erofs: support superblock checksum

Introduce superblock checksum feature in order to
check at mounting time.

Note that the first 1024 bytes are ignore for x86
boot sectors and other oddities.

Link: https://lore.kernel.org/r/20191104024937.113939-1-gaoxiang25@huawei.com
Signed-off-by: Pratik Shinde <pratikshinde320@gmail.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>

diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
index 9d634d3a18451e1c8069e16a0a305c6b9f2ccf3d..74b0aaa7114c238788d9e78ad9a0c9439b368f79 100644 (file)
--- 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 b1ee5654750d8bbdcab42b6afc6ab10a9bf0518e..385fa49c7749fd7897fe91f13ab9c7823dabb714 100644 (file)
--- 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.
@@ -37,7 +39,6 @@ struct erofs_super_block {
        __u8 uuid[16];          /* 128-bit uuid for volume */
        __u8 volume_name[16];   /* volume name */
        __le32 feature_incompat;
-
        __u8 reserved2[44];
 };
 

diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 0c1175a08e54c8c81e37294fe07ddf5fc20b7437..6864fa4893e9661cadb263a53101266d84bda7d9 100644 (file)
--- 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;

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 0e369494f2f2c43601e9d8b97c285258db1877aa..849c0bdf49d9612538e1bb24b798e59794d43f3c 100644 (file)
--- 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 +47,30 @@ 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, crc;
+
+       dsb = kmemdup(sbdata + EROFS_SUPER_OFFSET,
+                     EROFS_BLKSIZ - EROFS_SUPER_OFFSET, GFP_KERNEL);
+       if (!dsb)
+               return -ENOMEM;
+
+       expected_crc = le32_to_cpu(dsb->checksum);
+       dsb->checksum = 0;
+       /* to allow for x86 boot sectors and other oddities. */
+       crc = crc32c(~0, dsb, EROFS_BLKSIZ - EROFS_SUPER_OFFSET);
+       kfree(dsb);
+
+       if (crc != expected_crc) {
+               erofs_err(sb, "invalid checksum 0x%08x, 0x%08x expected",
+                         crc, expected_crc);
+               return -EBADMSG;
+       }
+       return 0;
+}
+
 static void erofs_inode_init_once(void *ptr)
 {
        struct erofs_inode *vi = ptr;
@@ -112,7 +137,7 @@ 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 +146,13 @@ 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 +187,7 @@ static int erofs_read_superblock(struct super_block *sb)
        }
        ret = 0;
 out:
-       kunmap_atomic(data);
+       kunmap(page);
        put_page(page);
        return ret;
 }