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 disk size, and trigger a BUG in ext4_ind_remove_space() [3]. According to the comment doc in ext4_ind_remove_space() the 'end' block parameter needs to be one block after the last block to remove. In the case when the BUG is triggered it points to the last block on a 4GB virtual disk image. This is calculated in ext4_ind_remove_space() in [4]. This patch adds a check that ensure the length + offest to be within the valid range and returns -ENOSPC error code in case it is invalid. LINK: [1] https://syzkaller.appspot.com/bug?id=b80bd9cf348aac724a4f4dff251800106d721331 LINK: [2] https://syzkaller.appspot.com/text?tag=ReproC&x=14ba0238700000 LINK: [3] https://elixir.bootlin.com/linux/v5.17-rc8/source/fs/ext4/indirect.c#L1244 LINK: [4] https://elixir.bootlin.com/linux/v5.17-rc8/source/fs/ext4/indirect.c#L1234 Cc: Theodore Ts'o <tytso@xxxxxxx> Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx> Cc: Ritesh Harjani <riteshh@xxxxxxxxxxxxx> Cc: <linux-ext4@xxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Cc: <linux-kernel@xxxxxxxxxxxxxxx> Fixes: a4bb6b64e39a ("ext4: enable "punch hole" functionality") Reported-by: syzbot+7a806094edd5d07ba029@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Tadeusz Struk <tadeusz.struk@xxxxxxxxxx> -- v2: Change sbi->s_blocksize to inode->i_sb->s_blocksize in maxlength computation. --- fs/ext4/inode.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) 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
