Cap the amount of data util.Unzip extracts - #4207
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Unzip copied every archive entry with io.Copy and no bound on the output, so a small crafted archive handed to a plugin could expand until the disk filled. The function already rejects entries that escape the destination directory; this adds the matching check for size. Extraction now has a 1 GiB budget per archive. Each entry's declared uncompressed size is checked against what is left before anything is written, and the bytes actually written are subtracted afterwards. archive/zip refuses to read past the size declared in an entry's header, so the declared size is a real upper bound and no second limit is needed on the copy. Exceeding the budget returns an error in the same style as the traversal check. The new test for a plain archive also showed that Unzip created the parent directory of a file entry with the file's own mode. Archives without directory entries, such as ones written by Go's archive/zip, ended up with an unsearchable 0644 directory on Unix and every file inside it failed to open. Parent directories now get 0755, the same as the destination directory. Fixes micro-editor#4161
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| @@ -639,6 +642,8 @@ func Unzip(src, dest string) error { | |||
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| os.MkdirAll(dest, 0755) | |||
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Instead of 0755 I'm thinking about a DirMode analogue to:
Line 52 in 393cf24
This is then valid for the newly introduced 0755 in line 672 too as well as in:
micro/internal/config/plugin_installer.go
Line 423 in 393cf24
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Good idea, done in ff05d1a: a DirMode constant next to FileMode, used for both MkdirAll calls in Unzip and for dirPerm in the plugin installer.
Unzip and the plugin installer both created directories with a bare 0755, so give it a DirMode constant next to FileMode and use it in all three places.
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util.Unzipininternal/util/util.gocopies each archive entry withio.Copyand never checks how much it has written, so a plugin that unpacks a downloaded archive can expand a small zip bomb until the disk is full. The function already rejects entries whose path escapes the destination, but had no equivalent check on size.Each
Unzipcall now has a 1 GiB budget, and an entry whose declared uncompressed size does not fit fails withfile too large: <path>before anything is written; the declared size is trustworthy becausearchive/ziprefuses to read past it. Parent directories are now created with 0755 instead of the entry's file mode, which left them unenterable on Unix. New tests cover a normal archive, an overstated header and an understated one.Fixes #4161