From mboxrd@z Thu Jan  1 00:00:00 1970
From: Claude Code Review Bot <claude-review@example.com>
To: dri-devel-reviews@example.com
Subject: Claude review: scripts: modpost: detect and report truncated buf_printf() output
Date: Tue, 05 May 2026 10:17:58 +1000
Message-ID: <review-patch1-20260430-nova-exports-v1-1-7ca31664e983@nvidia.com>
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References: <20260430-nova-exports-v1-0-7ca31664e983@nvidia.com> <20260430-nova-exports-v1-1-7ca31664e983@nvidia.com>
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Patch Review

**Verdict: Good bugfix, should likely be submitted independently.**

This is a genuine pre-existing bug. When `vsnprintf` returns `len >=3D SZ`,=
 the current code passes that unclamped length to `buf_write`, which reads =
`len` bytes from a buffer that only has `SZ` bytes =E2=80=94 a classic buff=
er over-read:

```c
len =3D vsnprintf(tmp, SZ, fmt, ap);
buf_write(buf, tmp, len);
```

The fix correctly checks both error return (`len < 0`) and truncation (`len=
 >=3D SZ`):

```c
if (len < 0) {
    perror("vsnprintf failed");
    exit(1);
}
if (len >=3D SZ)
    fatal("buf_printf output was truncated: %d bytes needed, %d available\n=
",
          len + 1, SZ);
```

Minor nits:

1. The error message says `%d available` but prints `SZ` (the buffer size).=
 Since `vsnprintf` reserves one byte for the NUL terminator, `SZ` is the bu=
ffer capacity, not the available character count. `len + 1` is the needed b=
ytes *including* NUL, and `SZ` is available *including* NUL, so this is con=
sistent =E2=80=94 but it could be clearer. Consider wording like "needed %d=
 bytes but buffer is only %d" without the `+1`.

2. This patch is a standalone bugfix applicable to all of modpost, not Nova=
-specific. It would benefit from being submitted separately or at minimum n=
oted as such in the cover letter, since it could be picked up independently.

---
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