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authorEric Biggers <ebiggers@google.com>2023-06-12 22:00:47 +0300
committerEric Biggers <ebiggers@google.com>2023-06-14 20:41:07 +0300
commit74836ecbc5c7565d24a770917644e96af3e98d25 (patch)
tree097ae681bdb906c38d3da394b388fc17de5b71e3
parent13e2408d02dd12a3b46bf8a29b3ae4f6119fc520 (diff)
downloadlinux-74836ecbc5c7565d24a770917644e96af3e98d25.tar.xz
fsverity: rework fsverity_get_digest() again
Address several issues with the calling convention and documentation of fsverity_get_digest(): - Make it provide the hash algorithm as either a FS_VERITY_HASH_ALG_* value or HASH_ALGO_* value, at the caller's choice, rather than only a HASH_ALGO_* value as it did before. This allows callers to work with the fsverity native algorithm numbers if they want to. HASH_ALGO_* is what IMA uses, but other users (e.g. overlayfs) should use FS_VERITY_HASH_ALG_* to match fsverity-utils and the fsverity UAPI. - Make it return the digest size so that it doesn't need to be looked up separately. Use the return value for this, since 0 works nicely for the "file doesn't have fsverity enabled" case. This also makes it clear that no other errors are possible. - Rename the 'digest' parameter to 'raw_digest' and clearly document that it is only useful in combination with the algorithm ID. This hopefully clears up a point of confusion. - Export it to modules, since overlayfs will need it for checking the fsverity digests of lowerdata files (https://lore.kernel.org/r/dd294a44e8f401e6b5140029d8355f88748cd8fd.1686565330.git.alexl@redhat.com). Acked-by: Mimi Zohar <zohar@linux.ibm.com> # for the IMA piece Link: https://lore.kernel.org/r/20230612190047.59755-1-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
-rw-r--r--fs/verity/measure.c37
-rw-r--r--include/linux/fsverity.h14
-rw-r--r--security/integrity/ima/ima_api.c31
3 files changed, 47 insertions, 35 deletions
diff --git a/fs/verity/measure.c b/fs/verity/measure.c
index 5c79ea1b2468..eec5956141da 100644
--- a/fs/verity/measure.c
+++ b/fs/verity/measure.c
@@ -61,27 +61,42 @@ EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
/**
* fsverity_get_digest() - get a verity file's digest
* @inode: inode to get digest of
- * @digest: (out) pointer to the digest
- * @alg: (out) pointer to the hash algorithm enumeration
+ * @raw_digest: (out) the raw file digest
+ * @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value
+ * @halg: (out) the digest's algorithm, as a HASH_ALGO_* value
*
- * Return the file hash algorithm and digest of an fsverity protected file.
- * Assumption: before calling this, the file must have been opened.
+ * Retrieves the fsverity digest of the given file. The file must have been
+ * opened at least once since the inode was last loaded into the inode cache;
+ * otherwise this function will not recognize when fsverity is enabled.
*
- * Return: 0 on success, -errno on failure
+ * The file's fsverity digest consists of @raw_digest in combination with either
+ * @alg or @halg. (The caller can choose which one of @alg or @halg to use.)
+ *
+ * IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since
+ * @raw_digest is meaningless without knowing which algorithm it uses! fsverity
+ * provides no security guarantee for users who ignore the algorithm ID, even if
+ * they use the digest size (since algorithms can share the same digest size).
+ *
+ * Return: The size of the raw digest in bytes, or 0 if the file doesn't have
+ * fsverity enabled.
*/
int fsverity_get_digest(struct inode *inode,
- u8 digest[FS_VERITY_MAX_DIGEST_SIZE],
- enum hash_algo *alg)
+ u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
+ u8 *alg, enum hash_algo *halg)
{
const struct fsverity_info *vi;
const struct fsverity_hash_alg *hash_alg;
vi = fsverity_get_info(inode);
if (!vi)
- return -ENODATA; /* not a verity file */
+ return 0; /* not a verity file */
hash_alg = vi->tree_params.hash_alg;
- memcpy(digest, vi->file_digest, hash_alg->digest_size);
- *alg = hash_alg->algo_id;
- return 0;
+ memcpy(raw_digest, vi->file_digest, hash_alg->digest_size);
+ if (alg)
+ *alg = hash_alg - fsverity_hash_algs;
+ if (halg)
+ *halg = hash_alg->algo_id;
+ return hash_alg->digest_size;
}
+EXPORT_SYMBOL_GPL(fsverity_get_digest);
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index e76605d5b36e..1eb7eae580be 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -143,8 +143,8 @@ int fsverity_ioctl_enable(struct file *filp, const void __user *arg);
int fsverity_ioctl_measure(struct file *filp, void __user *arg);
int fsverity_get_digest(struct inode *inode,
- u8 digest[FS_VERITY_MAX_DIGEST_SIZE],
- enum hash_algo *alg);
+ u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
+ u8 *alg, enum hash_algo *halg);
/* open.c */
@@ -197,10 +197,14 @@ static inline int fsverity_ioctl_measure(struct file *filp, void __user *arg)
}
static inline int fsverity_get_digest(struct inode *inode,
- u8 digest[FS_VERITY_MAX_DIGEST_SIZE],
- enum hash_algo *alg)
+ u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
+ u8 *alg, enum hash_algo *halg)
{
- return -EOPNOTSUPP;
+ /*
+ * fsverity is not enabled in the kernel configuration, so always report
+ * that the file doesn't have fsverity enabled (digest size 0).
+ */
+ return 0;
}
/* open.c */
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index d3662f4acadc..ce541b0ee1d3 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -202,19 +202,19 @@ int ima_get_action(struct mnt_idmap *idmap, struct inode *inode,
allowed_algos);
}
-static int ima_get_verity_digest(struct integrity_iint_cache *iint,
- struct ima_max_digest_data *hash)
+static bool ima_get_verity_digest(struct integrity_iint_cache *iint,
+ struct ima_max_digest_data *hash)
{
- enum hash_algo verity_alg;
- int ret;
+ enum hash_algo alg;
+ int digest_len;
/*
* On failure, 'measure' policy rules will result in a file data
* hash containing 0's.
*/
- ret = fsverity_get_digest(iint->inode, hash->digest, &verity_alg);
- if (ret)
- return ret;
+ digest_len = fsverity_get_digest(iint->inode, hash->digest, NULL, &alg);
+ if (digest_len == 0)
+ return false;
/*
* Unlike in the case of actually calculating the file hash, in
@@ -223,9 +223,9 @@ static int ima_get_verity_digest(struct integrity_iint_cache *iint,
* mismatch between the verity algorithm and the xattr signature
* algorithm, if one exists, will be detected later.
*/
- hash->hdr.algo = verity_alg;
- hash->hdr.length = hash_digest_size[verity_alg];
- return 0;
+ hash->hdr.algo = alg;
+ hash->hdr.length = digest_len;
+ return true;
}
/*
@@ -276,16 +276,9 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
memset(&hash.digest, 0, sizeof(hash.digest));
if (iint->flags & IMA_VERITY_REQUIRED) {
- result = ima_get_verity_digest(iint, &hash);
- switch (result) {
- case 0:
- break;
- case -ENODATA:
+ if (!ima_get_verity_digest(iint, &hash)) {
audit_cause = "no-verity-digest";
- break;
- default:
- audit_cause = "invalid-verity-digest";
- break;
+ result = -ENODATA;
}
} else if (buf) {
result = ima_calc_buffer_hash(buf, size, &hash.hdr);