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popen(): Add 'e' mode character to set close-on-exec on the new fd.

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If 'e' is used, the kernel must support the recently added pipe2() system
call.

The use of pipe2() with O_CLOEXEC also fixes race conditions between
concurrent popen() calls from different threads, even if the close-on-exec
flag on the fd of the returned FILE is later cleared (because popen() closes
all file descriptors from earlier popen() calls in the child process).
Therefore, this approach should be used in all cases when pipe2() can be
assumed present.

The old version of popen() rejects "re" and "we" but treats "r+e" like "r+".
This commit is contained in:
Jilles Tjoelker 2013-05-20 17:31:18 +00:00
parent 95beb4525d
commit e9dec7758d
3 changed files with 31 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
lib/libc/gen/popen.3
View File

@ -28,7 +28,7 @@
.\" @(#)popen.3 8.2 (Berkeley) 5/3/95
.\" $FreeBSD$
.\"
.Dd May 3, 1995
.Dd May 20, 2013
.Dt POPEN 3
.Os
.Sh NAME
@ -79,6 +79,11 @@ for writing, or
.Ql r+
for reading and writing.
.Pp
A letter
.Ql e
may be appended to that to request that the underlying file descriptor
be set close-on-exec.
.Pp
The
.Fa command
argument is a pointer to a null-terminated string

30
lib/libc/gen/popen.c
View File

@ -43,6 +43,7 @@ __FBSDID("$FreeBSD$");
#include <signal.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
@ -71,10 +72,11 @@ popen(command, type)
{
struct pid *cur;
FILE *iop;
int pdes[2], pid, twoway;
int pdes[2], pid, twoway, cloexec;
char *argv[4];
struct pid *p;
cloexec = strchr(type, 'e') != NULL;
/*
* Lite2 introduced two-way popen() pipes using _socketpair().
* FreeBSD's pipe() is bidirectional, so we use that.
@ -84,10 +86,11 @@ popen(command, type)
type = "r+";
} else {
twoway = 0;
if ((*type != 'r' && *type != 'w') || type[1])
if ((*type != 'r' && *type != 'w') ||
(type[1] && (type[1] != 'e' || type[2])))
return (NULL);
}
if (pipe(pdes) < 0)
if ((cloexec ? pipe2(pdes, O_CLOEXEC) : pipe(pdes)) < 0)
return (NULL);
if ((cur = malloc(sizeof(struct pid))) == NULL) {
@ -120,20 +123,29 @@ popen(command, type)
* the compiler is free to corrupt all the local
* variables.
*/
(void)_close(pdes[0]);
if (!cloexec)
(void)_close(pdes[0]);
if (pdes[1] != STDOUT_FILENO) {
(void)_dup2(pdes[1], STDOUT_FILENO);
(void)_close(pdes[1]);
if (!cloexec)
(void)_close(pdes[1]);
if (twoway)
(void)_dup2(STDOUT_FILENO, STDIN_FILENO);
} else if (twoway && (pdes[1] != STDIN_FILENO))
} else if (twoway && (pdes[1] != STDIN_FILENO)) {
(void)_dup2(pdes[1], STDIN_FILENO);
if (cloexec)
(void)_fcntl(pdes[1], F_SETFD, 0);
} else if (cloexec)
(void)_fcntl(pdes[1], F_SETFD, 0);
} else {
if (pdes[0] != STDIN_FILENO) {
(void)_dup2(pdes[0], STDIN_FILENO);
(void)_close(pdes[0]);
}
(void)_close(pdes[1]);
if (!cloexec)
(void)_close(pdes[0]);
} else if (cloexec)
(void)_fcntl(pdes[0], F_SETFD, 0);
if (!cloexec)
(void)_close(pdes[1]);
}
SLIST_FOREACH(p, &pidlist, next)
(void)_close(fileno(p->fp));

8
tools/regression/lib/libc/gen/test-popen.c
View File

@ -70,10 +70,10 @@ main(int argc, char *argv[])
FILE *fp, *fp2;
int i, j, status;
const char *mode;
const char *allmodes[] = { "r", "w", "r+" };
const char *rmodes[] = { "r", "r+" };
const char *wmodes[] = { "w", "r+" };
const char *rwmodes[] = { "r+" };
const char *allmodes[] = { "r", "w", "r+", "re", "we", "r+e", "re+" };
const char *rmodes[] = { "r", "r+", "re", "r+e", "re+" };
const char *wmodes[] = { "w", "r+", "we", "r+e", "re+" };
const char *rwmodes[] = { "r+", "r+e", "re+" };
char buf[80];
struct sigaction act, oact;