ash: make ${v:N:M} more robust for very large M by clamping to MIN/MAX_INT

Before this patch, "${v:2:0x100000001}" = "${v:2:1}",
and similarly, constructs like "${v:2:9999999999}" may give wrong result
due to int overflows.

function                                             old     new   delta
substr_atoi                                            -      43     +43

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

1 files changed, 25 insertions, 13 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 83a8e77f9..a7f330c11 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -5780,6 +5780,26 @@ ash_arith(const char *s)
         return result;
 }
 #endif
+#if BASH_SUBSTR
+# if ENABLE_FEATURE_SH_MATH
+static int substr_atoi(const char *s)
+{
+        arith_t t = ash_arith(s);
+        if (sizeof(t) > sizeof(int)) {
+                /* clamp very large or very large negative nums for ${v:N:M}:
+                 * else "${v:0:0x100000001}" would work as "${v:0:1}"
+                 */
+                if (t > INT_MAX)
+                        t = INT_MAX;
+                if (t < INT_MIN)
+                        t = INT_MIN;
+        }
+        return t;
+}
+# else
+#  define substr_atoi(s) number(s)
+# endif
+#endif
 
 /*
  * expandarg flags
@@ -6816,13 +6836,10 @@ subevalvar(char *p, char *varname, int strloc, int subtype,
 
                 loc = str = stackblock() + strloc;
 
-# if !ENABLE_FEATURE_SH_MATH
-#  define ash_arith number
-# endif
                 /* Read POS in ${var:POS:LEN} */
                 colon = strchr(loc, ':');
                 if (colon) *colon = '\0';
-                pos = ash_arith(loc);
+                pos = substr_atoi(loc);
                 if (colon) *colon = ':';
 
                 /* Read LEN in ${var:POS:LEN} */
@@ -6830,7 +6847,6 @@ subevalvar(char *p, char *varname, int strloc, int subtype,
                 /* *loc != '\0', guaranteed by parser */
                 if (quotes) {
                         char *ptr;
-
                         /* Adjust the length by the number of escapes */
                         for (ptr = startp; ptr < (str - 1); ptr++) {
                                 if ((unsigned char)*ptr == CTLESC) {
@@ -6842,19 +6858,15 @@ subevalvar(char *p, char *varname, int strloc, int subtype,
                 orig_len = len;
                 if (*loc++ == ':') {
                         /* ${var::LEN} */
-                        len = ash_arith(loc);
+                        len = substr_atoi(loc);
                 } else {
                         /* Skip POS in ${var:POS:LEN} */
                         len = orig_len;
-                        while (*loc && *loc != ':') {
+                        while (*loc && *loc != ':')
                                 loc++;
-                        }
-                        if (*loc++ == ':') {
-                                len = ash_arith(loc);
-                        }
+                        if (*loc++ == ':')
+                                len = substr_atoi(loc);
                 }
-#  undef ash_arith
-
                 if (pos < 0) {
                         /* ${VAR:$((-n)):l} starts n chars from the end */
                         pos = orig_len + pos;