BufferOverflow Hardening

[Abdullah-Ebryx]

Added a new argument to chroot_realpath to support small buffers.
As discussed in the previous pull request, this change helps avoid technical debt and enforces a security boundary by design, rather than relying on the programmer to implement it correctly.

Summary by Sourcery

Harden chroot_realpath against buffer overflows by adding an explicit buffer size parameter to its signature, updating all callers and the test harness to supply buffer length, and using the size in snprintf.

Enhancements:

• Add size_resolved_path parameter to chroot_realpath signature in criu.c, utils.c, and chroot_realpath.c
• Use size_resolved_path in snprintf calls within chroot_realpath to cap output length
• Update all chroot_realpath invocations to pass the buffer size argument

Tests:

• Update test_chroot_realpath in the fuzzer to supply buffer size to the new chroot_realpath signature

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Introduces a size parameter to chroot_realpath and updates its implementation and all callers to use explicit buffer lengths for safer path resolution.

Class diagram for updated chroot_realpath function signature and usage

classDiagram
    class chroot_realpath {
        +char *chroot_realpath(const char *chroot, const char *path, char resolved_path[], size_t size_resolved_path)
    }
    class libcrun_container_checkpoint_linux_criu {
        +calls chroot_realpath(..., buf, sizeof(buf))
    }
    class libcrun_container_restore_linux_criu {
        +calls chroot_realpath(..., buf, sizeof(buf))
    }
    class safe_openat_fallback {
        +calls chroot_realpath(..., buffer, sizeof(buffer))
    }
    libcrun_container_checkpoint_linux_criu --> chroot_realpath
    libcrun_container_restore_linux_criu --> chroot_realpath
    safe_openat_fallback --> chroot_realpath

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File-Level Changes

Change	Details	Files
Extended chroot_realpath signature to accept buffer size	Added size_resolved_path parameter to function prototypes in criu.c and utils.c Updated chroot_realpath definition to include size_resolved_path Adjusted test declarations to match new signature	src/libcrun/criu.c src/libcrun/utils.c src/libcrun/chroot_realpath.c tests/tests_libcrun_fuzzer.c
Updated all chroot_realpath calls to pass buffer lengths	Replaced calls that passed only buf with buf and sizeof(buf) Ensured correct sizeof() usage in criu.c, utils.c, and tests	src/libcrun/criu.c src/libcrun/utils.c tests/tests_libcrun_fuzzer.c
Switched snprintf usage to use size_resolved_path	Replaced hardcoded PATH_MAX with size_resolved_path in snprintf calls Maintained overflow check logic against size_resolved_path	src/libcrun/chroot_realpath.c

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[sourcery-ai]

Hey there - I've reviewed your changes and they look great!

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location> `src/libcrun/chroot_realpath.c:138` </location>
<code_context>
 			/* If a component doesn't exist, then return what we could translate. */
 			if (errno == ENOENT) {
-				int ret = snprintf (resolved_path, PATH_MAX, "%s%s%s", got_path, path[0] == '/' || path[0] == '\0' ? "" : "/", path);
+				int ret = snprintf (resolved_path, size_resolved_path, "%s%s%s", got_path, path[0] == '/' || path[0] == '\0' ? "" : "/", path);
 				if (ret >= PATH_MAX) {
 					__set_errno(ENAMETOOLONG);
</code_context>

<issue_to_address>
**issue (bug_risk):** snprintf return value should be compared to size_resolved_path, not PATH_MAX.

Update the condition to 'if (ret >= size_resolved_path)' to ensure truncation is checked against the actual buffer size, avoiding incorrect results when size_resolved_path is less than PATH_MAX.
</issue_to_address>

### Comment 2
<location> `tests/tests_libcrun_fuzzer.c:126` </location>
<code_context>
   if (path == NULL)
     return 0;

-  chroot_realpath (".", path, resolved_path);
+  chroot_realpath (".", path, resolved_path,sizeof(resolved_path));
   (void) resolved_path;
   return 0;
</code_context>

<issue_to_address>
**suggestion (testing):** No explicit test for small buffer sizes or buffer overflow conditions.

Please add tests that pass small buffer sizes to chroot_realpath to verify it handles these cases safely and returns appropriate errors.
</issue_to_address>

### Comment 3
<location> `tests/tests_libcrun_fuzzer.c:114` </location>
<code_context>
 #  endif

 /* Defined in chroot_realpath.c  */
-char *chroot_realpath (const char *chroot, const char *path, char resolved_path[]);
+char *chroot_realpath (const char *chroot, const char *path, char resolved_path[],size_t size_resolved_path);

 static const char *console_socket = NULL;
</code_context>

<issue_to_address>
**suggestion (testing):** Fuzzer test does not assert or check the result of chroot_realpath.

Add assertions or checks for chroot_realpath's return value and errno, particularly with edge-case buffer sizes, to improve test coverage and catch regressions.
</issue_to_address>

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[giuseppe]

please squash and remove all the unrelated changes