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authorLaurent Bercot <ska-skaware@skarnet.org>2022-01-16 02:12:02 +0000
committerLaurent Bercot <ska@appnovation.com>2022-01-16 02:12:02 +0000
commit2588893b126bb596733b508114a5380839a3df72 (patch)
tree4c4f7b23e78573d4485e6c7407506f463ccc9425 /src
parentf61cc5fc0f2e7f6dd042aeea20e3107b689c703d (diff)
downloads6-linux-init-2588893b126bb596733b508114a5380839a3df72.tar.xz
ctty-passing doesn't look satanic anymore, thx Leah
Signed-off-by: Laurent Bercot <ska@appnovation.com>
Diffstat (limited to 'src')
-rw-r--r--src/init/s6-linux-init.c99
1 files changed, 22 insertions, 77 deletions
diff --git a/src/init/s6-linux-init.c b/src/init/s6-linux-init.c
index 2cf3c09..c7873be 100644
--- a/src/init/s6-linux-init.c
+++ b/src/init/s6-linux-init.c
@@ -87,12 +87,24 @@ static void kbspecials (void)
strerr_warnwu1sys("trap ctrl-alt-del") ;
}
-static inline void run_stage2 (char const *basedir, char const **argv, unsigned int argc, char const *const *envp, size_t envlen, char const *modifs, size_t modiflen, char const *initdefault)
+static inline void run_stage2 (char const *basedir, char const **argv, unsigned int argc, char const *const *envp, size_t envlen, char const *modifs, size_t modiflen, char const *initdefault, char const *tty)
{
size_t dirlen = strlen(basedir) ;
char const *childargv[argc + 3] ;
char fn[dirlen + sizeof("/scripts/" STAGE2)] ;
PROG = "s6-linux-init (child)" ;
+
+ if (setsid() == -1) strerr_diefu1sys(111, "setsid") ;
+ if (tty)
+ {
+ int fd = openb_read(tty) ;
+ if (fd == -1) strerr_warnwu2sys("open ", tty) ;
+ else if (fd_move(0, fd) == -1)
+ {
+ strerr_warnwu3sys("make ", tty, " into new stdin") ;
+ close(fd) ;
+ }
+ }
memcpy(fn, basedir, dirlen) ;
memcpy(fn + dirlen, "/scripts/" STAGE2, sizeof("/scripts/" STAGE2)) ;
childargv[0] = fn ;
@@ -117,79 +129,6 @@ static inline void run_stage2 (char const *basedir, char const **argv, unsigned
xmexec_fm(childargv, envp, envlen, modifs, modiflen) ;
}
-/*
- This is ugly voodoo, keep away from innocent eyes.
- If ttyfd exists, it means we're in a "docker run -it" container or
-equivalent, and tty (name of the original stdin) is a ctty. We don't
-want the supervision tree to have this ctty (else ^C kills everything)
-but we want stage 2 to keep it if possible, so that if we have a CMD run
-by stage 2 (as is the case with s6-overlay), it remains interactive, i.e.
-control sequences can be sent to it.
- We cannot have the child (future stage 2) steal the ctty from the parent
-(future s6-svscan) via TIOCSCTTY because we may not have the permissions for
-it: Docker containers don't give CAP_SYS_ADMIN to pid 1, and user containers
-are a thing.
- So instead, we have the parent relinquish the ctty, then the child reopen
-it - which makes it a ctty for the child. This requires /dev/pts to be
-pre-mounted, but that's usually the case. Even if it's not, the child doesn't
-get its ctty, but at least the parent doesn't have it anymore.
- Pipes are used for synchronization.
-*/
-
-static inline pid_t fork_and_setup_session (char const *tty)
-{
- pid_t pid ;
- if (!tty)
- {
- pid = fork() ;
- if (pid == -1) strerr_diefu1sys(111, "fork") ;
- setsid() ;
- }
- else
- {
- int p[2][2] ;
- int r ;
- char c ;
- if (pipe(p[0]) == -1 || pipe(p[1])) strerr_diefu1sys(111, "pipe") ;
- pid = fork() ;
- if (pid == -1) strerr_diefu1sys(111, "fork") ;
- if (pid)
- {
- close(p[0][1]) ;
- close(p[1][0]) ;
- r = read(p[0][0], &c, 1) ;
- if (r == -1) strerr_diefu2sys(111, "read from ", "child") ;
- if (!r) strerr_dief2x(111, "child", " died") ;
- close(p[0][0]) ;
- if (ioctl(1, TIOCNOTTY) == -1) strerr_warnwu1sys("relinquish controlling terminal") ;
- if (write(p[1][1], "", 1) < 1) strerr_diefu2sys(111, "write to ", "child") ;
- close(p[1][1]) ;
- }
- else
- {
- int fd ;
- PROG = "s6-linux-init (child)" ;
- close(p[1][1]) ;
- close(p[0][0]) ;
- if (setsid() == -1) strerr_diefu1sys(111, "setsid") ;
- if (write(p[0][1], "", 1) < 1) strerr_diefu2sys(111, "write to ", "parent") ;
- close(p[0][1]) ;
- r = read(p[1][0], &c, 1) ;
- if (r == -1) strerr_diefu2sys(111, "read from ", "parent") ;
- if (!r) strerr_dief2x(111, "parent", " died") ;
- close(p[1][0]) ;
- fd = openb_read(tty) ;
- if (fd == -1) strerr_warnwu2sys("open ", tty) ;
- else if (fd_move(0, fd) == -1)
- {
- strerr_warnwu3sys("make ", tty, " into new stdin") ;
- close(fd) ;
- }
- }
- }
- return pid ;
-}
-
int main (int argc, char const **argv, char const *const *envp)
{
mode_t mask = 0022 ;
@@ -238,7 +177,7 @@ int main (int argc, char const **argv, char const *const *envp)
if (inns)
{
char c ;
- ssize_t r = read(3, &c, 1) ;
+ ssize_t r = read(3, &c, 1) ; /* Docker synchronization protocol */
if (r < 0)
{
if (errno != EBADF) strerr_diefu1sys(111, "read from fd 3") ;
@@ -333,6 +272,7 @@ int main (int argc, char const **argv, char const *const *envp)
}
{
+ pid_t pid ;
char const *newenvp[2] = { 0, 0 } ;
size_t pathlen = path ? strlen(path) : 0 ;
char fmtfd[2 + UINT_FMT] = "-" ;
@@ -347,8 +287,13 @@ int main (int argc, char const **argv, char const *const *envp)
newenvp[0] = pathvar ;
}
if (nologger && pipe(notifpipe) < 0) strerr_diefu1sys(111, "pipe") ;
- if (!fork_and_setup_session(tty))
- run_stage2(basedir, argv, argc, newenvp, !!path, envmodifs.s, envmodifs.len, initdefault) ;
+ if (tty && ioctl(1, TIOCNOTTY) == -1) strerr_warnwu1sys("relinquish control terminal") ;
+
+ pid = fork() ;
+ if (pid == -1) strerr_diefu1sys(111, "fork") ;
+ if (!pid) run_stage2(basedir, argv, argc, newenvp, !!path, envmodifs.s, envmodifs.len, initdefault, tty) ;
+
+ setsid() ; /* just in case our caller is something weird */
if (nologger)
{
close(notifpipe[0]) ;