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Always throw the right exception in connect

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When `nix::connect` is called with a socket path that's too long, it
forks a process that will `chdir` to the directory of the socket path
and call `::connect` with the relative path (which is hopefully
short-enough).

That works fairly well, except that an exception raised in this
subprocess won't be forwarded to the parent process. Instead the logic
will just notice that the subprocess exited with a non-zero error code,
and throw a generic `Error`. In particular, any failure in the
`::connect` call should throw a `SysError` with the correct error code,
but that's not the case.

Some places try to catch this `SysError` and look at its error code (to
potentially restart for example). But this doesn't work since the
actual error that gets thrown isn't a `SysError`.

Fix that by forwarding the `errno` in case something gets wrong (by
setting the subprocess exit code to it), and throwing a `SysError` with
the right error code in the parent process.
This commit is contained in:
Théophane Hufschmitt 2022-06-15 18:07:13 +02:00
parent 6c0e7450de
commit 2d651ad2d0
1 changed files with 24 additions and 11 deletions
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35
src/libutil/util.cc
View file

@ -1817,19 +1817,32 @@ void connect(int fd, const std::string & path)
if (path.size() + 1 >= sizeof(addr.sun_path)) {
Pid pid = startProcess([&]() {
Path dir = dirOf(path);
if (chdir(dir.c_str()) == -1)
throw SysError("chdir to '%s' failed", dir);
std::string base(baseNameOf(path));
if (base.size() + 1 >= sizeof(addr.sun_path))
throw Error("socket path '%s' is too long", base);
memcpy(addr.sun_path, base.c_str(), base.size() + 1);
if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
throw SysError("cannot connect to socket at '%s'", path);
_exit(0);
try {
Path dir = dirOf(path);
if (chdir(dir.c_str()) == -1)
throw SysError("chdir to '%s' failed", dir);
std::string base(baseNameOf(path));
if (base.size() + 1 >= sizeof(addr.sun_path))
throw Error("socket path '%s' is too long", base);
memcpy(addr.sun_path, base.c_str(), base.size() + 1);
if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
throw SysError("cannot connect to socket at '%s'", path);
_exit(0);
} catch (SysError & e) {
// If this raised a `SysError`, we want to rethrow it in the
// parent process.
// For that, we need to transmit the associated error code,
// which we do by setting it as the return code for the process.
_exit(e.errNo);
} catch (std::exception &) {
_exit(-1);
}
});
int status = pid.wait();
if (status != 0)
if (status > 0) {
errno = status;
throw SysError("cannot connect to socket at '%s'", path);
} else if (status < 0)
throw Error("cannot connect to socket at '%s'", path);
} else {
memcpy(addr.sun_path, path.c_str(), path.size() + 1);