From: Andreas Dilger Subject: Re: [PATCH 06/16] ext4: Calculate and verify inode checksums Date: Wed, 31 Aug 2011 20:30:25 -0600 Message-ID: References: <20110901003030.31048.99467.stgit@elm3c44.beaverton.ibm.com> <20110901003112.31048.36302.stgit@elm3c44.beaverton.ibm.com> Mime-Version: 1.0 (Apple Message framework v1084) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT Cc: Theodore Tso , Sunil Mushran , Amir Goldstein , linux-kernel , Andi Kleen , Mingming Cao , Joel Becker , linux-fsdevel , linux-ext4@vger.kernel.org, Coly Li To: "Darrick J. Wong" Return-path: Received: from idcmail-mo1so.shaw.ca ([24.71.223.10]:8890 "EHLO idcmail-mo1so.shaw.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757388Ab1IACa1 convert rfc822-to-8bit (ORCPT ); Wed, 31 Aug 2011 22:30:27 -0400 In-Reply-To: <20110901003112.31048.36302.stgit@elm3c44.beaverton.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 2011-08-31, at 6:31 PM, Darrick J. Wong wrote: > 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 > --- > 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 > #include > #include > +#include > > #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. > + __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. > + 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. > + 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 > + 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. > + 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