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agetty: fix characters reorder in login prompt 

The current agetty uses TIOCSTI ioctl to return already read chars
from login name back to the terminal (without read() before
tcsetattr() we will lost data already written by user). The ioctl
based solution is fragile due to race -- we can return chars when
terminal already contains another new chars. The result is reordered
chars in login name.

The solution is to use extra buffer for already read data.

Reported-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Karel Zak 2017-03-27 14:54:39 +02:00
parent ca5389757e
commit 790119b885
3 changed files with 38 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/c.h
View File

@ -25,6 +25,10 @@
# include <sys/sysmacros.h> /* for major, minor */
#endif
#ifndef LOGIN_NAME_MAX
# define LOGIN_NAME_MAX 256
#endif
/*
* Compiler-specific stuff
*/

4
lib/idcache.c
View File

@ -7,10 +7,6 @@
#include "c.h"
#include "idcache.h"
#ifndef LOGIN_NAME_MAX
#define LOGIN_NAME_MAX 256
#endif
struct identry *get_id(struct idcache *ic, unsigned long int id)
{
struct identry *ent;

46
term-utils/agetty.c
View File

@ -1581,12 +1581,12 @@ static int process_netlink(void)
return changed;
}
static int wait_for_term_input(int fd)
static int wait_for_term_input(int fd, char *prebuf, size_t prebufsz, size_t *readsz)
{
char buffer[sizeof(struct inotify_event) + NAME_MAX + 1];
struct termios orig, nonc;
fd_set rfds;
int count, i;
int count;
/* Our aim here is to fall through if something fails
* and not be stuck waiting. On failure assume we have input */
@ -1645,11 +1645,11 @@ static int wait_for_term_input(int fd)
tcsetattr(fd, TCSANOW, &orig);
/* Reinject the bytes we read back into the buffer, usually just one byte */
for (i = 0; i < count; i++)
ioctl(fd, TIOCSTI, buffer + i);
if (count > 0 && prebuf && prebufsz) {
memcpy(prebuf, buffer, min(sizeof(buffer), prebufsz));
*readsz = count;
}
/* Have terminal input */
return 1;
} else if (netlink_fd >= 0 && FD_ISSET(netlink_fd, &rfds)) {
@ -1718,14 +1718,15 @@ again:
if (op->flags & F_LOGINPAUSE) {
puts(_("[press ENTER to login]"));
#ifdef AGETTY_RELOAD
if (!wait_for_term_input(STDIN_FILENO)) {
if (!wait_for_term_input(STDIN_FILENO, NULL, 0, NULL)) {
/* reload issue */
if (op->flags & F_VCONSOLE)
termio_clear(STDOUT_FILENO);
goto again;
}
#endif
#else
getc(stdin);
#endif
}
#ifdef KDGKBLED
if (!(op->flags & F_NOHINTS) && !op->autolog &&
@ -1844,13 +1845,26 @@ static char *get_logname(struct options *op, struct termios *tp, struct chardata
*bp = '\0';
while (*logname == '\0') {
char prebuf[LOGIN_NAME_MAX] = { 0 };
size_t presz = 0, precur = 0;
/* Write issue file and prompt */
do_prompt(op, tp);
#ifdef AGETTY_RELOAD
/* If asked to reprompt *before* terminal input arrives, then do so */
if (!wait_for_term_input(STDIN_FILENO)) {
/* If asked to reprompt *before* terminal input arrives, then do so.
*
* Note that wait_for_term_input() calls read() and the result
* is stored to the 'prebuf'. We need this to avoid data lost
* by terminal attributes reset (and return chars back to the
* terminal by TIOCSTI is fragile (chars reorder)).
*
* The data from 'prebuf' are not printed to the terminal yet
* (disabled ECHO in wait_for_term_input()).
*/
if (!wait_for_term_input(STDIN_FILENO,
prebuf, sizeof(prebuf), &readsz)) {
if (op->flags & F_VCONSOLE)
termio_clear(STDOUT_FILENO);
continue;
@ -1862,8 +1876,15 @@ static char *get_logname(struct options *op, struct termios *tp, struct chardata
while (cp->eol == '\0') {
char key;
int force_echo = 0;
if (read(STDIN_FILENO, &c, 1) < 1) {
/* use already read data from buffer */
if (presz && precur < presz) {
c = prebuf[precur++];
force_echo = 1;
/* read from terminal */
} else if (read(STDIN_FILENO, &c, 1) < 1) {
/* The terminal could be open with O_NONBLOCK when
* -L (force CLOCAL) is specified... */
@ -1939,13 +1960,14 @@ static char *get_logname(struct options *op, struct termios *tp, struct chardata
break;
if ((size_t)(bp - logname) >= sizeof(logname) - 1)
log_err(_("%s: input overrun"), op->tty);
if ((tp->c_lflag & ECHO) == 0)
if ((tp->c_lflag & ECHO) == 0 || force_echo)
write_all(1, &c, 1); /* echo the character */
*bp++ = ascval; /* and store it */
break;
}
}
}
#ifdef HAVE_WIDECHAR
if ((op->flags & (F_EIGHTBITS|F_UTF8)) == (F_EIGHTBITS|F_UTF8)) {
/* Check out UTF-8 multibyte characters */