Do not evaluate arithmetic expressions from environment variables at startup

Resolves: #1790549

ksh-2020.0.0-cve-2019-14868.patch

@@ -0,0 +1,78 @@
+diff --git a/src/cmd/ksh93/sh/arith.c b/src/cmd/ksh93/sh/arith.c
+--- a/src/cmd/ksh93/sh/arith.c
++++ b/src/cmd/ksh93/sh/arith.c
+@@ -567,19 +567,32 @@ Sfdouble_t sh_strnum(Shell_t *shp, const char *str, char **ptr, int mode) {
+     char *last;
+ 
+     if (*str == 0) {
+-        if (ptr) *ptr = (char *)str;
+-        return 0;
+-    }
+-    errno = 0;
+-    d = number(str, &last, shp->inarith ? 0 : 10, NULL);
+-    if (*last) {
+-        if (*last != '.' || last[1] != '.') {
+-            d = strval(shp, str, &last, arith, mode);
+-            Varsubscript = true;
++        d = 0.0;
++        last = (char *)str;
++    } else {
++        d = number(str, &last, shp->inarith ? 0 : 10, NULL);
++        if (*last && !shp->inarith && sh_isstate(shp, SH_INIT)) {
++            // This call is to handle "base#value" literals if we're importing untrusted env vars.
++            d = number(str, &last, 0, NULL);
++        }
++        if (*last) {
++            if (sh_isstate(shp, SH_INIT)) {
++                // Initializing means importing untrusted env vars. Since the string does not appear
++                // to be a recognized numeric literal give up. We can't safely call strval() since
++                // that allows arbitrary expressions which would create a security vulnerability.
++                d = 0.0;
++            } else {
++                if (*last != '.' || last[1] != '.') {
++                    d = strval(shp, str, &last, arith, mode);
++                    Varsubscript = true;
++                }
++                if (!ptr && *last && mode > 0) {
++                    errormsg(SH_DICT, ERROR_exit(1), e_lexbadchar, *last, str);
++                }
++            }
++        } else if (d == 0.0 && *str == '-') {
++            d = -0.0;
+         }
+-        if (!ptr && *last && mode > 0) errormsg(SH_DICT, ERROR_exit(1), e_lexbadchar, *last, str);
+-    } else if (!d && *str == '-') {
+-        d = -0.0;
+     }
+     if (ptr) *ptr = last;
+     return d;
+diff --git a/src/cmd/ksh93/tests/subshell.sh b/src/cmd/ksh93/tests/subshell.sh
+--- a/src/cmd/ksh93/tests/subshell.sh
++++ b/src/cmd/ksh93/tests/subshell.sh
+@@ -856,3 +856,26 @@ for exp in 65535 65536
+ do    got=$($SHELL -c 'x=$(printf "%.*c" '$exp' x); print ${#x}' 2>&1)
+     [[ $got == $exp ]] || log_error "large command substitution failed" "$exp" "$got"
+ done
++
++# ==========
++# Verify that importing untrusted env vars does not allow evaluating arbitrary expressions but does
++# recognize all integer literals recognized by ksh.
++expect=8
++actual=$(env SHLVL='7' $SHELL -c 'echo $SHLVL')
++[[ $actual == $expect ]] || log_error "decimal int literal not recognized" "$expect" "$actual"
++
++expect=14
++actual=$(env SHLVL='013' $SHELL -c 'echo $SHLVL')
++[[ $actual == $expect ]] || log_error "leading zeros int literal not recognized" "$expect" "$actual"
++
++expect=4
++actual=$(env SHLVL='2#11' $SHELL -c 'echo $SHLVL')
++[[ $actual == $expect ]] || log_error "base#value int literal not recognized" "$expect" "$actual"
++
++expect=12
++actual=$(env SHLVL='16#B' $SHELL -c 'echo $SHLVL')
++[[ $actual == $expect ]] || log_error "base#value int literal not recognized" "$expect" "$actual"
++
++expect=1
++actual=$(env SHLVL="2#11+x[\$($bin_echo DANGER WILL ROBINSON >&2)0]" $SHELL -c 'echo $SHLVL')
++[[ $actual == $expect ]] || log_error "expression allowed on env var import" "$expect" "$actual"

ksh.spec

@@ -3,7 +3,7 @@ Summary:      The Original ATT Korn Shell
 URL:          http://www.kornshell.com/
 License:      EPL
 Version:      2020.0.0
-Release:      2%{?dist}
+Release:      3%{?dist}
 # We are upgrading from ksh-20120801-250, so set epoch.
 Epoch:        1
 Source0:      https://github.com/att/ast/releases/download/%{version}/%{name}-%{version}.tar.gz
@@ -11,6 +11,8 @@ Source1:      kshcomp.conf
 Source2:      kshrc.rhs
 Source3:      dotkshrc
 
+Patch1: ksh-2020.0.0-cve-2019-14868.patch
+
 Provides: /bin/ksh
 
 BuildRequires:  meson
@@ -32,7 +34,7 @@ KornShell is a shell programming language, which is upward compatible
 with "sh" (the Bourne Shell).
 
 %prep
-%autosetup -n %{name}-%{version}
+%autosetup -n %{name}-%{version} -p1
 
 %build
 %meson -Dbuild-api-tests=false
@@ -108,6 +110,10 @@ done
 %config(noreplace) %{_sysconfdir}/binfmt.d/kshcomp.conf
 
 %changelog
+* Fri Feb 07 2020 Siteshwar Vashisht <svashisht@redhat.com> - 1:2020.0.0-3
+- Do not evaluate arithmetic expressions from environment variables at startup
+  Resolves: #1790549
+
 * Wed Jan 29 2020 Fedora Release Engineering <releng@fedoraproject.org> - 1:2020.0.0-2
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_32_Mass_Rebuild