From 7c945bdd6ba44bbb490504f44904ac65d705dd17 Mon Sep 17 00:00:00 2001 From: Martijn Dekker Date: Sun, 27 Oct 2024 01:34:38 +0000 Subject: [PATCH] Fix crash on 'exec' after 'unset SHLVL' (re: fa0f9796) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Vincent Mihalkovič (@vmihalko) reports: > If the user unsets the SHLVL variable and later replaces the > shell by executing a command, ksh will segfault. > > Reproducer > > # unset -v SHLVL > # exec bash > Segmaentation fault (core dumped) > > Reason > > The reason for this is that the SHLVL variable is getting > decremented without any guard making sure it's still in the > environment, see: > > src/cmd/ksh93/bltins/misc.c: > 145: /* if the main shell is about to be replaced, decrease SHLVL > to cancel out a subsequent increase */ > 146: if(!sh.realsubshell) > 147: (*SHLVL->nvalue.ip)--; This should be fixed so that SHLVL can be unset safely and lose its special properties like other special variables do. src/cmd/ksh93/sh/init.c, src/cmd/ksh93/include/shell.h: - Move the static 'shlvl' in init.c to the sh state struct, so that 'sh.shlvl' can be accessed from the entire ksh93 code base. - Change its type from int to int32_t -- this is more correct as nv_getval() uses this type to retrieve the value. In practice, this makes no difference because sizeof(int) == sizeof(int32_t), but this is not guaranteed by the standards. src/cmd/ksh93/bltins/misc.c: - Access sh.shlvl directly instead of dereferencing the SHLVL value pointer, as this pointer is invalidated upon 'unset SHLVL'. This fixes the bug. Resolves: https://github.com/ksh93/ksh/issues/788 --- src/cmd/ksh93/bltins/misc.c | 2 +- src/cmd/ksh93/include/shell.h | 1 + src/cmd/ksh93/sh/init.c | 7 +++---- src/cmd/ksh93/tests/variables.sh | 7 +++++++ 4 files changed, 12 insertions(+), 5 deletions(-) diff --git a/src/cmd/ksh93/bltins/misc.c b/src/cmd/ksh93/bltins/misc.c index cb7e883..1d49162 100644 --- a/src/cmd/ksh93/bltins/misc.c +++ b/src/cmd/ksh93/bltins/misc.c @@ -144,7 +144,7 @@ int b_exec(int argc,char *argv[], Shbltin_t *context) return 1; /* if the main shell is about to be replaced, decrease SHLVL to cancel out a subsequent increase */ if(!sh.realsubshell) - (*SHLVL->nvalue.ip)--; + sh.shlvl--; sh_onstate(SH_EXEC); if(sh.subshell && !sh.subshare) { diff --git a/src/cmd/ksh93/include/shell.h b/src/cmd/ksh93/include/shell.h index c28b159..96d982a 100644 --- a/src/cmd/ksh93/include/shell.h +++ b/src/cmd/ksh93/include/shell.h @@ -270,6 +270,7 @@ struct Shell_s * Programs using libshell should not rely on them as they may change. */ int subshell; /* set for virtual subshell */ int realsubshell; /* ${.sh.subshell}, actual subshell level (including virtual and forked) */ + int32_t shlvl; /* $SHLVL, non-subshell child shell level */ char shcomp; /* set when running shcomp */ unsigned char trapnote; /* set when trap/signal is pending */ struct sh_scoped st; /* scoped information */ diff --git a/src/cmd/ksh93/sh/init.c b/src/cmd/ksh93/sh/init.c index 1242789..1f1b71e 100644 --- a/src/cmd/ksh93/sh/init.c +++ b/src/cmd/ksh93/sh/init.c @@ -220,7 +220,6 @@ static Init_t *nv_init(void); #if SHOPT_STATS static void stat_init(void); #endif -static int shlvl; static int rand_shift; /* @@ -1352,7 +1351,7 @@ Shell_t *sh_init(int argc,char *argv[], Shinit_f userinit) nv_putval(ENVNOD,sfstruse(sh.strbuf),NV_RDONLY); } /* increase SHLVL */ - shlvl++; + sh.shlvl++; #if SHOPT_SPAWN { /* @@ -1672,7 +1671,7 @@ void sh_reinit(void) else env_import_attributes(env_init()); /* Increase SHLVL */ - shlvl++; + sh.shlvl++; /* call user init function, if any */ if(sh.userinit) (*sh.userinit)(&sh, 1); @@ -1804,7 +1803,7 @@ static Init_t *nv_init(void) sh.nvfun.last = (char*)&sh; sh.nvfun.nofree = 1; sh.var_base = sh.var_tree = sh_inittree(shtab_variables); - SHLVL->nvalue.ip = &shlvl; + SHLVL->nvalue.lp = &sh.shlvl; ip->IFS_init.hdr.disc = &IFS_disc; ip->PATH_init.disc = &RESTRICTED_disc; ip->PATH_init.nofree = 1; diff --git a/src/cmd/ksh93/tests/variables.sh b/src/cmd/ksh93/tests/variables.sh index 12a797a..5754085 100755 --- a/src/cmd/ksh93/tests/variables.sh +++ b/src/cmd/ksh93/tests/variables.sh @@ -1619,5 +1619,12 @@ got=$(set +x; { "$SHELL" -c ' "(expected status 0, $(printf %q "$exp");" \ "got status $e$( ((e>128)) && print -n /SIG && kill -l "$e"), $(printf %q "$got"))" +# ====== +# exec after unset SHLVL +# https://github.com/ksh93/ksh/issues/788 +{ "$SHELL" -c 'unset SHLVL; exec true'; } 2>/dev/null +(((e=$?)==0)) || err_exit "crash after unsetting SHLVL" \ + "(expected status 0, got status $e$( ((e>128)) && print -n /SIG && kill -l "$e"))" + # ====== exit $((Errors<125?Errors:125)) -- 2.46.2