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From c18ebf861528ef24958dd99a146482d2a40014c7 Mon Sep 17 00:00:00 2001
From: Denys Vlasenko <vda.linux@googlemail.com>
Date: Mon, 12 Jun 2023 17:48:47 +0200
Subject: [PATCH] shell: avoid segfault on ${0::0/0~09J}. Closes 15216
function old new delta
evaluate_string 1011 1053 +42
CVE: CVE-2022-48174
Upstream-Status: Backport [d417193cf37ca1005830d7e16f5fa7e1d8a44209]
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
---
shell/math.c | 39 +++++++++++++++++++++++++++++++++++----
1 file changed, 35 insertions(+), 4 deletions(-)
diff --git a/shell/math.c b/shell/math.c
index af1ab55c0..79824e81f 100644
--- a/shell/math.c
+++ b/shell/math.c
@@ -578,6 +578,28 @@ static arith_t strto_arith_t(const char *nptr, char **endptr)
# endif
#endif
+//TODO: much better estimation than expr_len/2? Such as:
+//static unsigned estimate_nums_and_names(const char *expr)
+//{
+// unsigned count = 0;
+// while (*(expr = skip_whitespace(expr)) != '\0') {
+// const char *p;
+// if (isdigit(*expr)) {
+// while (isdigit(*++expr))
+// continue;
+// count++;
+// continue;
+// }
+// p = endofname(expr);
+// if (p != expr) {
+// expr = p;
+// count++;
+// continue;
+// }
+// }
+// return count;
+//}
+
static arith_t FAST_FUNC
evaluate_string(arith_state_t *math_state, const char *expr)
{
@@ -585,10 +607,12 @@ evaluate_string(arith_state_t *math_state, const char *expr)
const char *errmsg;
const char *start_expr = expr = skip_whitespace(expr);
unsigned expr_len = strlen(expr) + 2;
- /* Stack of integers */
- /* The proof that there can be no more than strlen(startbuf)/2+1
- * integers in any given correct or incorrect expression
- * is left as an exercise to the reader. */
+ /* Stack of integers/names */
+ /* There can be no more than strlen(startbuf)/2+1
+ * integers/names in any given correct or incorrect expression.
+ * (modulo "09v09v09v09v09v" case,
+ * but we have code to detect that early)
+ */
var_or_num_t *const numstack = alloca((expr_len / 2) * sizeof(numstack[0]));
var_or_num_t *numstackptr = numstack;
/* Stack of operator tokens */
@@ -657,6 +681,13 @@ evaluate_string(arith_state_t *math_state, const char *expr)
numstackptr->var = NULL;
errno = 0;
numstackptr->val = strto_arith_t(expr, (char**) &expr);
+ /* A number can't be followed by another number, or a variable name.
+ * We'd catch this later anyway, but this would require numstack[]
+ * to be twice as deep to handle strings where _every_ char is
+ * a new number or name. Example: 09v09v09v09v09v09v09v09v09v
+ */
+ if (isalnum(*expr) || *expr == '_')
+ goto err;
if (errno)
numstackptr->val = 0; /* bash compat */
goto num;
--
2.40.1
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