verity's built-in signatures. + "IPE policy" specifically allows for the authorization of fs-verity + files using properties ``fsverity_digest`` for identifying + files by their verity digest, and ``fsverity_signature`` to authorize + files with a verified fs-verity's built-in signature. + - Trusted userspace code in combination with `Built-in signature verification`_. This approach should be used only with great care. @@ -457,7 +465,11 @@ Enabling this option adds the following: On success, the ioctl persists the signature alongside the Merkle tree. Then, any time the file is opened, the kernel verifies the file's actual digest against this signature, using the certificates - in the ".fs-verity" keyring. + in the ".fs-verity" keyring. This verification happens as long as the + file's signature exists, regardless of the state of the sysctl variable + "fs.verity.require_signatures" described in the next item. The IPE LSM + relies on this behavior to recognize and label fsverity files + that contain a verified built-in fsverity signature. 3. A new sysctl "fs.verity.require_signatures" is made available. When set to 1, the kernel requires that all verity files have a @@ -481,7 +493,7 @@ be carefully considered before using them: - Builtin signature verification does *not* make the kernel enforce that any files actually have fs-verity enabled. Thus, it is not a - complete authentication policy. Currently, if it is used, the only + complete authentication policy. Currently, if it is used, one way to complete the authentication policy is for trusted userspace code to explicitly check whether files have fs-verity enabled with a signature before they are accessed. (With @@ -490,6 +502,13 @@ be carefully considered before using them: could just store the signature alongside the file and verify it itself using a cryptographic library, instead of using this feature. +- Another approach is to utilize fs-verity builtin signature + verification in conjunction with the IPE LSM, which supports defining + a kernel-enforced, system-wide authentication policy that allows only + files with a verified fs-verity builtin signature to perform certain + operations, such as execution. Note that IPE doesn't require + fs.verity.require_signatures=1. + - A file's builtin signature can only be set at the same time that fs-verity is being enabled on the file. Changing or deleting the builtin signature later requires re-creating the file. diff --git a/fs/verity/signature.c b/fs/verity/signature.c index 90c07573dd77..0302a4e506ec 100644 --- a/fs/verity/signature.c +++ b/fs/verity/signature.c @@ -17,6 +17,7 @@ #include #include +#include #include #include @@ -41,7 +42,11 @@ static struct key *fsverity_keyring; * @sig_size: size of signature in bytes, or 0 if no signature * * If the file includes a signature of its fs-verity file digest, verify it - * against the certificates in the fs-verity keyring. + * against the certificates in the fs-verity keyring. Note that signatures + * are verified regardless of the state of the 'fsverity_require_signatures' + * variable and the LSM subsystem relies on this behavior to help enforce + * file integrity policies. Please discuss changes with the LSM list + * (thank you!). * * Return: 0 on success (signature valid or not required); -errno on failure */ @@ -106,6 +111,17 @@ int fsverity_verify_signature(const struct fsverity_info *vi, return err; } + err = security_inode_setintegrity(inode, + LSM_INT_FSVERITY_BUILTINSIG_VALID, + signature, + sig_size); + + if (err) { + fsverity_err(inode, "Error %d exposing file signature to LSMs", + err); + return err; + } + return 0; } diff --git a/include/linux/security.h b/include/linux/security.h index 97b7c57e6560..c37c32ebbdcd 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -92,6 +92,7 @@ struct dm_verity_digest { enum lsm_integrity_type { LSM_INT_DMVERITY_SIG_VALID, LSM_INT_DMVERITY_ROOTHASH, + LSM_INT_FSVERITY_BUILTINSIG_VALID, }; /*