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lpd: much safer against malicious input. Does not fork anymore,

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as this is not needed.
This commit is contained in:
Denis Vlasenko 2008-03-24 01:52:52 +00:00
parent 0b6c6a9c9f
commit 39c77c3738
1 changed files with 125 additions and 92 deletions
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217
printutils/lpd.c
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@ -64,7 +64,7 @@ static char *sane(char *str)
char *s = str;
char *p = s;
while (*s) {
if (isalnum(*s) || '-' == *s) {
if (isalnum(*s) || '-' == *s || '_' == *s) {
*p++ = *s;
}
s++;
@ -73,100 +73,85 @@ static char *sane(char *str)
return str;
}
/* vfork() disables some optimizations. Moving its use
* to minimal, non-inlined function saves bytes */
static NOINLINE void vfork_close_stdio_and_exec(char **argv)
// we can use leaky setenv since we are about to exec or exit
static void exec_helper(char **filenames, char **argv) ATTRIBUTE_NORETURN;
static void exec_helper(char **filenames, char **argv)
{
if (vfork() == 0) {
// CHILD
// we are the helper. we wanna be silent.
// this call reopens stdio fds to "/dev/null"
// (no daemonization is done)
bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO | DAEMON_ONLY_SANITIZE, NULL);
BB_EXECVP(*argv, argv);
_exit(127);
}
}
char *p, *q;
char var[2];
static void exec_helper(const char *fname, char **argv)
{
char *p, *q, *file;
char *our_env[12];
int env_idx;
// read control file
file = q = xmalloc_open_read_close(fname, NULL);
// delete control file
unlink(fname);
// read and delete ctrlfile
q = xmalloc_open_read_close(filenames[0], NULL);
unlink(filenames[0]);
// provide datafile name
xsetenv("DATAFILE", filenames[1]);
// parse control file by "\n"
env_idx = 0;
while ((p = strchr(q, '\n')) != NULL
&& isalpha(*q)
&& env_idx < ARRAY_SIZE(our_env)
) {
*p++ = '\0';
// here q is a line of <SYM><VALUE>
// let us set environment string <SYM>=<VALUE>
// N.B. setenv is leaky!
// We have to use putenv(malloced_str),
// and unsetenv+free (in parent)
our_env[env_idx] = xasprintf("%c=%s", *q, q+1);
putenv(our_env[env_idx]);
env_idx++;
var[0] = *q++;
var[1] = '\0';
xsetenv(var, q);
// next line, plz!
q = p;
}
free(file);
vfork_close_stdio_and_exec(argv);
// PARENT (or vfork error)
// clean up...
while (--env_idx >= 0) {
*strchrnul(our_env[env_idx], '=') = '\0';
unsetenv(our_env[env_idx]);
}
// we are the helper, we wanna be silent.
// this call reopens stdio fds to "/dev/null"
// (no daemonization is done)
bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO | DAEMON_ONLY_SANITIZE, NULL);
BB_EXECVP(*argv, argv);
exit(0);
}
static char *xmalloc_read_stdin(void)
{
size_t max = 4 * 1024; /* more than enough for commands! */
// SECURITY:
size_t max = 4 * 1024; // more than enough for commands!
return xmalloc_reads(STDIN_FILENO, NULL, &max);
}
int lpd_main(int argc, char *argv[]) MAIN_EXTERNALLY_VISIBLE;
int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
{
int spooling;
int spooling = spooling; // for compiler
int seen;
char *s, *queue;
// read command
s = xmalloc_read_stdin();
// we understand only "receive job" command
if (2 != *s) {
unsupported_cmd:
printf("Command %02x %s\n",
(unsigned char)s[0], "is not supported");
return EXIT_FAILURE;
}
char *filenames[2];
// goto spool directory
if (*++argv)
xchdir(*argv++);
// parse command: "\x2QUEUE_NAME\n"
queue = s + 1;
*strchrnul(s, '\n') = '\0';
// error messages of xfuncs will be sent over network
xdup2(STDOUT_FILENO, STDERR_FILENO);
filenames[0] = NULL; // ctrlfile name
filenames[1] = NULL; // datafile name
// read command
s = queue = xmalloc_read_stdin();
// we understand only "receive job" command
if (2 != *queue) {
unsupported_cmd:
printf("Command %02x %s\n",
(unsigned char)s[0], "is not supported");
goto err_exit;
}
// parse command: "2 | QUEUE_NAME | '\n'"
queue++;
// protect against "/../" attacks
// *strchrnul(queue, '\n') = '\0'; - redundant, sane() will do
if (!*sane(queue))
return EXIT_FAILURE;
// queue is a directory -> chdir to it and enter spooling mode
spooling = chdir(queue) + 1; /* 0: cannot chdir, 1: done */
xdup2(STDOUT_FILENO, STDERR_FILENO);
spooling = chdir(queue) + 1; // 0: cannot chdir, 1: done
seen = 0;
// we don't free(queue), we might need it later
while (1) {
char *fname;
@ -176,30 +161,65 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
int expected_len, real_len;
// signal OK
write(STDOUT_FILENO, "", 1);
safe_write(STDOUT_FILENO, "", 1);
// get subcommand
// valid s must be of form: "SUBCMD | LEN | space | FNAME"
// N.B. we bail out on any error
s = xmalloc_read_stdin();
if (!s)
return EXIT_SUCCESS; // probably EOF
if (!s) { // (probably) EOF
if (spooling /* && 6 != spooling - always true */) {
// we didn't see both ctrlfile & datafile!
goto err_exit;
}
// one of only two non-error exits
return EXIT_SUCCESS;
}
// validate input.
// we understand only "control file" or "data file" cmds
if (2 != s[0] && 3 != s[0])
goto unsupported_cmd;
if (seen & (s[0] - 1)) {
printf("Duplicated subcommand\n");
goto err_exit;
}
seen &= (s[0] - 1); // bit 1: ctrlfile; bit 2: datafile
// get filename
*strchrnul(s, '\n') = '\0';
// valid s must be of form: SUBCMD | LEN | SP | FNAME
// N.B. we bail out on any error
fname = strchr(s, ' ');
if (!fname) {
printf("Command %02x %s\n",
(unsigned char)s[0], "lacks filename");
return EXIT_FAILURE;
// bad_fname:
printf("No or bad filename\n");
goto err_exit;
}
*fname++ = '\0';
// // s[0]==2: ctrlfile, must start with 'c'
// // s[0]==3: datafile, must start with 'd'
// if (fname[0] != s[0] + ('c'-2))
// goto bad_fname;
// get length
expected_len = bb_strtou(s + 1, NULL, 10);
if (errno || expected_len < 0) {
printf("Bad length\n");
goto err_exit;
}
if (2 == s[0] && expected_len > 16 * 1024) {
// SECURITY:
// ctrlfile can't be big (we want to read it back later!)
printf("File is too big\n");
goto err_exit;
}
// open the file
if (spooling) {
// spooling mode: dump both files
// job in flight has mode 0200 "only writable"
fd = xopen3(sane(fname), O_CREAT | O_WRONLY | O_TRUNC | O_EXCL, 0200);
sane(fname);
fd = open3_or_warn(fname, O_CREAT | O_WRONLY | O_TRUNC | O_EXCL, 0200);
if (fd < 0)
goto err_exit;
filenames[s[0] - 2] = xstrdup(fname);
} else {
// non-spooling mode:
// 2: control file (ignoring), 3: data file
@ -207,35 +227,48 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
if (3 == s[0])
fd = xopen(queue, O_RDWR | O_APPEND);
}
expected_len = xatoi_u(s + 1);
// copy the file
real_len = bb_copyfd_size(STDIN_FILENO, fd, expected_len);
if (spooling && real_len != expected_len) {
unlink(fname); // don't keep corrupted files
if (real_len != expected_len) {
printf("Expected %d but got %d bytes\n",
expected_len, real_len);
return EXIT_FAILURE;
}
// chmod completely downloaded file as "readable+writable" ...
if (spooling) {
fchmod(fd, 0600);
// ... and accumulate dump state.
// N.B. after all files are dumped spooling should be 1+2+3==6
spooling += s[0];
}
close(fd); // NB: can do close(-1). Who cares?
// are all files dumped? -> spawn spool helper
if (6 == spooling && *argv) {
fname[0] = 'c'; // pass control file name
exec_helper(fname, argv);
goto err_exit;
}
// get ACK and see whether it is NUL (ok)
if (read(STDIN_FILENO, s, 1) != 1 || s[0] != 0) {
if (safe_read(STDIN_FILENO, s, 1) != 1 || s[0] != 0) {
// don't send error msg to peer - it obviously
// don't follow the protocol, so probably
// it can't understand us either
return EXIT_FAILURE;
goto err_exit;
}
if (spooling) {
// chmod completely downloaded file as "readable+writable"
fchmod(fd, 0600);
// accumulate dump state
// N.B. after all files are dumped spooling should be 1+2+3==6
spooling += s[0];
}
free(s);
} /* while (1) */
close(fd); // NB: can do close(-1). Who cares?
// spawn spool helper and exit if all files are dumped
if (6 == spooling && *argv) {
// signal OK
safe_write(STDOUT_FILENO, "", 1);
// does not return (exits 0)
exec_helper(filenames, argv);
}
} // while (1)
err_exit:
// don't keep corrupted files
if (spooling) {
if (filenames[0])
unlink(filenames[0]);
if (filenames[1])
unlink(filenames[1]);
}
return EXIT_FAILURE;
}