[PATCH v2] ext4: check if offset+length is within valid fallocate

[Tadeusz Struk <tadeusz.struk@linaro.org>]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

==============================================
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 01c9e4f743ba..355384007d11 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3924,7 +3924,8 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
 	struct super_block *sb = inode->i_sb;
 	ext4_lblk_t first_block, stop_block;
 	struct address_space *mapping = inode->i_mapping;
-	loff_t first_block_offset, last_block_offset;
+	loff_t first_block_offset, last_block_offset, max_length;
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 	handle_t *handle;
 	unsigned int credits;
 	int ret = 0, ret2 = 0;
@@ -3967,6 +3968,16 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
 		   offset;
 	}
 
+	/*
+	 * For punch hole the length + offset needs to be at least within
+	 * one block before last
+	 */
+	max_length = sbi->s_bitmap_maxbytes - inode->i_sb->s_blocksize;
+	if (offset + length >= max_length) {
+		ret = -ENOSPC;
+		goto out_mutex;
+	}
+
 	if (offset & (sb->s_blocksize - 1) ||
 	    (offset + length) & (sb->s_blocksize - 1)) {
 		/*
-- 
2.35.1