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Read secret files through unbuffered streams - #1365
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ReadFileIntoBuffer and the wolfsshd host-key and /etc/shadow readers turn off stdio buffering right after open, so those secrets are read straight into wolfSSH's own buffers instead of being staged in a libc FILE buffer that fclose frees without wiping. Public-key lists stay buffered. - port.h: add WFSETNOBUF, setvbuf(_IONBF) for stdio ports, a no-op elsewhere - wolfsshd: add wolfSSHD_OpenSecretFile, the unbuffered secure open - test_configuration: the secret open reads no further than asked, the secure open reads ahead Issue: F-14689, F-14690
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🟢 Approval recommended
No active review issues remain for the secret-file buffering changes.
No open issues 🎉
What changed in this PR
This PR disables stdio buffering when wolfSSH reads secret files, reducing the risk of leaving secret data in libc buffers freed without wiping.
Changes:
- Adds
WFSETNOBUF, with a no-op fallback for non-stdio ports. - Uses unbuffered streams for library file loading, daemon host private keys, and
/etc/shadow. - Adds tests verifying that secret streams avoid read-ahead while public-file streams retain buffering.
| File | Description |
|---|---|
wolfssh/port.h |
Adds the portable WFSETNOBUF macro. |
src/ssh.c |
Disables buffering before reading files into memory. |
apps/wolfsshd/wolfsshd.c |
Routes host private keys through the secret-file opener. |
apps/wolfsshd/test/test_configuration.c |
Tests secret and public stream read-ahead behavior. |
apps/wolfsshd/auth.h |
Declares the secret-file opening helper. |
apps/wolfsshd/auth.c |
Implements the helper and uses it for shadow-file reads. |
Review effort: Balanced
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Fenrir Automated Review — PR #1365
Scan targets checked: wolfssh-src, wolfssh-bugs
Not reviewed (no scan target covers them): apps/wolfsshd/auth.h
Coverage: 4 of 5 in-scope changed file(s) opened by the reviewer; not opened: apps/wolfsshd/test/test_configuration.c
Fenrir result: Approved ✅
No new issues found in the changed files.
Advisory only — this automated result does not count as a GitHub approval.
Review tier: Lite
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Private keys and /etc/shadow are read with stdio buffering off, so the
secrets are not left in a libc FILE buffer that fclose frees unwiped.
test_configuration coverage
Issue: F-14689, F-14690