Linux-EROFS Archive on lore.kernel.org
 help / color / Atom feed
From: Chao Yu <yuchao0@huawei.com>
To: Gao Xiang <gaoxiang25@huawei.com>, Chao Yu <chao@kernel.org>,
	<linux-erofs@lists.ozlabs.org>
Cc: Gao Xiang <xiang@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] erofs: support superblock checksum
Date: Wed, 23 Oct 2019 16:15:29 +0800
Message-ID: <f158affb-c5c5-9cbe-d87d-17210bc635fe@huawei.com> (raw)
In-Reply-To: <20191023040557.230886-1-gaoxiang25@huawei.com>

Hi, Xiang, Pratik,

On 2019/10/23 12:05, Gao Xiang wrote:
> From: Pratik Shinde <pratikshinde320@gmail.com>
> 
> Introduce superblock checksum feature in order to check
> a number of given blocks at mounting time.
> 
> Signed-off-by: Pratik Shinde <pratikshinde320@gmail.com>
> Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
> ---
> changes from v3:
>  (based on Pratik's v3 patch)
>  - add LIBCRC32C dependency;
>  - use kmap() in order to avoid sleeping in atomic context;
>  - skip the first 1024 byte for x86 boot sector,
>    co-tested with userspace utils,
>    https://lore.kernel.org/r/20191023034957.184711-1-gaoxiang25@huawei.com
> 
>  fs/erofs/Kconfig    |  1 +
>  fs/erofs/erofs_fs.h |  6 +++--
>  fs/erofs/internal.h |  2 ++
>  fs/erofs/super.c    | 53 +++++++++++++++++++++++++++++++++++++++++++--
>  4 files changed, 58 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
> index 9d634d3a1845..74b0aaa7114c 100644
> --- a/fs/erofs/Kconfig
> +++ b/fs/erofs/Kconfig
> @@ -3,6 +3,7 @@
>  config EROFS_FS
>  	tristate "EROFS filesystem support"
>  	depends on BLOCK
> +	select LIBCRC32C
>  	help
>  	  EROFS (Enhanced Read-Only File System) is a lightweight
>  	  read-only file system with modern designs (eg. page-sized
> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> index b1ee5654750d..461913be1d1c 100644
> --- a/fs/erofs/erofs_fs.h
> +++ b/fs/erofs/erofs_fs.h
> @@ -11,6 +11,8 @@
>  
>  #define EROFS_SUPER_OFFSET      1024
>  
> +#define EROFS_FEATURE_COMPAT_SB_CHKSUM          0x00000001
> +
>  /*
>   * Any bits that aren't in EROFS_ALL_FEATURE_INCOMPAT should
>   * be incompatible with this kernel version.
> @@ -37,8 +39,8 @@ struct erofs_super_block {
>  	__u8 uuid[16];          /* 128-bit uuid for volume */
>  	__u8 volume_name[16];   /* volume name */
>  	__le32 feature_incompat;
> -
> -	__u8 reserved2[44];
> +	__le32 chksum_blocks;	/* number of blocks used for checksum */
> +	__u8 reserved2[40];
>  };
>  
>  /*
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 544a453f3076..a3778f597bf6 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -85,6 +85,7 @@ struct erofs_sb_info {
>  
>  	u8 uuid[16];                    /* 128-bit uuid for volume */
>  	u8 volume_name[16];             /* volume name */
> +	u32 feature_compat;
>  	u32 feature_incompat;
>  
>  	unsigned int mount_opt;
> @@ -426,6 +427,7 @@ static inline void z_erofs_exit_zip_subsystem(void) {}
>  #endif	/* !CONFIG_EROFS_FS_ZIP */
>  
>  #define EFSCORRUPTED    EUCLEAN         /* Filesystem is corrupted */
> +#define EFSBADCRC       EBADMSG         /* Bad CRC detected */
>  
>  #endif	/* __EROFS_INTERNAL_H */
>  
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 0e369494f2f2..18d1ec18a671 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -9,6 +9,7 @@
>  #include <linux/statfs.h>
>  #include <linux/parser.h>
>  #include <linux/seq_file.h>
> +#include <linux/crc32c.h>
>  #include "xattr.h"
>  
>  #define CREATE_TRACE_POINTS
> @@ -46,6 +47,47 @@ void _erofs_info(struct super_block *sb, const char *function,
>  	va_end(args);
>  }
>  
> +static int erofs_superblock_csum_verify(struct super_block *sb, void *sbdata)
> +{
> +	struct erofs_super_block *dsb;
> +	u32 expected_crc, nblocks, crc;
> +	void *kaddr;
> +	struct page *page;
> +	int i;
> +
> +	dsb = kmemdup(sbdata + EROFS_SUPER_OFFSET,
> +		      EROFS_BLKSIZ - EROFS_SUPER_OFFSET, GFP_KERNEL);
> +	if (!dsb)
> +		return -ENOMEM;
> +
> +	expected_crc = le32_to_cpu(dsb->checksum);
> +	nblocks = le32_to_cpu(dsb->chksum_blocks);

Now, we try to use nblocks's value before checking its validation, I guess fuzz
test can easily make the value extreme larger, result in checking latter blocks
unnecessarily.

IMO, we'd better
1. check validation of superblock to make sure all fields in sb are valid
2. use .nblocks to count and check payload blocks following sb

Thanks,

> +	dsb->checksum = 0;
> +	/* to allow for x86 boot sectors and other oddities. */
> +	crc = crc32c(~0, dsb, EROFS_BLKSIZ - EROFS_SUPER_OFFSET);
> +	kfree(dsb);
> +
> +	for (i = 1; i < nblocks; i++) {
> +		page = erofs_get_meta_page(sb, i);
> +		if (IS_ERR(page))
> +			return PTR_ERR(page);
> +
> +		kaddr = kmap_atomic(page);
> +		crc = crc32c(crc, kaddr, EROFS_BLKSIZ);
> +		kunmap_atomic(kaddr);
> +
> +		unlock_page(page);
> +		put_page(page);
> +	}
> +
> +	if (crc != expected_crc) {
> +		erofs_err(sb, "invalid checksum 0x%08x, 0x%08x expected",
> +			  crc, expected_crc);
> +		return -EFSBADCRC;
> +	}
> +	return 0;
> +}
> +
>  static void erofs_inode_init_once(void *ptr)
>  {
>  	struct erofs_inode *vi = ptr;
> @@ -112,7 +154,7 @@ static int erofs_read_superblock(struct super_block *sb)
>  
>  	sbi = EROFS_SB(sb);
>  
> -	data = kmap_atomic(page);
> +	data = kmap(page);
>  	dsb = (struct erofs_super_block *)(data + EROFS_SUPER_OFFSET);
>  
>  	ret = -EINVAL;
> @@ -121,6 +163,13 @@ static int erofs_read_superblock(struct super_block *sb)
>  		goto out;
>  	}
>  
> +	sbi->feature_compat = le32_to_cpu(dsb->feature_compat);
> +	if (sbi->feature_compat & EROFS_FEATURE_COMPAT_SB_CHKSUM) {
> +		ret = erofs_superblock_csum_verify(sb, data);
> +		if (ret)
> +			goto out;
> +	}
> +
>  	blkszbits = dsb->blkszbits;
>  	/* 9(512 bytes) + LOG_SECTORS_PER_BLOCK == LOG_BLOCK_SIZE */
>  	if (blkszbits != LOG_BLOCK_SIZE) {
> @@ -155,7 +204,7 @@ static int erofs_read_superblock(struct super_block *sb)
>  	}
>  	ret = 0;
>  out:
> -	kunmap_atomic(data);
> +	kunmap(data);
>  	put_page(page);
>  	return ret;
>  }
> 

  reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-22 18:06 [PATCH-v3] erofs: code for verifying superblock checksum of an erofs image Pratik Shinde
2019-10-23  4:05 ` [PATCH v4] erofs: support superblock checksum Gao Xiang
2019-10-23  8:15   ` Chao Yu [this message]
2019-10-23  8:45     ` Gao Xiang
2019-10-28 12:36       ` Chao Yu
2019-10-28 13:44         ` Gao Xiang
2019-10-28 14:32           ` [PATCH v5] " Gao Xiang
2019-10-30  2:33             ` Chao Yu
2019-10-30  2:56               ` Gao Xiang
2019-10-30  5:08                 ` [PATCH v6] " Gao Xiang
2019-11-04  2:49                   ` [PATCH v7] " Gao Xiang

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=f158affb-c5c5-9cbe-d87d-17210bc635fe@huawei.com \
    --to=yuchao0@huawei.com \
    --cc=chao@kernel.org \
    --cc=gaoxiang25@huawei.com \
    --cc=linux-erofs@lists.ozlabs.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=xiang@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-EROFS Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-erofs/0 linux-erofs/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-erofs linux-erofs/ https://lore.kernel.org/linux-erofs \
		linux-erofs@lists.ozlabs.org linux-erofs@ozlabs.org
	public-inbox-index linux-erofs

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.ozlabs.lists.linux-erofs


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git