Incus has Nil-Pointer Dereference via S3 Bucket Import

Summary

Missing error handling could lead an authenticated Incus user to cause a daemon crash through the import of a truncated storage bucket backup file.

Details

It was found that TransferManager.UploadAllFiles iterates over tar entries but only checks for io.EOF from tr.Next(). When tr.Next() returns a non-EOF error, such as unexpected EOF from a truncated archive, the header hdr is nil and the code continues to access hdr.Name, causing a nil-pointer dereference that panics the daemon.

This may allow the Incus daemon to be crashed during S3 bucket restore if a truncated or corrupted backup archive is provided. A panic can occur when a malformed archive produces a non-EOF tar read error after the first entry. Any caller of UploadAllFiles that processes attacker-controlled archive content may be affected.

Affected File: https://github.com/lxc/incus/blob/v6.22.0/…server/storage/s3/transfer_manager.go#L127

The tar-iteration loop only checks for EOF:

Affected Code:

for {
    hdr, err := tr.Next()
    if err == io.EOF {
        break // End of archive.
    }

    // Skip index.yaml file
    if hdr.Name == "backup/index.yaml" {

When tr.Next() returns a non-EOF error, hdr is nil. The code does not check for this case and immediately dereferences hdr.Name.

This was confirmed as follows:

Command:

go test ./test/fuzz -run='FuzzS3BucketUploadTarParsing/s3_nil_deref_truncated_tar' -count=1 -v

Output:

=== RUN   FuzzS3BucketUploadTarParsing
=== RUN   FuzzS3BucketUploadTarParsing/s3_nil_deref_truncated_tar
   s3_bucket_upload_fuzz_test.go:82: UploadAllFiles panicked: runtime error: invalid memory address
       or nil pointer dereference
--- FAIL: FuzzS3BucketUploadTarParsing/s3_nil_deref_truncated_tar (0.00s)
FAIL

It is recommended to add a non-EOF error check after tr.Next().

Proposed Fix:

hdr, err := tr.Next()
if err == io.EOF {
    break
}

if err != nil {
    return fmt.Errorf("Error reading backup archive: %w", err)
}

A patch is available at https://github.com/lxc/incus/releases/tag/v7.0.0.

Credits

This issue was discovered and reported by the team at 7asecurity (https://7asecurity.com/)