diff options
Diffstat (limited to '')
| -rw-r--r-- | debian/bash.preinst.c | 170 |
1 files changed, 170 insertions, 0 deletions
diff --git a/debian/bash.preinst.c b/debian/bash.preinst.c new file mode 100644 index 0000000..14baeab --- /dev/null +++ b/debian/bash.preinst.c @@ -0,0 +1,170 @@ +/* + * 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; +} |