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Prevent subtract with overflow

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This changes assumes this only happens when the archive is invalid.

Fixes #40
This commit is contained in:
Pascal Hertleif 2017-06-27 11:23:17 +02:00
parent 5c12e511d1
commit 57a6514a40
1 changed files with 3 additions and 1 deletions
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4
src/read.rs
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@ -85,7 +85,9 @@ impl<R: Read+io::Seek> ZipArchive<R>
// Some zip files have data prepended to them, resulting in the offsets all being too small. Get the amount of // Some zip files have data prepended to them, resulting in the offsets all being too small. Get the amount of
// error by comparing the actual file position we found the CDE at with the offset recorded in the CDE. // error by comparing the actual file position we found the CDE at with the offset recorded in the CDE.
let archive_offset = cde_start_pos - footer.central_directory_size - footer.central_directory_offset; let archive_offset = cde_start_pos.checked_sub(footer.central_directory_size)
.and_then(|x| x.checked_sub(footer.central_directory_offset))
.ok_or(ZipError::InvalidArchive("Invalid central directory size or offset"))?;
let directory_start = (footer.central_directory_offset + archive_offset) as u64; let directory_start = (footer.central_directory_offset + archive_offset) as u64;
let number_of_files = footer.number_of_files_on_this_disk as usize; let number_of_files = footer.number_of_files_on_this_disk as usize;