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90 lines
3.7 KiB
90 lines
3.7 KiB
From c7de8b641266bac7c77942239ac659edfee9ecd2 Mon Sep 17 00:00:00 2001
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From: Kurtis Rader <krader@skepticism.us>
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Date: Thu, 12 Dec 2019 18:46:50 -0800
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Subject: [PATCH] Harden env var imports
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---
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src/cmd/ksh93/sh/arith.c | 37 ++++++++++++++++++++++-----------
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src/cmd/ksh93/tests/subshell.sh | 23 ++++++++++++++++++++
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diff --git a/src/cmd/ksh93/sh/arith.c b/src/cmd/ksh93/sh/arith.c
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index 30b3067590a2..8e68cbdc868a 100644
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--- a/src/cmd/ksh93/sh/arith.c
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+++ b/src/cmd/ksh93/sh/arith.c
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@@ -567,19 +567,32 @@ Sfdouble_t sh_strnum(Shell_t *shp, const char *str, char **ptr, int mode) {
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char *last;
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if (*str == 0) {
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- if (ptr) *ptr = (char *)str;
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- return 0;
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- }
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- errno = 0;
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- d = number(str, &last, shp->inarith ? 0 : 10, NULL);
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- if (*last) {
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- if (*last != '.' || last[1] != '.') {
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- d = strval(shp, str, &last, arith, mode);
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- Varsubscript = true;
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+ d = 0.0;
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+ last = (char *)str;
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+ } else {
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+ d = number(str, &last, shp->inarith ? 0 : 10, NULL);
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+ if (*last && !shp->inarith && sh_isstate(shp, SH_INIT)) {
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+ // This call is to handle "base#value" literals if we're importing untrusted env vars.
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+ d = number(str, &last, 0, NULL);
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+ }
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+ if (*last) {
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+ if (sh_isstate(shp, SH_INIT)) {
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+ // Initializing means importing untrusted env vars. Since the string does not appear
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+ // to be a recognized numeric literal give up. We can't safely call strval() since
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+ // that allows arbitrary expressions which would create a security vulnerability.
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+ d = 0.0;
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+ } else {
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+ if (*last != '.' || last[1] != '.') {
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+ d = strval(shp, str, &last, arith, mode);
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+ Varsubscript = true;
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+ }
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+ if (!ptr && *last && mode > 0) {
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+ errormsg(SH_DICT, ERROR_exit(1), e_lexbadchar, *last, str);
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+ }
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+ }
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+ } else if (d == 0.0 && *str == '-') {
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+ d = -0.0;
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}
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- if (!ptr && *last && mode > 0) errormsg(SH_DICT, ERROR_exit(1), e_lexbadchar, *last, str);
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- } else if (!d && *str == '-') {
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- d = -0.0;
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}
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if (ptr) *ptr = last;
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return d;
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diff --git a/src/cmd/ksh93/tests/subshell.sh b/src/cmd/ksh93/tests/subshell.sh
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index b63a8051ed5c..3faba475d6de 100644
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--- a/src/cmd/ksh93/tests/subshell.sh
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+++ b/src/cmd/ksh93/tests/subshell.sh
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@@ -856,3 +856,26 @@ for exp in 65535 65536
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do got=$($SHELL -c 'x=$(printf "%.*c" '$exp' x); print ${#x}' 2>&1)
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[[ $got == $exp ]] || log_error "large command substitution failed" "$exp" "$got"
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done
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+
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+# ==========
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+# Verify that importing untrusted env vars does not allow evaluating arbitrary expressions but does
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+# recognize all integer literals recognized by ksh.
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+expect=8
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+actual=$(env SHLVL='7' $SHELL -c 'echo $SHLVL')
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+[[ $actual == $expect ]] || log_error "decimal int literal not recognized" "$expect" "$actual"
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+
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+expect=14
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+actual=$(env SHLVL='013' $SHELL -c 'echo $SHLVL')
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+[[ $actual == $expect ]] || log_error "leading zeros int literal not recognized" "$expect" "$actual"
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+
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+expect=4
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+actual=$(env SHLVL='2#11' $SHELL -c 'echo $SHLVL')
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+[[ $actual == $expect ]] || log_error "base#value int literal not recognized" "$expect" "$actual"
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+
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+expect=12
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+actual=$(env SHLVL='16#B' $SHELL -c 'echo $SHLVL')
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+[[ $actual == $expect ]] || log_error "base#value int literal not recognized" "$expect" "$actual"
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+
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+expect=1
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+actual=$(env SHLVL="2#11+x[\$($bin_echo DANGER WILL ROBINSON >&2)0]" $SHELL -c 'echo $SHLVL')
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+[[ $actual == $expect ]] || log_error "expression allowed on env var import" "$expect" "$actual"
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