(release/25.2) xf86: prevent passing NULL pointer as strcat() destination

[metux]

Backport of #3568 (master)

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]

Review: xf86: prevent passing NULL pointer as strcat() destination

Replaces realloc + assert with XNFrealloc (which calls FatalError on failure) in xf86parseFilesSection for both file_fontpath and file_modulepath. This eliminates the -Wanalyzer-null-argument warnings from GCC 16.1 (passing potentially-NULL realloc result to strcat) and the associated -Wanalyzer-malloc-leak warnings (old pointer not freed on failure path).

Code review (1 file, +3/-4)

• XNFrealloc (os/alloc.c:44): wraps realloc, calls FatalError("XNFrealloc: Out of memory") on failure — same termination behavior as the old assert, but without the UB of passing NULL to strcat. The assert was also unsafe in release builds where NDEBUG strips it.
• #include "os.h" added for the XNFrealloc declaration. Correct header — same pattern used elsewhere in the xf86 parser.
• No behavioral change: both paths (assert failure / FatalError) abort the server. The difference is that XNFrealloc is safe in all build configurations.

Checklist

• Driver ABI: No impact — internal xf86 parser, no exported symbols changed.
• Security: Not a security fix — compiler warning cleanup for static analysis false-positive paths.
• Backport: Warning fix only, not a runtime/crash fix. Already on release/25.2. Maintainer decides for release/25.1/release/25.0.
• CI: Queued, not yet completed.

Verdict

Passed. Clean, minimal fix. Follows established XNFrealloc pattern used throughout the codebase.