Re: [PATCH 06/16] ext4: Calculate and verify inode checksums
From: Andreas Dilger <adilger.kernel@dilger.ca>
Date: 2011-09-01 02:30:25
Also in:
linux-fsdevel, lkml
On 2011-08-31, at 6:31 PM, Darrick J. Wong wrote:
quoted hunk ↗ jump to hunk
This patch introduces to ext4 the ability to calculate and verify inode checksums. This requires the use of a new ro compatibility flag and some accompanying e2fsprogs patches to provide the relevant features in tune2fs and e2fsck. Signed-off-by: Darrick J. Wong <redacted> --- fs/ext4/ext4.h | 4 ++-- fs/ext4/inode.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 64 insertions(+), 2 deletions(-)diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index f79ddac..e2361cc 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h@@ -609,7 +609,7 @@ struct ext4_inode {__le16 l_i_file_acl_high; __le16 l_i_uid_high; /* these 2 fields */ __le16 l_i_gid_high; /* were reserved2[0] */ - __u32 l_i_reserved2; + __le32 l_i_checksum; /* crc32c(uuid+inum+inode) */ } linux2; struct { __le16 h_i_reserved1; /* Obsoleted fragment number/size which are removed in ext4 */@@ -727,7 +727,7 @@ do { \#define i_gid_low i_gid #define i_uid_high osd2.linux2.l_i_uid_high #define i_gid_high osd2.linux2.l_i_gid_high -#define i_reserved2 osd2.linux2.l_i_reserved2 +#define i_checksum osd2.linux2.l_i_checksum #elif defined(__GNU__)diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index c4da98a..44a7f88 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c@@ -38,6 +38,7 @@#include <linux/printk.h> #include <linux/slab.h> #include <linux/ratelimit.h> +#include <linux/crc32c.h> #include "ext4_jbd2.h" #include "xattr.h"@@ -49,6 +50,53 @@#define MPAGE_DA_EXTENT_TAIL 0x01 +static __le32 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw) +{ + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); + struct ext4_inode_info *ei = EXT4_I(inode); + int offset = offsetof(struct ext4_inode, i_checksum);
This could be declared "const int" so that it is not consuming space on the stack, or just put it inline in the code instead of a stack variable since it is a compile time constant.
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+ __le32 inum = cpu_to_le32(inode->i_ino); + __u32 crc = 0; + + if (EXT4_SB(inode->i_sb)->s_es->s_creator_os != + cpu_to_le32(EXT4_OS_LINUX))
This can be marked unlikely() I think.
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+ return 0; + if (!EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb, + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) + return 0; + + crc = crc32c_le(~0, sbi->s_es->s_uuid, sizeof(sbi->s_es->s_uuid)); + crc = crc32c_le(crc, (__u8 *)&inum, sizeof(inum));
I wonder if it makes sense to pre-compute the crc32c of s_uuid (stored in sbi) and/or s_uuid+inum (stored in struct ext4_inode_info). I suspect precomputing the s_uuid checksum is worthwhile, but I'm not sure whether precomputing the inode checksum is worthwhile unless it doesn't reduce the number of ext4_inode_info structs per page in the slab.
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+ crc = crc32c_le(crc, (__u8 *)raw, offset); + offset += sizeof(raw->i_checksum); /* skip checksum */ + crc = crc32c_le(crc, (__u8 *)raw + offset, + EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize - + offset);
I suspect it would be more efficient to set raw->i_checksum = 0, then compute the checksum on the whole raw inode buffer, and fill in raw->i_checksum = cpu_to_le32(crc) at the end. That would mean the caller ext4_inode_csum_verify() should save the original checksum for comparison with the returned value. The one problem with this is that it is racy w.r.t other users
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+ return cpu_to_le32(crc); +} + +static int ext4_inode_csum_verify(struct inode *inode, struct ext4_inode *raw) +{ + if (EXT4_SB(inode->i_sb)->s_es->s_creator_os == + cpu_to_le32(EXT4_OS_LINUX) && + EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb, + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM) && + (raw->i_checksum != ext4_inode_csum(inode, raw)))
This check can be marked unlikely(), since the rare case of a checksum failure can cause a stall in the execution pipeline. It might make sense to put the unlikely() at the lone callsite to move the whole function call overhead out-of-line.
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+ return 0; + return 1; +} + +static void ext4_inode_csum_set(struct inode *inode, struct ext4_inode *raw) +{ + if (EXT4_SB(inode->i_sb)->s_es->s_creator_os != + cpu_to_le32(EXT4_OS_LINUX) || + !EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb, + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) + return; + + raw->i_checksum = ext4_inode_csum(inode, raw); +} + static inline int ext4_begin_ordered_truncate(struct inode *inode, loff_t new_size) {@@ -3410,6 +3458,15 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)if (ret < 0) goto bad_inode; raw_inode = ext4_raw_inode(&iloc); + + if (!ext4_inode_csum_verify(inode, raw_inode)) { + EXT4_ERROR_INODE(inode, "checksum invalid (0x%x != 0x%x)", + le32_to_cpu(ext4_inode_csum(inode, raw_inode)), + le32_to_cpu(raw_inode->i_checksum)); + ret = -EIO; + goto bad_inode; + } + inode->i_mode = le16_to_cpu(raw_inode->i_mode); inode->i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low); inode->i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);@@ -3490,6 +3547,9 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize); if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize > EXT4_INODE_SIZE(inode->i_sb)) { + EXT4_ERROR_INODE(inode, "bad extra_isize (%u != %u)", + EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize, + EXT4_INODE_SIZE(inode->i_sb)); ret = -EIO; goto bad_inode; }@@ -3731,6 +3791,8 @@ static int ext4_do_update_inode(handle_t *handle,raw_inode->i_extra_isize = cpu_to_le16(ei->i_extra_isize); } + ext4_inode_csum_set(inode, raw_inode);
This might warrant a comment to always be the last function before submitting the inode to the journal.
BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata"); rc = ext4_handle_dirty_metadata(handle, NULL, bh); if (!err)
Also, rather than just making the checksum be updated at commit time, it makes more sense to have ext4_do_update_inode() only be called once per commit, since this is an expensive function. Cheers, Andreas