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Clean up and relnote shebangless script support

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This adds a test for shebangless support from #7802, cleans up some of
its tricks, and includes it in the changelog.
This commit is contained in:
ridiculousfish
2021-03-27 16:07:57 -07:00
parent 0048730a67
commit eb71e4555f
4 changed files with 93 additions and 12 deletions
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24
src/exec.cpp
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@@ -63,6 +63,9 @@ enum class launch_result_t {
failed,
} __warn_unused_type;
/// This is a 'looks like text' check.
/// \return true if either there is no NUL byte, or there is a line containing a lowercase letter
/// before the first NUL byte.
static bool is_thompson_shell_payload(const char *p, size_t n) {
if (!memchr(p, '\0', n)) return true;
bool haslower = false;
@@ -87,15 +90,16 @@ static bool is_thompson_shell_payload(const char *p, size_t n) {
/// is usually uppercase, e.g. PNG, JFIF, MZ, etc. These rules are also
/// flexible enough to permit scripts with concatenated binary content,
/// such as Actually Portable Executable.
/// N.B.: this is called after fork, it must not allocate heap memory.
bool is_thompson_shell_script(const char *path) {
int e = errno;
bool res = false;
int fd = open(path, O_RDONLY | O_NOCTTY);
int fd = open_cloexec(path, O_RDONLY | O_NOCTTY);
if (fd != -1) {
char buf[256];
ssize_t got = read(fd, buf, sizeof(buf));
close(fd);
if (got != -1 && is_thompson_shell_payload(buf, got)) {
if (got >= 0 && is_thompson_shell_payload(buf, static_cast<size_t>(got))) {
res = true;
}
}
@@ -119,12 +123,22 @@ bool is_thompson_shell_script(const char *path) {
err = errno;
// The shebang wasn't introduced until UNIX Seventh Edition, so if
// the kernel won't run the binary we hand it off to the intpreter
// the kernel won't run the binary we hand it off to the interpreter
// after performing a binary safety check, recommended by POSIX: a
// line needs to exist before the first \0 with a lowercase letter
if (err == ENOEXEC && is_thompson_shell_script(actual_cmd)) {
*--argv = const_cast<char *>(_PATH_BSHELL);
execve(_PATH_BSHELL, argv, envv);
// Construct new argv.
// We must not allocate memory, so only 128 args are supported.
constexpr size_t maxargs = 128;
size_t nargs = 0;
while (argv[nargs]) nargs++;
if (nargs <= maxargs) {
char *argv2[1 + maxargs + 1]; // +1 for /bin/sh, +1 for terminating nullptr
char interp[] = _PATH_BSHELL;
argv2[0] = interp;
std::copy_n(argv, 1 + nargs, &argv2[1]); // +1 to copy terminating nullptr
execve(_PATH_BSHELL, argv2, envv);
}
}
errno = err;