[PATCH] ext2: strengthen value length check in ext2_xattr_set()

[Chengguang Xu <cgxu519@zoho.com.cn>]

Actually maximum length of a valid entry value is not
->s_blocksize because header, last entry and entry
name will also occupy some spaces. This patch
strengthens the value length check and return -ERANGE
when the length is larger than allowed maximum length.

Signed-off-by: Chengguang Xu <cgxu519@zoho.com.cn>
---
 fs/ext2/xattr.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
index f1f857b83b45..425c8e29d3cb 100644
--- a/fs/ext2/xattr.c
+++ b/fs/ext2/xattr.c
@@ -399,7 +399,7 @@ ext2_xattr_set(struct inode *inode, int name_index, const char *name,
 	struct buffer_head *bh = NULL;
 	struct ext2_xattr_header *header = NULL;
 	struct ext2_xattr_entry *here, *last;
-	size_t name_len, free, min_offs = sb->s_blocksize;
+	size_t name_len, free, min_offs = sb->s_blocksize, max_len;
 	int not_found = 1, error;
 	char *end;
 	
@@ -423,7 +423,10 @@ ext2_xattr_set(struct inode *inode, int name_index, const char *name,
 	if (name == NULL)
 		return -EINVAL;
 	name_len = strlen(name);
-	if (name_len > 255 || value_len > sb->s_blocksize)
+	max_len = sb->s_blocksize - sizeof(struct ext2_xattr_header)
+			- sizeof(__u32);
+	if (name_len > 255 ||
+	    EXT2_XATTR_LEN(name_len) + EXT2_XATTR_SIZE(value_len) > max_len)
 		return -ERANGE;
 	down_write(&EXT2_I(inode)->xattr_sem);
 	if (EXT2_I(inode)->i_file_acl) {
-- 
2.20.1