From 8c16f38a8886fdf5e12762a9c0c427e2fd1eb688 Mon Sep 17 00:00:00 2001 From: Johnothan King Date: Thu, 23 Jul 2020 17:20:26 -0700 Subject: [PATCH] Fix an infinite loop related to $_ if ksh is /bin/sh (#90) The following explanation is mostly taken from Tomas Klacko's report on the old mailing list (which also contains a C program reproducer) [*]: 1. When ksh starts a binary, it sets its environment variable "_" to "*number*/path/to/binary". Where "number" is the pid of the ksh process. 2. The binary forks and the child executes a suid root shell script which begins with #!/bin/sh. For this bug to occur, ksh must be /bin/sh. 3. The ksh process interpreting the suid shell script leaves the "_" variable as not set (nv_getval(L_ARGNOD) returns NULL) because the "number" from step 1 is not the pid of its parent process. 4-5. Because "_" is not set and the script is suid root, an infinite loop occurs because when the SHELL environment variable contains "/bin/sh" pathshell() returns "/bin/sh". This becomes an infinite loop of /bin/sh /dev/fd/3 executing /bin/sh /dev/fd/3. src/cmd/ksh93/sh/init.c: get_lastarg(): - Disable the check for if the "number" refers to the process id of the parent process. src/cmd/ksh93/sh/main.c: sh_main(): - Prevent an infinite loop when '$_' is not passed in from the environment. Solaris applies this bugfix to their version of ksh: https://github.com/oracle/solaris-userland/blob/master/components/ksh93/patches/190-17432413.patch [*]: https://www.mail-archive.com/ast-developers@lists.research.att.com/msg01680.html --- NEWS | 2 ++ src/cmd/ksh93/sh/init.c | 2 +- src/cmd/ksh93/sh/main.c | 2 +- 3 files changed, 4 insertions(+), 2 deletions(-) diff --git a/NEWS b/NEWS index a18d893321b8..e4d97c321825 100644 --- a/NEWS +++ b/NEWS @@ -5,6 +5,8 @@ Any uppercase BUG_* names are modernish shell bug IDs. 2020-07-23: +- Fixed an infinite loop that could occur when ksh is the system's /bin/sh. + - A command substitution that is run on the same line as a here-document will no longer cause a syntax error. diff --git a/src/cmd/ksh93/sh/init.c b/src/cmd/ksh93/sh/init.c index 5b91a232b6fb..2ca5a3c72fb0 100644 --- a/src/cmd/ksh93/sh/init.c +++ b/src/cmd/ksh93/sh/init.c @@ -710,7 +710,7 @@ static char* get_lastarg(Namval_t* np, Namfun_t *fp) char *cp; int pid; if(sh_isstate(SH_INIT) && (cp=shp->lastarg) && *cp=='*' && (pid=strtol(cp+1,&cp,10)) && *cp=='*') - nv_putval(np,(pid==shp->gd->ppid?cp+1:0),0); + nv_putval(np,cp+1,0); return(shp->lastarg); } diff --git a/src/cmd/ksh93/sh/main.c b/src/cmd/ksh93/sh/main.c index ebcfee9ff134..2670a280eebe 100644 --- a/src/cmd/ksh93/sh/main.c +++ b/src/cmd/ksh93/sh/main.c @@ -273,7 +273,7 @@ int sh_main(int ac, char *av[], Shinit_f userinit) * try to undo effect of solaris 2.5+ * change for argv for setuid scripts */ - if(((type = sh_type(cp = av[0])) & SH_TYPE_SH) && (!(name = nv_getval(L_ARGNOD)) || !((type = sh_type(cp = name)) & SH_TYPE_SH))) + if(((type = sh_type(cp = av[0])) & SH_TYPE_SH) && (name = nv_getval(L_ARGNOD)) && (!((type = sh_type(cp = name)) & SH_TYPE_SH))) { av[0] = (type & SH_TYPE_LOGIN) ? cp : path_basename(cp); /* exec to change $0 for ps */