(release/25.1) xf86: prevent passing NULL pointer as strcat() destination

[metux]

Reported by gcc 16.1:
hw/xfree86/parser/Files.c:119:17: warning: use of NULL where non-null
expected [CWE-476] [-Wanalyzer-null-argument]
119 | strcat(ptr->file_fontpath, ",");
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
......
117 | ptr->file_fontpath = realloc(ptr->file_fontpath, i);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (9) when ‘realloc’ fails
| (10) using NULL here
118 | if (j)
| ~
| |
| (11) following ‘true’ branch (when ‘j != 0’)... ─>─┐
| │
| │
|┌──────────────────────────────────────────────────────────────────┘
119 |│ strcat(ptr->file_fontpath, ",");
|│ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|│ |
|└───────────────>(12) ...to here
| (13) ⚠ argument 1 (‘realloc(*ptr.file_fontpath, (long unsigned int)i)’) NULL where non-null expected
: note: argument 1 of ‘__builtin_strlen’ must be non-null
......
| │
|┌──────────────────────────────────────────────────────────────────┘
121 |│ strcat(ptr->file_fontpath, str);
|│ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|│ | |
|│ | (10) using NULL here
|└───────────>(9) ...to here
| (11) ⚠ argument 1 (‘*ptr.file_fontpath’) NULL where non-null expected
note: argument 1 of ‘strcat’ must be non-null

hw/xfree86/parser/Files.c:144:17: warning: use of NULL where non-null expected [CWE-476] [-Wanalyzer-null-argument]
144 | strcat(ptr->file_modulepath, ",");
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
......
142 | ptr->file_modulepath = realloc(ptr->file_modulepath, k);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (9) when ‘realloc’ fails
| (10) using NULL here
143 | if (l)
| ~
| |
| (11) following ‘true’ branch (when ‘l != 0’)... ─>─┐
| │
| │
|┌──────────────────────────────────────────────────────────────────┘
144 |│ strcat(ptr->file_modulepath, ",");
|│ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|│ |
|└───────────────>(12) ...to here
| (13) ⚠ argument 1 (‘realloc(*ptr.file_modulepath, (long unsigned int)k)’) NULL where non-null expected
: note: argument 1 of ‘__builtin_strlen’ must be non-null
......
| │
|┌──────────────────────────────────────────────────────────────────┘
146 |│ strcat(ptr->file_modulepath, str);
|│ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|│ | |
|│ | (10) using NULL here
|└───────────>(9) ...to here
| (11) ⚠ argument 1 (‘*ptr.file_modulepath’) NULL where non-null expected
note: argument 1 of ‘strcat’ must be non-null

Also clears two -Wanalyzer-malloc-leak warnings for leaking the old
pointer when realloc() failed, now that realloc() cannot fail.

Signed-off-by: Alan Coopersmith alan.coopersmith@oracle.com
Part-of: https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2272

[metux]

🤖 Automated review — generated by Starfleet ship Discovery on behalf of @metux. Not a human review.

Clean companion fix to #3567 — no objections.

What it does: replaces bare realloc() + assert() with XNFrealloc() in two font/module path allocation sites in xf86parseFilesSection(). Same pattern as PR #3567 (strcpy case in xf86Configure.c): XNFrealloc aborts on OOM, eliminating the NULL-dereference on strcat() and the malloc-leak on realloc failure. Also adds #include "os.h" for the XNFrealloc declaration.

Fixes gcc 16.1 warnings:

• Two -Wanalyzer-null-argument (realloc NULL passed to strcat)
• Two -Wanalyzer-malloc-leak (old pointer leaked when realloc failed)

ABI impact: none. Parser-internal, no struct or export changes.

Backport candidate: yes — NULL-dereference fix (CWE-476), same rationale as #3567. Likely applies to release/25.0 as well.

Verdict: passes review.