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Andrew Dunham ccace1f7df ssh/tailssh: fix privilege dropping on FreeBSD; add tests ... On FreeBSD and Darwin, changing a process's supplementary groups with setgroups(2) will also change the egid of the process, setting it to the first entry in the provided list. This is distinct from the behaviour on other platforms (and possibly a violation of the POSIX standard). Because of this, on FreeBSD with no TTY, our incubator code would previously not change the process's gid, because it would read the newly-changed egid, compare it against the expected egid, and since they matched, not change the gid. Because we didn't use the 'login' program on FreeBSD without a TTY, this would propagate to a child process. This could be observed by running "id -p" in two contexts. The expected output, and the output returned when running from a SSH shell, is: andrew@freebsd:~ $ id -p uid andrew groups andrew However, when run via "ssh andrew@freebsd id -p", the output would be: $ ssh andrew@freebsd id -p login root uid andrew rgid wheel groups andrew (this could also be observed via "id -g -r" to print just the gid) We fix this by pulling the details of privilege dropping out into their own function and prepending the expected gid to the start of the list on Darwin and FreeBSD. Finally, we add some tests that run a child process, drop privileges, and assert that the final UID/GID/additional groups are what we expect. More information can be found in the following article: https://www.usenix.org/system/files/login/articles/325-tsafrir.pdf Updates #7616 Alternative to #7609 Signed-off-by: Andrew Dunham <andrew@du.nham.ca> Change-Id: I0e6513c31b121108b50fe561c89e5816d84a45b9		2 years ago
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tailssh	ssh/tailssh: fix privilege dropping on FreeBSD; add tests	2 years ago