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/*
* This file is in the public domain.
* You may freely use, modify, distribute, and relicense it.
*/
#include "bash.preinst.h"
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
static void backup(const char *file, const char *dest)
{
const char * const cmd[] = {"cp", "-dp", file, dest, NULL};
if (exists(file))
run(cmd);
}
static void force_symlink(const char *target, const char *link,
const char *temp)
{
/*
* Forcibly create a symlink to "target" from "link".
* This is performed in two stages with an
* intermediate temporary file because symlink(2) cannot
* atomically replace an existing file.
*/
if ((unlink(temp) && errno != ENOENT) ||
symlink(target, temp) ||
rename(temp, link))
die_errno("cannot create symlink %s -> %s", link, target);
}
static void reset_diversion(const char *package, const char *file,
const char *distrib)
{
const char * const remove_old_diversion[] =
{"dpkg-divert", "--package", "bash", "--remove", file, NULL};
const char * const new_diversion[] =
{"dpkg-divert", "--package", package,
"--divert", distrib, "--add", file, NULL};
run(remove_old_diversion);
run(new_diversion);
}
static int has_binsh_line(FILE *file)
{
char item[sizeof("/bin/sh\n")];
while (fgets(item, sizeof(item), file)) {
int ch;
if (!memcmp(item, "/bin/sh\n", strlen("/bin/sh\n") + 1))
return 1;
if (strchr(item, '\n'))
continue;
/* Finish the line. */
for (ch = 0; ch != '\n' && ch != EOF; ch = fgetc(file))
; /* just reading */
if (ch == EOF)
break;
}
if (ferror(file))
die_errno("cannot read pipe");
return 0;
}
static int binsh_in_filelist(const char *package)
{
const char * const cmd[] = {"dpkg-query", "-L", package, NULL};
pid_t child;
int sink;
FILE *in;
int found;
/*
* dpkg -L $package 2>/dev/null | ...
*
* Redirection of stderr is for quieter output
* when $package is not installed. If opening /dev/null
* fails, no problem; leave stderr alone in that case.
*/
sink = open("/dev/null", O_WRONLY);
if (sink >= 0)
set_cloexec(sink);
in = spawn_pipe(&child, cmd, sink);
/* ... | grep "^/bin/sh\$" */
found = has_binsh_line(in);
if (fclose(in))
die_errno("cannot close read end of pipe");
/*
* dpkg -L will error out if $package is not already installed.
*
* We stopped reading early if we found a match, so
* tolerate SIGPIPE in that case.
*/
wait_or_die(child, "dpkg-query -L", ERROR_OK |
(found ? SIGPIPE_OK : 0));
return found;
}
static int undiverted(const char *path)
{
const char * const cmd[] =
{"dpkg-divert", "--listpackage", path, NULL};
pid_t child;
char packagename[sizeof("bash\n")];
size_t len;
FILE *in = spawn_pipe(&child, cmd, -1);
int diverted = 1;
/* Is $path diverted by someone other than bash? */
len = fread(packagename, 1, sizeof(packagename), in);
if (ferror(in))
die_errno("cannot read from dpkg-divert");
if (len == 0)
diverted = 0; /* No diversion. */
if (len == strlen("bash\n") && !memcmp(packagename, "bash\n", len))
diverted = 0; /* Diverted by bash. */
if (fclose(in))
die_errno("cannot close read end of pipe");
wait_or_die(child, "dpkg-divert", ERROR_OK | SIGPIPE_OK);
return !diverted;
}
int main(int argc, char *argv[])
{
/* /bin/sh needs to point to a valid target. */
if (access("/bin/sh", X_OK)) {
backup("/bin/sh", "/bin/sh.distrib");
backup("/usr/share/man/man1/sh.1.gz",
"/usr/share/man/man1/sh.distrib.1.gz");
force_symlink("bash", "/bin/sh", "/bin/sh.temp");
force_symlink("bash.1.gz", "/usr/share/man/man1/sh.1.gz",
"/usr/share/man/man1/sh.1.gz.temp");
}
if (!binsh_in_filelist("bash"))
/* Ready. */
return 0;
/*
* In bash (<= 4.1-3), the bash package included symlinks for
* /bin/sh and the sh(1) manpage in its data.tar.
*
* Unless we are careful, unpacking the new version of bash
* will remove them. So we tell dpkg that the files from bash
* to be removed are elsewhere, using a diversion on behalf of
* another package.
*
* Based on an idea by Michael Stone.
* “You're one sick individual.” -- Anthony Towns
* http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=85;bug=34717
*/
if (undiverted("/bin/sh"))
reset_diversion("dash", "/bin/sh", "/bin/sh.distrib");
if (undiverted("/usr/share/man/man1/sh.1.gz"))
reset_diversion("dash", "/usr/share/man/man1/sh.1.gz",
"/usr/share/man/man1/sh.distrib.1.gz");
return 0;
}
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