36 lines
1.5 KiB
Diff
36 lines
1.5 KiB
Diff
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From d9efc31daf2206f7d3fdb839863cf7a576a2eb57 Mon Sep 17 00:00:00 2001
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From: Aleksa Sarai <cyphar@cyphar.com>
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Date: Wed, 24 Mar 2021 00:17:06 +1100
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Subject: [PATCH] layer: don't permit / type to be changed on extraction
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If users can change the type of / to a symlink, they can cause umoci to
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overwrite host files. This is obviously bad, and is not caught by the
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rest of our directory escape detection code because the root itself has
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been changed to a different directory.
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Fixes: CVE-2021-29136
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Reported-by: Robin Peraglie <robin@cure53.de>
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Tested-by: Daniel Dao <dqminh89@gmail.com>
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Reviewed-by: Tycho Andersen <tycho@tycho.pizza>
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Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
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---
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oci/layer/tar_extract.go | 5 +++++
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1 file changed, 5 insertions(+)
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diff --git a/oci/layer/tar_extract.go b/oci/layer/tar_extract.go
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index 1b8c3d67..d7414105 100644
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--- a/oci/layer/tar_extract.go
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+++ b/oci/layer/tar_extract.go
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@@ -404,6 +404,11 @@ func (te *TarExtractor) UnpackEntry(root string, hdr *tar.Header, r io.Reader) (
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if filepath.Join("/", hdr.Name) == "/" {
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// If we got an entry for the root, then unsafeDir is the full path.
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unsafeDir, file = hdr.Name, "."
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+ // If we're being asked to change the root type, bail because they may
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+ // change it to a symlink which we could inadvertently follow.
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+ if hdr.Typeflag != tar.TypeDir {
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+ return errors.New("malicious tar entry -- refusing to change type of root directory")
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+ }
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}
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dir, err := securejoin.SecureJoinVFS(root, unsafeDir, te.fsEval)
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if err != nil {
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