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improve robustness of wordexp and fix handling of 0-word case 

avoid using exit status to determine if a shell error occurred, since
broken programs may install SIGCHLD handlers which reap all zombies,
including ones that don't belong to them. using clone and __WCLONE
does not seem to work for avoiding this problem since exec resets the
exit signal to SIGCHLD.

instead, the new code uses a dummy word at the beginning of the
shell's output, which is ignored, to determine whether the command was
executed successfully. this also fixes a corner case where a word
string containing zero words was interpreted as a single zero-length
word rather than no words at all. POSIX does not seem to require this
case to be supported anyway, though.

in addition, the new code uses the correct retry idiom for waitpid to
ensure that spurious STOP/CONT signals in the child and/or EINTR in
the parent do not prevent successful wait for the child, and blocks
signals in the child.
This commit is contained in:
Rich Felker 2013-11-22 15:29:14 -05:00
parent a516077feb
commit d8f1908b82
1 changed files with 16 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
src/misc/wordexp.c
View File

@ -7,7 +7,8 @@
#include <stdlib.h>
#include <sys/wait.h>
#include <signal.h>
#include <pthread.h>
#include <errno.h>
#include "pthread_impl.h"
static char *getword(FILE *f)
{
@ -28,6 +29,7 @@ static int do_wordexp(const char *s, wordexp_t *we, int flags)
char **wv = 0;
int p[2];
pid_t pid;
sigset_t set;
if (flags & WRDE_REUSE) wordfree(we);
@ -87,7 +89,9 @@ static int do_wordexp(const char *s, wordexp_t *we, int flags)
}
if (pipe(p) < 0) return WRDE_NOSPACE;
__block_all_sigs(&set);
pid = fork();
__restore_sigs(&set);
if (pid < 0) {
close(p[0]);
close(p[1]);
@ -98,7 +102,7 @@ static int do_wordexp(const char *s, wordexp_t *we, int flags)
close(p[0]);
close(p[1]);
execl("/bin/sh", "sh", "-c",
"eval \"printf %s\\\\\\\\0 $1 $2\"",
"eval \"printf %s\\\\\\\\0 x $1 $2\"",
"sh", s, redir, (char *)0);
_exit(1);
}
@ -114,6 +118,14 @@ static int do_wordexp(const char *s, wordexp_t *we, int flags)
l = wv ? i+1 : 0;
free(getword(f));
if (feof(f)) {
fclose(f);
while ((waitpid(pid, &status, 0) < 0 && errno == EINTR)
|| !WIFEXITED(status));
return WRDE_SYNTAX;
}
while ((w = getword(f))) {
if (i+1 >= l) {
l += l/2+10;
@ -127,15 +139,8 @@ static int do_wordexp(const char *s, wordexp_t *we, int flags)
if (!feof(f)) err = WRDE_NOSPACE;
fclose(f);
waitpid(pid, &status, 0);
if (WEXITSTATUS(status)) {
if (!(flags & WRDE_APPEND)) {
free(wv);
return WRDE_SYNTAX;
} else if (wv==we->we_wordv) {
return WRDE_SYNTAX;
}
}
while ((waitpid(pid, &status, 0) < 0 && errno == EINTR)
|| !WIFEXITED(status));
we->we_wordv = wv;
we->we_wordc = i;