From 65a8b859a9a3f2bb4a62c15ca1f4d01288593734 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Wed, 26 Oct 2016 22:29:11 +0200 Subject: [PATCH] ash: optimize tryexec(): avoid one allocation There was a bug in tryexec which bbox had fixed in 2003. dash had a smaller fix in 2007. Copy it. It is smaller, although it is also more quirky (requires argv[-1] to exist). Upstream commit 1: Date: Mon, 15 Oct 2007 20:24:28 +0800 [EXEC] Fixed execing of scripts with no hash-bang The function tryexec used the original name instead of the path found through PATH search. This patch fixes that. Test case: trap 'rm -f $TMP' EXIT TMP=$(tempfile -s nosuchthing) cat <<- EOF > $TMP echo OK EOF chmod u+x $TMP cd / PATH=${TMP%/*} ${TMP##*/} Old result: /bin/sh: Can't open filelgY4Fanosuchthing New result: OK Upstream commit 2: Date: Sun, 23 Dec 2007 11:02:26 +0800 [EVAL] Fix bad pointer arithmetic in evalcommand dash dies on sparc with a SIGBUS due to an arithmetic error introduced with commit 03b4958, this patch fixes it. Signed-off-by: Herbert Xu function old new delta evalcommand 1261 1264 +3 dotcmd 321 319 -2 tryexec 115 64 -51 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 1/2 up/down: 3/-53) Total: -50 bytes Signed-off-by: Denys Vlasenko --- shell/ash.c | 31 +++++++++++-------------------- 1 file changed, 11 insertions(+), 20 deletions(-) diff --git a/shell/ash.c b/shell/ash.c index 8bf02e6a7..133b2d40e 100644 --- a/shell/ash.c +++ b/shell/ash.c @@ -7467,13 +7467,7 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) char *cmd, char **argv, char ** #else execve(cmd, argv, envp); #endif - if (cmd == (char*) bb_busybox_exec_path) { - /* We already visited ENOEXEC branch below, don't do it again */ -//TODO: try execve(initial_argv0_of_shell, argv, envp) before giving up? - free(argv); - return; - } - if (errno == ENOEXEC) { + if (cmd != (char*) bb_busybox_exec_path && errno == ENOEXEC) { /* Run "cmd" as a shell script: * http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html * "If the execve() function fails with ENOEXEC, the shell @@ -7490,19 +7484,13 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) char *cmd, char **argv, char ** * message and exit code 126. For one, this prevents attempts * to interpret foreign ELF binaries as shell scripts. */ - char **ap; - char **new; - - for (ap = argv; *ap; ap++) - continue; - new = ckmalloc((ap - argv + 2) * sizeof(new[0])); - new[0] = (char*) "ash"; - new[1] = cmd; - ap = new + 2; - while ((*ap++ = *++argv) != NULL) - continue; + argv[0] = cmd; cmd = (char*) bb_busybox_exec_path; - argv = new; + /* NB: this is only possible because all callers of shellexec() + * ensure that the argv[-1] slot exists! + */ + argv--; + argv[0] = (char*) "ash"; goto repeat; } } @@ -7510,6 +7498,7 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) char *cmd, char **argv, char ** /* * Exec a program. Never returns. If you change this routine, you may * have to change the find_command routine as well. + * argv[-1] must exist and be writable! See tryexec() for why. */ static void shellexec(char **, const char *, int) NORETURN; static void @@ -9415,7 +9404,9 @@ evalcommand(union node *cmd, int flags) argc++; } - argv = nargv = stalloc(sizeof(char *) * (argc + 1)); + /* Reserve one extra spot at the front for shellexec. */ + nargv = stalloc(sizeof(char *) * (argc + 2)); + argv = ++nargv; for (sp = arglist.list; sp; sp = sp->next) { TRACE(("evalcommand arg: %s\n", sp->text)); *nargv++ = sp->text; -- 2.25.1