diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/xspawn.c | 321 |
1 files changed, 240 insertions, 81 deletions
diff --git a/src/xspawn.c b/src/xspawn.c index e739c5f..dc2bf67 100644 --- a/src/xspawn.c +++ b/src/xspawn.c @@ -274,11 +274,219 @@ fail: return -1; } +/** + * Context for resolving executables in the $PATH. + */ +struct bfs_resolver { + /** The executable to spawn. */ + const char *exe; + /** The $PATH to resolve in. */ + char *path; + /** A buffer to hold the resolved path. */ + char *buf; + /** The size of the buffer. */ + size_t len; + /** Whether the executable is already resolved. */ + bool done; + /** Whether to free(path). */ + bool free; +}; + +/** Free a $PATH resolution context. */ +static void bfs_resolve_free(struct bfs_resolver *res) { + if (res->free) { + free(res->path); + } + free(res->buf); +} + +/** Get the next component in the $PATH. */ +static bool bfs_resolve_next(const char **path, const char **next, size_t *len) { + *path = *next; + if (!*path) { + return false; + } + + *next = strchr(*path, ':'); + if (*next) { + *len = *next - *path; + ++*next; + } else { + *len = strlen(*path); + } + + if (*len == 0) { + // POSIX 8.3: "A zero-length prefix is a legacy feature that + // indicates the current working directory." + *path = "."; + *len = 1; + } + + return true; +} + +/** Finish resolving an executable, potentially from the child process. */ +static int bfs_resolve_late(struct bfs_resolver *res) { + if (res->done) { + return 0; + } + + char *buf = res->buf; + char *end = buf + res->len; + + const char *path; + const char *next = res->path; + size_t len; + while (bfs_resolve_next(&path, &next, &len)) { + char *cur = xstpencpy(buf, end, path, len); + cur = xstpecpy(cur, end, "/"); + cur = xstpecpy(cur, end, res->exe); + if (cur == end) { + bfs_bug("PATH resolution buffer too small"); + errno = ENOMEM; + return -1; + } + + if (xfaccessat(AT_FDCWD, buf, X_OK) == 0) { + res->exe = buf; + res->done = true; + return 0; + } + + if (end) { + path = end + 1; + } else { + errno = ENOENT; + return -1; + } + } + + return 0; +} + +/** Check if we can skip path resolution entirely. */ +static bool bfs_can_skip_resolve(const struct bfs_resolver *res, const struct bfs_spawn *ctx) { + if (ctx && !(ctx->flags & BFS_SPAWN_USE_PATH)) { + return true; + } + + if (strchr(res->exe, '/')) { + return true; + } + + return false; +} + +/** Check if any $PATH components are relative. */ +static bool bfs_resolve_relative(const struct bfs_resolver *res) { + const char *path; + const char *next = res->path; + size_t len; + while (bfs_resolve_next(&path, &next, &len)) { + if (path[0] != '/') { + return true; + } + } + + return false; +} + +/** Check if we can resolve the executable before file actions. */ +static bool bfs_can_resolve_early(const struct bfs_resolver *res, const struct bfs_spawn *ctx) { + if (!bfs_resolve_relative(res)) { + return true; + } + + if (ctx) { + for_slist (const struct bfs_spawn_action, action, ctx) { + if (action->op == BFS_SPAWN_FCHDIR) { + return false; + } + } + } + + return true; +} + +/** Get the required path resolution buffer size. */ +static size_t bfs_resolve_capacity(const struct bfs_resolver *res) { + size_t max = 0; + + const char *path; + const char *next = res->path; + size_t len; + while (bfs_resolve_next(&path, &next, &len)) { + if (len > max) { + max = len; + } + } + + // path + "/" + exe + '\0' + return max + 1 + strlen(res->exe) + 1; +} + +/** Begin resolving an executable, from the parent process. */ +static int bfs_resolve_early(struct bfs_resolver *res, const char *exe, const struct bfs_spawn *ctx) { + *res = (struct bfs_resolver) { + .exe = exe, + }; + + if (bfs_can_skip_resolve(res, ctx)) { + res->done = true; + return 0; + } + + res->path = getenv("PATH"); + if (!res->path) { +#if defined(_CS_PATH) + res->path = xconfstr(_CS_PATH); + res->free = true; +#elif defined(_PATH_DEFPATH) + res->path = _PATH_DEFPATH; +#else + errno = ENOENT; +#endif + } + if (!res->path) { + goto fail; + } + + bool can_finish = bfs_can_resolve_early(res, ctx); + bool use_posix = ctx && (ctx->flags & BFS_SPAWN_USE_POSIX); + if (!can_finish && use_posix) { + // posix_spawnp() will do the resolution, so don't bother + // allocating a buffer + return 0; + } + + res->len = bfs_resolve_capacity(res); + res->buf = malloc(res->len); + if (!res->buf) { + goto fail; + } + + if (can_finish && bfs_resolve_late(res) != 0) { + goto fail; + } + + return 0; + +fail: + bfs_resolve_free(res); + return -1; +} + #if _POSIX_SPAWN > 0 /** bfs_spawn() implementation using posix_spawn(). */ -static pid_t bfs_posix_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp) { +static pid_t bfs_posix_spawn(struct bfs_resolver *res, const struct bfs_spawn *ctx, char **argv, char **envp) { pid_t ret; - errno = posix_spawn(&ret, exe, &ctx->actions, &ctx->attr, argv, envp); + + if (res->done) { + errno = posix_spawn(&ret, res->exe, &ctx->actions, &ctx->attr, argv, envp); + } else { + errno = posix_spawnp(&ret, res->exe, &ctx->actions, &ctx->attr, argv, envp); + } + if (errno != 0) { return -1; } @@ -288,7 +496,7 @@ static pid_t bfs_posix_spawn(const char *exe, const struct bfs_spawn *ctx, char #endif /** Actually exec() the new process. */ -static noreturn void bfs_spawn_exec(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp, int pipefd[2]) { +static noreturn void bfs_spawn_exec(struct bfs_resolver *res, const struct bfs_spawn *ctx, char **argv, char **envp, int pipefd[2]) { xclose(pipefd[0]); for_slist (const struct bfs_spawn_action, action, ctx) { @@ -345,11 +553,14 @@ static noreturn void bfs_spawn_exec(const char *exe, const struct bfs_spawn *ctx } } - execve(exe, argv, envp); + if (bfs_resolve_late(res) != 0) { + goto fail; + } - int error; -fail: - error = errno; + execve(res->exe, argv, envp); + +fail:; + int error = errno; // In case of a write error, the parent will still see that we exited // unsuccessfully, but won't know why @@ -360,7 +571,7 @@ fail: } /** bfs_spawn() implementation using fork()/exec(). */ -static pid_t bfs_fork_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp) { +static pid_t bfs_fork_spawn(struct bfs_resolver *res, const struct bfs_spawn *ctx, char **argv, char **envp) { // Use a pipe to report errors from the child int pipefd[2]; if (pipe_cloexec(pipefd) != 0) { @@ -374,7 +585,7 @@ static pid_t bfs_fork_spawn(const char *exe, const struct bfs_spawn *ctx, char * return -1; } else if (pid == 0) { // Child - bfs_spawn_exec(exe, ctx, argv, envp, pipefd); + bfs_spawn_exec(res, ctx, argv, envp, pipefd); } // Parent @@ -394,26 +605,23 @@ static pid_t bfs_fork_spawn(const char *exe, const struct bfs_spawn *ctx, char * } /** Call the right bfs_spawn() implementation. */ -static pid_t bfs_spawn_impl(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp) { +static pid_t bfs_spawn_impl(struct bfs_resolver *res, const struct bfs_spawn *ctx, char **argv, char **envp) { #if _POSIX_SPAWN > 0 if (ctx->flags & BFS_SPAWN_USE_POSIX) { - return bfs_posix_spawn(exe, ctx, argv, envp); + return bfs_posix_spawn(res, ctx, argv, envp); } #endif - return bfs_fork_spawn(exe, ctx, argv, envp); + return bfs_fork_spawn(res, ctx, argv, envp); } pid_t bfs_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp) { // execvp()/posix_spawnp() are typically implemented with repeated // execv() calls for each $PATH component until one succeeds. It's // faster to resolve the full path ahead of time. - char *resolved = NULL; - if (ctx->flags & BFS_SPAWN_USE_PATH) { - exe = resolved = bfs_spawn_resolve(exe); - if (!resolved) { - return -1; - } + struct bfs_resolver res; + if (bfs_resolve_early(&res, exe, ctx) != 0) { + return -1; } extern char **environ; @@ -421,78 +629,29 @@ pid_t bfs_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char envp = environ; } - pid_t ret = bfs_spawn_impl(exe, ctx, argv, envp); - free(resolved); + pid_t ret = bfs_spawn_impl(&res, ctx, argv, envp); + bfs_resolve_free(&res); return ret; } char *bfs_spawn_resolve(const char *exe) { - if (strchr(exe, '/')) { - return strdup(exe); - } - - const char *path = getenv("PATH"); - - char *confpath = NULL; - if (!path) { -#if defined(_CS_PATH) - path = confpath = xconfstr(_CS_PATH); -#elif defined(_PATH_DEFPATH) - path = _PATH_DEFPATH; -#else - errno = ENOENT; -#endif + struct bfs_resolver res; + if (bfs_resolve_early(&res, exe, NULL) != 0) { + return NULL; } - if (!path) { + if (bfs_resolve_late(&res) != 0) { + bfs_resolve_free(&res); return NULL; } - size_t cap = 0; - char *ret = NULL; - while (true) { - const char *end = strchr(path, ':'); - size_t len = end ? (size_t)(end - path) : strlen(path); - - // POSIX 8.3: "A zero-length prefix is a legacy feature that - // indicates the current working directory." - if (len == 0) { - path = "."; - len = 1; - } - - size_t total = len + 1 + strlen(exe) + 1; - if (cap < total) { - char *grown = realloc(ret, total); - if (!grown) { - goto fail; - } - ret = grown; - cap = total; - } - - memcpy(ret, path, len); - if (ret[len - 1] != '/') { - ret[len++] = '/'; - } - strcpy(ret + len, exe); - - if (xfaccessat(AT_FDCWD, ret, X_OK) == 0) { - break; - } - - if (!end) { - errno = ENOENT; - goto fail; - } - - path = end + 1; + char *ret; + if (res.exe == res.buf) { + ret = res.buf; + res.buf = NULL; + } else { + ret = strdup(res.exe); } - free(confpath); + bfs_resolve_free(&res); return ret; - -fail: - free(confpath); - free(ret); - return NULL; } |