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authorTavian Barnes <tavianator@tavianator.com>2021-06-13 15:53:06 -0400
committerTavian Barnes <tavianator@tavianator.com>2021-06-13 16:10:13 -0400
commitdb67752672877ea0f5360699cb34ad31065ef39e (patch)
tree974bed22b2ed747a2c7b9cf5b1f57a370a646df3
parentae15c5abe0bb2d8bd5fd3502721288bcb1a85d59 (diff)
downloadbfs-db67752672877ea0f5360699cb34ad31065ef39e.tar.xz
spawn: New function for resolving executables in the PATH
This fixes the BFS_SPAWN_USEPATH to use the parent's environment, not the new child's environment, to resolve the executable.
-rw-r--r--spawn.c95
-rw-r--r--spawn.h13
2 files changed, 91 insertions, 17 deletions
diff --git a/spawn.c b/spawn.c
index 82beca5..f83663a 100644
--- a/spawn.c
+++ b/spawn.c
@@ -17,7 +17,9 @@
#include "spawn.h"
#include "util.h"
#include <errno.h>
+#include <fcntl.h>
#include <stdlib.h>
+#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
@@ -139,21 +141,9 @@ int bfs_spawn_addsetrlimit(struct bfs_spawn *ctx, int resource, const struct rli
}
}
-/** Facade for execvpe() which is non-standard. */
-static int bfs_execvpe(const char *exe, char **argv, char **envp) {
-#if __GLIBC__ || __linux__ || __NetBSD__ || __OpenBSD__
- return execvpe(exe, argv, envp);
-#else
- extern char **environ;
- environ = envp;
- return execvp(exe, argv);
-#endif
-}
-
/** Actually exec() the new process. */
static void bfs_spawn_exec(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp, int pipefd[2]) {
int error;
- enum bfs_spawn_flags flags = ctx ? ctx->flags : 0;
const struct bfs_spawn_action *actions = ctx ? ctx->actions : NULL;
close(pipefd[0]);
@@ -199,11 +189,7 @@ static void bfs_spawn_exec(const char *exe, const struct bfs_spawn *ctx, char **
}
}
- if (flags & BFS_SPAWN_USEPATH) {
- bfs_execvpe(exe, argv, envp);
- } else {
- execve(exe, argv, envp);
- }
+ execve(exe, argv, envp);
fail:
error = errno;
@@ -222,6 +208,15 @@ pid_t bfs_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char
envp = environ;
}
+ enum bfs_spawn_flags flags = ctx ? ctx->flags : 0;
+ char *resolved = NULL;
+ if (flags & BFS_SPAWN_USEPATH) {
+ exe = resolved = bfs_spawn_resolve(exe);
+ if (!resolved) {
+ return -1;
+ }
+ }
+
// Use a pipe to report errors from the child
int pipefd[2];
if (pipe_cloexec(pipefd) != 0) {
@@ -244,6 +239,7 @@ pid_t bfs_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char
// Parent
close(pipefd[1]);
+ free(resolved);
ssize_t nbytes = xread(pipefd[0], &error, sizeof(error));
close(pipefd[0]);
@@ -256,3 +252,68 @@ pid_t bfs_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char
return pid;
}
+
+char *bfs_spawn_resolve(const char *exe) {
+ if (strchr(exe, '/')) {
+ return strdup(exe);
+ }
+
+ const char *path = getenv("PATH");
+
+ char *confpath = NULL;
+ if (!path) {
+ path = confpath = xconfstr(_CS_PATH);
+ if (!path) {
+ 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;
+ }
+
+ free(confpath);
+ return ret;
+
+fail:
+ free(confpath);
+ free(ret);
+ return NULL;
+}
diff --git a/spawn.h b/spawn.h
index 16815bb..7bae89c 100644
--- a/spawn.h
+++ b/spawn.h
@@ -107,4 +107,17 @@ int bfs_spawn_addsetrlimit(struct bfs_spawn *ctx, int resource, const struct rli
*/
pid_t bfs_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp);
+/**
+ * Look up an executable in the current PATH, as BFS_SPAWN_USEPATH or execvp()
+ * would do.
+ *
+ * @param exe
+ * The name of the binary to execute. Bare names without a '/' will be
+ * searched on the provided PATH.
+ * @return
+ * The full path to the executable, which should be free()'d, or NULL on
+ * failure.
+ */
+char *bfs_spawn_resolve(const char *exe);
+
#endif // BFS_SPAWN_H