RFR: 8329995: Restricted access to `/proc` can cause JFR initialization to crash

[David Holmes]

On Sun, 14 Apr 2024 08:53:05 GMT, Jaroslav Bachorik <jbachorik at openjdk.org> wrote:

> Please, review this trivial change to make using `ProcessIterator` more robust in the presence of SELinux or a similar system.
> 
> The call to `os::opendir("/proc")` may return `nulltptr` if the `/proc` is not accessible due to restrictions placed by the SELinux. In that case the `ProcessIterator` will SIGSEG because it assumes the `_dir`, which is the variable storing the result  of the `os::opendir("/proc")` call to be non-null.
> 
> The patch is missing regression test because it is very hard to simulate `/proc` not being accessible to the test process.

This change doesn't seem sufficient as many of the ProcessIterator functions access something under /proc without checking is_valid. Is it just  direct access to /proc that fails rather than specific entries?

src/hotspot/os/linux/os_perf_linux.cpp line 851:

> 849:   _entry = nullptr;
> 850:   _valid = _dir != nullptr;
> 851:   next_process();

A comment on the opendir would be useful e.g.

 _dir = os::opendir("/proc");  // May be null if /proc is not accessible.

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PR Review: https://git.openjdk.org/jdk/pull/18775#pullrequestreview-2000373079
PR Review Comment: https://git.openjdk.org/jdk/pull/18775#discussion_r1565398444