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>

diff --git a/include/c.h b/include/c.h
index 3f47dbdcb3ebfb1f5f830ddc69293b2f53bd3995..a5162b96403d3bdf347aa1dcc8724e682d9dcdc5 100644 (file)
--- a/include/c.h
+++ b/include/c.h
@@ -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
  */

diff --git a/lib/idcache.c b/lib/idcache.c
index a1a957b9313069c7664ef2bd614249c1ae24ce50..2facf13e025188d029c0eb0a5f79c0a033e0150f 100644 (file)
--- a/lib/idcache.c
+++ b/lib/idcache.c
@@ -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;

diff --git a/term-utils/agetty.c b/term-utils/agetty.c
index 449dfef3c463fa129f9b5de7f011ae578ed31061..0b22104deb8ec58a09b5783a2887ce239cbffaa7 100644 (file)
--- a/term-utils/agetty.c
+++ b/term-utils/agetty.c
@@ -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 */