| Message ID | 20230820173237.2579-1-ebiggers@kernel.org (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [v3] fsverity: skip PKCS#7 parser when keyring is empty | expand |
On Sun Aug 20, 2023 at 8:32 PM EEST, Eric Biggers wrote: > From: Eric Biggers <ebiggers@google.com> > > If an fsverity builtin signature is given for a file but the > ".fs-verity" keyring is empty, there's no real reason to run the PKCS#7 > parser. Skip this to avoid the PKCS#7 attack surface when builtin > signature support is configured into the kernel but is not being used. > > This is a hardening improvement, not a fix per se, but I've added > Fixes and Cc stable to get it out to more users. > > Fixes: 432434c9f8e1 ("fs-verity: support builtin file signatures") > Cc: stable@vger.kernel.org > Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> > Signed-off-by: Eric Biggers <ebiggers@google.com> > --- > > v3: improve the error message slightly > v2: check keyring and return early before allocating formatted digest > > fs/verity/signature.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/fs/verity/signature.c b/fs/verity/signature.c > index b95acae64eac6..90c07573dd77b 100644 > --- a/fs/verity/signature.c > +++ b/fs/verity/signature.c > @@ -55,20 +55,36 @@ int fsverity_verify_signature(const struct fsverity_info *vi, > > if (sig_size == 0) { > if (fsverity_require_signatures) { > fsverity_err(inode, > "require_signatures=1, rejecting unsigned file!"); > return -EPERM; > } > return 0; > } > > + if (fsverity_keyring->keys.nr_leaves_on_tree == 0) { > + /* > + * The ".fs-verity" keyring is empty, due to builtin signatures > + * being supported by the kernel but not actually being used. > + * In this case, verify_pkcs7_signature() would always return an > + * error, usually ENOKEY. It could also be EBADMSG if the > + * PKCS#7 is malformed, but that isn't very important to > + * distinguish. So, just skip to ENOKEY to avoid the attack > + * surface of the PKCS#7 parser, which would otherwise be > + * reachable by any task able to execute FS_IOC_ENABLE_VERITY. > + */ > + fsverity_err(inode, > + "fs-verity keyring is empty, rejecting signed file!"); > + return -ENOKEY; > + } > + > d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL); > if (!d) > return -ENOMEM; > memcpy(d->magic, "FSVerity", 8); > d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs); > d->digest_size = cpu_to_le16(hash_alg->digest_size); > memcpy(d->digest, vi->file_digest, hash_alg->digest_size); > > err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size, > signature, sig_size, fsverity_keyring, > > base-commit: 456ae5fe9b448f44ebe98b391a3bae9c75df465e > -- > 2.41.0 Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> BR, Jarkko
diff --git a/fs/verity/signature.c b/fs/verity/signature.c index b95acae64eac6..90c07573dd77b 100644 --- a/fs/verity/signature.c +++ b/fs/verity/signature.c @@ -55,20 +55,36 @@ int fsverity_verify_signature(const struct fsverity_info *vi, if (sig_size == 0) { if (fsverity_require_signatures) { fsverity_err(inode, "require_signatures=1, rejecting unsigned file!"); return -EPERM; } return 0; } + if (fsverity_keyring->keys.nr_leaves_on_tree == 0) { + /* + * The ".fs-verity" keyring is empty, due to builtin signatures + * being supported by the kernel but not actually being used. + * In this case, verify_pkcs7_signature() would always return an + * error, usually ENOKEY. It could also be EBADMSG if the + * PKCS#7 is malformed, but that isn't very important to + * distinguish. So, just skip to ENOKEY to avoid the attack + * surface of the PKCS#7 parser, which would otherwise be + * reachable by any task able to execute FS_IOC_ENABLE_VERITY. + */ + fsverity_err(inode, + "fs-verity keyring is empty, rejecting signed file!"); + return -ENOKEY; + } + d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL); if (!d) return -ENOMEM; memcpy(d->magic, "FSVerity", 8); d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs); d->digest_size = cpu_to_le16(hash_alg->digest_size); memcpy(d->digest, vi->file_digest, hash_alg->digest_size); err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size, signature, sig_size, fsverity_keyring,