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server: fix TOCTOU filesystem race condition #86

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server: fix TOCTOU filesystem race condition #86

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Commits on May 25, 2023

  1. server: fix TOCTOU filesystem race condition 

    CreateAuth() opens a file and then, if the opening was successful,
its permissions are changed with chmod.
However, an attacker might change the target of the file name between
the initial opening and the permissions change, potentially changing the
permissions of a different file.

This can be avoided by using fchmod with the file descriptor that was
received from opening the file. This ensures that the permissions change
is applied to the very same file that was opened.

Also, we need to close the file if open() succeeds but fchmod() fails.

Reference: CWE-367
    @szsam
    szsam committed May 25, 2023
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