The goal of the salt is to prevent rainbow table attacks on users'
passphrases. The salt is fetched by e4crypto using an ioctl
interface; if the salt field in the superblock is not yet set, the
ioctl will generate a random UUID and use that as the salt for the
file system.
Change-Id: Icb8c901fb842eecd730f1bb3ef112e6607d77889
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
---
fs/ext4/ext4.h | 4 +++-
fs/ext4/ioctl.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 52 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index de3b1e4..0b281aa 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -612,6 +612,7 @@ enum {
#define EXT4_IOC_SWAP_BOOT _IO('f', 17)
#define EXT4_IOC_PRECACHE_EXTENTS _IO('f', 18)
#define EXT4_IOC_ENCRYPTION_POLICY _IOW('f', 19, struct ext4_encryption_policy)
+#define EXT4_IOC_GET_ENCRYPTION_PWSALT _IOW('f', 20, __u8[16])
#if defined(__KERNEL__) && defined(CONFIG_COMPAT)
/*
@@ -1172,7 +1173,8 @@ struct ext4_super_block {
__le32 s_overhead_clusters; /* overhead blocks/clusters in fs */
__le32 s_backup_bgs[2]; /* groups with sparse_super2 SBs */
__u8 s_encrypt_algos[4]; /* Encryption algorithms in use */
- __le32 s_reserved[105]; /* Padding to the end of the block */
+ __u8 s_encrypt_pw_salt[16]; /* Salt used for string2key algorithm */
+ __le32 s_reserved[101]; /* Padding to the end of the block */
__le32 s_checksum; /* crc32c(superblock) */
};
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index e4ae8f9..f5d8ec0 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -14,6 +14,7 @@
#include <linux/compat.h>
#include <linux/mount.h>
#include <linux/file.h>
+#include <linux/random.h>
#include <asm/uaccess.h>
#include "ext4_jbd2.h"
#include "ext4.h"
@@ -196,6 +197,16 @@ journal_err_out:
return err;
}
+static int uuid_is_zero(__u8 u[16])
+{
+ int i;
+
+ for (i=0; i < 16; i++)
+ if (u[i])
+ return 0;
+ return 1;
+}
+
long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
struct inode *inode = file_inode(filp);
@@ -635,6 +646,43 @@ encryption_policy_out:
#else
return -EOPNOTSUPP;
#endif
+ case EXT4_IOC_GET_ENCRYPTION_PWSALT:
+ {
+ int err, err2;
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+ handle_t *handle;
+
+ if (!ext4_sb_has_crypto(sb))
+ return -EOPNOTSUPP;
+ if (uuid_is_zero(sbi->s_es->s_encrypt_pw_salt)) {
+ err = mnt_want_write_file(filp);
+ if (err)
+ return err;
+ handle = ext4_journal_start_sb(sb, EXT4_HT_MISC, 1);
+ if (IS_ERR(handle)) {
+ err = PTR_ERR(handle);
+ goto pwsalt_err_exit;
+ }
+ err = ext4_journal_get_write_access(handle, sbi->s_sbh);
+ if (err)
+ goto pwsalt_err_journal;
+ generate_random_uuid(sbi->s_es->s_encrypt_pw_salt);
+ err = ext4_handle_dirty_metadata(handle, NULL,
+ sbi->s_sbh);
+ pwsalt_err_journal:
+ err2 = ext4_journal_stop(handle);
+ if (err2 && !err)
+ err = err2;
+ pwsalt_err_exit:
+ mnt_drop_write_file(filp);
+ if (err)
+ return err;
+ }
+ if (copy_to_user((void *) arg, sbi->s_es->s_encrypt_pw_salt,
+ 16))
+ return -EFAULT;
+ return 0;
+ }
default:
return -ENOTTY;
}
@@ -700,6 +748,7 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
case EXT4_IOC_RESIZE_FS:
case EXT4_IOC_PRECACHE_EXTENTS:
case EXT4_IOC_ENCRYPTION_POLICY:
+ case EXT4_IOC_GET_ENCRYPTION_PWSALT:
break;
default:
return -ENOIOCTLCMD;
--
2.3.0
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
