staging: erofs: add requirements field in superblock

There are some backward incompatible features pending
for months, mainly due to on-disk format expensions.

However, we should ensure that it cannot be mounted with
old kernels. Otherwise, it will causes unexpected behaviors.

Fixes: ba2b77a82022 ("staging: erofs: add super block operations")
Cc: <stable@vger.kernel.org> # 4.19+
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/erofs/erofs_fs.h b/drivers/staging/erofs/erofs_fs.h
index fa52898df006e908955f64fc9793fe42755bd228..8ddb2b3e7d394513ca3acac4a2953390d576a5de 100644 (file)
--- a/drivers/staging/erofs/erofs_fs.h
+++ b/drivers/staging/erofs/erofs_fs.h
@@ -17,10 +17,16 @@
 #define EROFS_SUPER_MAGIC_V1    0xE0F5E1E2
 #define EROFS_SUPER_OFFSET      1024
 
+/*
+ * Any bits that aren't in EROFS_ALL_REQUIREMENTS should be
+ * incompatible with this kernel version.
+ */
+#define EROFS_ALL_REQUIREMENTS  0
+
 struct erofs_super_block {
 /*  0 */__le32 magic;           /* in the little endian */
 /*  4 */__le32 checksum;        /* crc32c(super_block) */
-/*  8 */__le32 features;
+/*  8 */__le32 features;        /* (aka. feature_compat) */
 /* 12 */__u8 blkszbits;         /* support block_size == PAGE_SIZE only */
 /* 13 */__u8 reserved;
 
@@ -34,9 +40,10 @@ struct erofs_super_block {
 /* 44 */__le32 xattr_blkaddr;
 /* 48 */__u8 uuid[16];          /* 128-bit uuid for volume */
 /* 64 */__u8 volume_name[16];   /* volume name */
+/* 80 */__le32 requirements;    /* (aka. feature_incompat) */
 
-/* 80 */__u8 reserved2[48];     /* 128 bytes */
-} __packed;
+/* 84 */__u8 reserved2[44];
+} __packed;                     /* 128 bytes */
 
 /*
  * erofs inode data mapping:

diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
index c47778b3fabd31a3648b285907b7ff1377b9dae2..382258fc124da1afabd1ba5bd9088a91a0bda216 100644 (file)
--- a/drivers/staging/erofs/internal.h
+++ b/drivers/staging/erofs/internal.h
@@ -115,6 +115,8 @@ struct erofs_sb_info {
 
        u8 uuid[16];                    /* 128-bit uuid for volume */
        u8 volume_name[16];             /* volume name */
+       u32 requirements;
+
        char *dev_name;
 
        unsigned int mount_opt;

diff --git a/drivers/staging/erofs/super.c b/drivers/staging/erofs/super.c
index f580d4ef77a1b94088e94920e03c00b82d7db803..cadbcc11702aa7a0eb5f914478e9eed5ad5e9351 100644 (file)
--- a/drivers/staging/erofs/super.c
+++ b/drivers/staging/erofs/super.c
@@ -71,6 +71,22 @@ static void free_inode(struct inode *inode)
        kmem_cache_free(erofs_inode_cachep, vi);
 }
 
+static bool check_layout_compatibility(struct super_block *sb,
+                                      struct erofs_super_block *layout)
+{
+       const unsigned int requirements = le32_to_cpu(layout->requirements);
+
+       EROFS_SB(sb)->requirements = requirements;
+
+       /* check if current kernel meets all mandatory requirements */
+       if (requirements & (~EROFS_ALL_REQUIREMENTS)) {
+               errln("unidentified requirements %x, please upgrade kernel version",
+                     requirements & ~EROFS_ALL_REQUIREMENTS);
+               return false;
+       }
+       return true;
+}
+
 static int superblock_read(struct super_block *sb)
 {
        struct erofs_sb_info *sbi;
@@ -104,6 +120,9 @@ static int superblock_read(struct super_block *sb)
                goto out;
        }
 
+       if (!check_layout_compatibility(sb, layout))
+               goto out;
+
        sbi->blocks = le32_to_cpu(layout->blocks);
        sbi->meta_blkaddr = le32_to_cpu(layout->meta_blkaddr);
 #ifdef CONFIG_EROFS_FS_XATTR