shell: avoid segfault on ${0::0/0~09J}. Closes 15216

function                                             old     new   delta
evaluate_string                                     1011    1053     +42

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 35 insertions, 4 deletions

diff --git a/shell/math.c b/shell/math.c
index 76d22c9bd..727c29467 100644
--- a/shell/math.c
+++ b/shell/math.c
@@ -577,6 +577,28 @@ 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
 evaluate_string(arith_state_t *math_state, const char *expr)
 {
@@ -584,10 +606,12 @@ 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 */
@@ -652,6 +676,13 @@ 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;
 //bb_error_msg("val:%lld", numstackptr->val);
                         if (errno)
                                 numstackptr->val = 0; /* bash compat */