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=b80bd9cf348aac724a4f4dff251800106d72133... LINK: [2] https://syzkaller.appspot.com/text?tag=ReproC&x=14ba0238700000

Cc: Theodore Ts'o tytso@mit.edu Cc: Andreas Dilger adilger.kernel@dilger.ca Cc: Ritesh Harjani riteshh@linux.ibm.com Cc: linux-ext4@vger.kernel.org Cc: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org

Fixes: a4bb6b64e39a ("ext4: enable "punch hole" functionality") Reported-by: syzbot+7a806094edd5d07ba029@syzkaller.appspotmail.com Signed-off-by: Tadeusz Struk tadeusz.struk@linaro.org -- v3: Modify the length instead of returning an error. v2: Change sbi->s_blocksize to inode->i_sb->s_blocksize in maxlength computation. --- fs/ext4/inode.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 1ce13f69fbec..60bf31765d07 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -3958,7 +3958,8 @@ 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; @@ -4001,6 +4002,14 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length) 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)) { /*