Increase stack size limit on Linux

[kevinbackhouse]

I'm not sure why I never thought of this solution before. We keep getting "security" reports like #9303 which trigger a crash by causing the process to run out of stack space due to a deep recursion. On Linux, the default stack size is 8192KB, which makes it very easy to hit the limit. I've never considered this to be a genuine security issue because it's trivial to increase the limit with a command like ulimit -s 10000000. But today, I realized that we can do that ourselves in the Exiv2 app, by calling setrlimit.

There are two limits: the "soft" limit and the "hard" limit. An unprivileged process like Exiv2 is allowed to increase its own soft limit (no higher than the hard limit). In this PR, I'm setting it as high as it will go. We could choose some other number like 1MB, but I can't see any particular benefit to that.

On Windows, the default size is apparently 1MB. I've never tested one of these issues on Windows, so I'm not sure if the behavior is the same as Linux. I'll do some investigation, but I expect Windows also has a way to increase the stack size.

Given that all of our parsing algorithms use recursion, I think that increasing the stack size limit is by far the easiest and best way to handle deeply nested files.

[Copilot]

Pull request overview

This PR aims to mitigate stack-overflow crashes (reported as potential DoS/security issues) caused by deeply recursive parsing on Linux by raising the process stack soft limit at startup via getrlimit/setrlimit.

Changes:

• Call a new utility Util::increase_stack_limit() early in main().
• Add Util::increase_stack_limit() declaration and implementation using getrlimit(RLIMIT_STACK) / setrlimit(RLIMIT_STACK).

Show a summary per file

File	Description
app/exiv2.cpp	Calls the new stack-limit adjustment helper during startup.
app/app_utils.hpp	Declares the new Util::increase_stack_limit() helper and documents intent.
app/app_utils.cpp	Implements stack limit bump using getrlimit/setrlimit when available.

Copilot's findings

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• Files reviewed: 3/3 changed files
• Comments generated: 4

[Copilot]

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 3

[kmilos]

So how come it isn't a problem on Windows if it has 8x smaller stack limit by default?

[kevinbackhouse]

So how come it isn't a problem on Windows if it has 8x smaller stack limit by default?

Oh, you're right. I got confused about the sizes. I've never actually tried to reproduce one of these issues on Windows, so I'm not sure what happens. Based on some googling, I think it might be possible to configure a larger stack size in the build system for Windows.

[kevinbackhouse]

I've updated the description. I'll need to run some tests to see if there are similar problems (and solutions) on other platforms (Windows, MacOS). I'll do that in separate PRs though.