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ftpd: escape chroot prior to re-executing ls helper

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When we merely chdir to saved "real" root fd,
exec("proc/self/exe") works for static executables but not
for dynamic ones (they can't find their interpreter).

With this patch, we also *chroot* to real root.
As a bonus, this gives us proper usernames, timezone conversion
etc.

function                                             old     new   delta
popen_ls                                             203     259     +56
ftpd_main                                           2362    2366      +4

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2014-06-27 12:24:39 +02:00
parent 5f8daefb83
commit a6ae999b3b
1 changed files with 21 additions and 32 deletions
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53
networking/ftpd.c
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@ -620,16 +620,12 @@ popen_ls(const char *opt)
const char *argv[5];
struct fd_pair outfd;
pid_t pid;
#if !BB_MMU
int cur_fd = xopen(".", O_RDONLY | O_DIRECTORY);
#endif
argv[0] = "ftpd";
argv[1] = opt; /* "-l" or "-1" */
#if BB_MMU
argv[2] = "--";
#else
/* NOMMU ftpd ls helper chdirs to argv[2],
* preventing peer from seeing real root. */
argv[2] = xrealloc_getcwd_or_warn(NULL);
#endif
argv[3] = G.ftp_arg;
argv[4] = NULL;
@ -651,16 +647,6 @@ popen_ls(const char *opt)
pid = BB_MMU ? xfork() : xvfork();
if (pid == 0) {
/* child */
#if !BB_MMU
/* On NOMMU, we want to execute a child - copy of ourself.
* In chroot we usually can't do it. Thus we chdir
* out of the chroot back to original root,
* and (see later below) execute bb_busybox_exec_path
* relative to current directory */
if (fchdir(G.root_fd) != 0)
_exit(127);
/*close(G.root_fd); - close_on_exec_on() took care of this */
#endif
/* NB: close _first_, then move fd! */
close(outfd.rd);
xmove_fd(outfd.wr, STDOUT_FILENO);
@ -674,19 +660,25 @@ popen_ls(const char *opt)
/* memset(&G, 0, sizeof(G)); - ls_main does it */
exit(ls_main(ARRAY_SIZE(argv) - 1, (char**) argv));
#else
/* + 1: we must use relative path here if in chroot.
* For example, execv("/proc/self/exe") will fail, since
* it looks for "/proc/self/exe" _relative to chroot!_ */
execv(bb_busybox_exec_path + 1, (char**) argv);
/* On NOMMU, we want to execute a child - copy of ourself
* in order to unblock parent after vfork.
* In chroot we usually can't re-exec. Thus we escape
* out of the chroot back to original root.
*/
if (G.root_fd >= 0) {
if (fchdir(G.root_fd) != 0 || chroot(".") != 0)
_exit(127);
/*close(G.root_fd); - close_on_exec_on() took care of this */
}
/* Child expects directory to list on fd #3 */
xmove_fd(cur_fd, 3);
execv(bb_busybox_exec_path, (char**) argv);
_exit(127);
#endif
}
/* parent */
close(outfd.wr);
#if !BB_MMU
free((char*)argv[2]);
#endif
return outfd.rd;
}
@ -705,8 +697,6 @@ handle_dir_common(int opts)
if (!(opts & USE_CTRL_CONN) && !port_or_pasv_was_seen())
return; /* port_or_pasv_was_seen emitted error response */
/* -n prevents user/groupname display,
* which can be problematic in chroot */
ls_fd = popen_ls((opts & LONG_LISTING) ? "-l" : "-1");
ls_fp = xfdopen_for_read(ls_fd);
/* FIXME: filenames with embedded newlines are mishandled */
@ -1139,11 +1129,10 @@ int ftpd_main(int argc UNUSED_PARAM, char **argv)
opts = getopt32(argv, "l1vS" IF_FEATURE_FTP_WRITE("w") "t:T:", &G.timeout, &abs_timeout, &G.verbose, &verbose_S);
if (opts & (OPT_l|OPT_1)) {
/* Our secret backdoor to ls */
/* TODO: pass -n? It prevents user/group resolution, which may not work in chroot anyway */
/* TODO: pass -A? It shows dot files */
/* TODO: pass --group-directories-first? would be nice, but ls doesn't do that yet */
xchdir(argv[2]);
argv[2] = (char*)"--";
if (fchdir(3) != 0)
_exit(127);
/* memset(&G, 0, sizeof(G)); - ls_main does it */
return ls_main(argc, argv);
}
@ -1185,9 +1174,9 @@ int ftpd_main(int argc UNUSED_PARAM, char **argv)
G.root_fd = xopen("/", O_RDONLY | O_DIRECTORY);
close_on_exec_on(G.root_fd);
#endif
if (argv[optind]) {
xchroot(argv[optind]);
argv += optind;
if (argv[0]) {
xchroot(argv[0]);
}
//umask(077); - admin can set umask before starting us