IMA wants to know what the hash of a file is, and currently does so by
reading the entire file and generating the hash. Some filesystems may
have the ability to store the hash in a secure manner resistant to
offline attacks (eg, filesystem-level file signing), and in that case
it's a performance win for IMA to be able to use that rather than having
to re-hash everything. This patch simply adds VFS-level support for
calling down to filesystems.
Signed-off-by: Matthew Garrett <mjg59@xxxxxxxxxx>
---
fs/read_write.c | 24 ++++++++++++++++++++++++
include/linux/fs.h | 6 +++++-
2 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/fs/read_write.c b/fs/read_write.c
index 39b4a21dd933..9ba3ce4bb838 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -2081,3 +2081,27 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same)
return ret;
}
EXPORT_SYMBOL(vfs_dedupe_file_range);
+
+/**
+ * vfs_gethash - obtain a file's hash
+ * @file: file structure in question
+ * @hash_algo: the hash algorithm requested
+ * @buf: buffer to return the hash in
+ * @size: size allocated for the buffer by the caller
+ *
+ * This function allows filesystems that support securely storing the hash
+ * of a file to return it rather than forcing the kernel to recalculate it.
+ * Filesystems that cannot provide guarantees about the hash being resistant
+ * to offline attack should not implement this functionality.
+ *
+ * Returns 0 on success, -EOPNOTSUPP if the filesystem doesn't support it.
+ */
+int vfs_get_hash(struct file *file, enum hash_algo hash, uint8_t *buf,
+ size_t size)
+{
+ if (!file->f_op->get_hash)
+ return -EOPNOTSUPP;
+
+ return file->f_op->get_hash(file, hash, buf, size);
+}
+EXPORT_SYMBOL(vfs_get_hash);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6c0b4a1c22ff..540316cfd461 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -40,6 +40,7 @@
#include <asm/byteorder.h>
#include <uapi/linux/fs.h>
+#include <uapi/linux/hash_info.h>
struct backing_dev_info;
struct bdi_writeback;
@@ -1764,6 +1765,8 @@ struct file_operations {
int (*dedupe_file_range)(struct file *, loff_t, struct file *, loff_t,
u64);
int (*fadvise)(struct file *, loff_t, loff_t, int);
+ int (*get_hash)(struct file *, enum hash_algo hash, uint8_t *buf,
+ size_t size);
} __randomize_layout;
struct inode_operations {
@@ -1838,7 +1841,8 @@ extern int vfs_dedupe_file_range(struct file *file,
extern int vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,
struct file *dst_file, loff_t dst_pos,
u64 len);
-
+extern int vfs_get_hash(struct file *file, enum hash_algo hash, uint8_t *buf,
+ size_t size);
struct super_operations {
struct inode *(*alloc_inode)(struct super_block *sb);
--
2.19.0.605.g01d371f741-goog
