[PATCH 4.9 21/24] ext4: limit length to bitmap_maxbytes - blocksize in punch_hole

[Greg Kroah-Hartman]

From: Tadeusz Struk <tadeusz.struk@xxxxxxxxxx>

commit 2da376228a2427501feb9d15815a45dbdbdd753e upstream.

Syzbot found an issue [1] in ext4_fallocate().
The C reproducer [2] calls fallocate(), passing size 0xffeffeff000ul,
and offset 0x1000000ul, which, when added together exceed the
bitmap_maxbytes for the inode. This triggers a BUG in
ext4_ind_remove_space(). According to the comments in this function
the 'end' parameter needs to be one block after the last block to be
removed. In the case when the BUG is triggered it points to the last
block. Modify the ext4_punch_hole() function and add constraint that
caps the length to satisfy the one before laster block requirement.

LINK: [1] https://syzkaller.appspot.com/bug?id=b80bd9cf348aac724a4f4dff251800106d721331
LINK: [2] https://syzkaller.appspot.com/text?tag=ReproC&x=14ba0238700000

Fixes: a4bb6b64e39a ("ext4: enable "punch hole" functionality")
Reported-by: syzbot+7a806094edd5d07ba029@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Tadeusz Struk <tadeusz.struk@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220331200515.153214-1-tadeusz.struk@xxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Cc: stable@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/ext4/inode.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3980,7 +3980,8 @@ int ext4_punch_hole(struct inode *inode,
 	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;
@@ -4026,6 +4027,14 @@ int ext4_punch_hole(struct inode *inode,
 		   offset;
 	}
 
+	/*
+	 * For punch hole the length + offset needs to be within one block
+	 * before last range. Adjust the length if it goes beyond that limit.
+	 */
+	max_length = sbi->s_bitmap_maxbytes - inode->i_sb->s_blocksize;
+	if (offset + length > max_length)
+		length = max_length - offset;
+
 	if (offset & (sb->s_blocksize - 1) ||
 	    (offset + length) & (sb->s_blocksize - 1)) {
 		/*