ext4: store checksum seed in superblock

Allow the filesystem to store the metadata checksum seed in the
superblock and add an incompat feature to say that we're using it.
This enables tune2fs to change the UUID on a mounted metadata_csum
FS without having to (racy!) rewrite all disk metadata.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
(cherry picked from commit 8c81bd8f586c46eaf114758a78d82895a2b081c2)

Orabug: 25802481
CVE-2016-10208

Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>
 Conflicts:
	fs/ext4/sysfs.c

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 23b6523a705a95a97abdcecbb3171c106f1b746e..0db69ab59cdf2f07094943cd3f19b4cef86c17be 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1221,7 +1221,8 @@ struct ext4_super_block {
        __u8    s_encrypt_pw_salt[16];  /* Salt used for string2key algorithm */
        __le32  s_lpf_ino;              /* Location of the lost+found inode */
        __le32  s_prj_quota_inum;       /* inode for tracking project quota */
-       __le32  s_reserved[99];         /* Padding to the end of the block */
+       __le32  s_checksum_seed;        /* crc32c(uuid) if csum_seed set */
+       __le32  s_reserved[98];         /* Padding to the end of the block */
        __le32  s_checksum;             /* crc32c(superblock) */
 };
 
@@ -1619,7 +1620,7 @@ static inline int ext4_encrypted_inode(struct inode *inode)
 #define EXT4_FEATURE_INCOMPAT_FLEX_BG          0x0200
 #define EXT4_FEATURE_INCOMPAT_EA_INODE         0x0400 /* EA in inode */
 #define EXT4_FEATURE_INCOMPAT_DIRDATA          0x1000 /* data in dirent */
-#define EXT4_FEATURE_INCOMPAT_BG_USE_META_CSUM 0x2000 /* use crc32c for bg */
+#define EXT4_FEATURE_INCOMPAT_CSUM_SEED                0x2000
 #define EXT4_FEATURE_INCOMPAT_LARGEDIR         0x4000 /* >2GB or 3-lvl htree */
 #define EXT4_FEATURE_INCOMPAT_INLINE_DATA      0x8000 /* data in inode */
 #define EXT4_FEATURE_INCOMPAT_ENCRYPT          0x10000
@@ -1736,7 +1737,8 @@ EXT4_FEATURE_INCOMPAT_FUNCS(encrypt,              ENCRYPT)
                                         EXT4_FEATURE_INCOMPAT_FLEX_BG| \
                                         EXT4_FEATURE_INCOMPAT_MMP | \
                                         EXT4_FEATURE_INCOMPAT_INLINE_DATA | \
-                                        EXT4_FEATURE_INCOMPAT_ENCRYPT)
+                                        EXT4_FEATURE_INCOMPAT_ENCRYPT | \
+                                        EXT4_FEATURE_INCOMPAT_CSUM_SEED)
 #define EXT4_FEATURE_RO_COMPAT_SUPP    (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
                                         EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
                                         EXT4_FEATURE_RO_COMPAT_GDT_CSUM| \

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 26b88c0bc6f799332326126f9fe1e2517af36661..60097f0a12497c6257fc01f59a879d4359e65efc 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3559,7 +3559,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
        }
 
        /* Precompute checksum seed for all metadata */
-       if (ext4_has_metadata_csum(sb))
+       if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_CSUM_SEED))
+               sbi->s_csum_seed = le32_to_cpu(es->s_checksum_seed);
+       else if (ext4_has_metadata_csum(sb))
                sbi->s_csum_seed = ext4_chksum(sbi, ~0, es->s_uuid,
                                               sizeof(es->s_uuid));