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From c7de8b641266bac7c77942239ac659edfee9ecd2 Mon Sep 17 00:00:00 2001
From: Kurtis Rader <krader@skepticism.us>
Date: Thu, 12 Dec 2019 18:46:50 -0800
Subject: [PATCH] Harden env var imports
---
src/cmd/ksh93/sh/arith.c | 37 ++++++++++++++++++++++-----------
src/cmd/ksh93/tests/subshell.sh | 23 ++++++++++++++++++++
diff --git a/src/cmd/ksh93/sh/arith.c b/src/cmd/ksh93/sh/arith.c
index 30b3067590a2..8e68cbdc868a 100644
--- 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
index b63a8051ed5c..3faba475d6de 100644
--- 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"
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