casaroli opened a new pull request, #21135:
URL: https://github.com/apache/nuttx/pull/21135
## Summary
**fs/v9fs: Fail readlink() of a file that is not a symbolic link.**
`readlink()` of a regular file or a directory must fail with `EINVAL`. v9fs
sent `Treadlink` for any file. With the "mapped" security models of QEMU
(`security_model=mapped-xattr` or `mapped-file`), a symbolic link is stored on
the host as a regular file that holds the target, and the server answers
`Treadlink` for any regular file with its contents:
- `readlink("/etc/hostname")` returned the host name, with no error;
- `readlink()` of a large file gives a reply that does not fit the receive
buffer: QEMU stops the 9p device (`Failed to encode VirtFS reply type 23`) and
the caller waits forever. CPython calls `readlink()` on its own executable at
start, so every Python run hung on such a root file system.
The change gets the attributes of the file (`Tgetattr`) first and returns
`-EINVAL` when it is not a symbolic link. A directory now also gives `EINVAL`
(it gave `EISDIR`).
## Impact
- `readlink()` on a v9fs volume behaves as POSIX requires with every server
security model. With `security_model=none` or `passthrough` nothing changes for
regular files (the host `readlink()` already failed with `EINVAL`).
- One more round trip (`Tgetattr`) per `readlink()` call.
- Same behavior in flat, protected and kernel builds; v9fs code only, no
architecture code.
## Testing
Test program `readlinkreg.c` on the 9p volume `/system` of
`qemu-armv8a:knsh` (kernel build) with `CONFIG_FS_LINKS=y`, QEMU with HVF,
`-fsdev local,...,security_model=mapped-xattr`:
| Case | master | this PR |
|---|---|---|
| `readlink()` of a small regular file: -1 `EINVAL` | FAIL (returns 8, the
contents) | PASS |
| `readlink()` of a directory: -1 `EINVAL` | FAIL (`EISDIR`) | PASS |
| `readlink()` of a symbolic link: the target | PASS | PASS |
| `readlink()` of a 64 KiB regular file: -1 `EINVAL` | FAIL (returns 0) |
PASS |
ostest exits with status 0 on `qemu-armv8a:knsh` and `qemu-armv8a:nsh`.
Build check with `CONFIG_FS_V9FS=y`: qemu-armv8a:nsh, qemu-armv8a:knsh,
rv-virt:nsh64, rv-virt:pnsh64, rv-virt:knsh64, qemu-intel64:knsh_romfs,
sim:nsh, qemu-armv7a:knsh: all OK, `v9fs.c` compiled in each.
`tools/checkpatch.sh -c -u -m -g` passes.
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