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authorDenys Vlasenko2018-07-27 12:14:39 +0200
committerDenys Vlasenko2018-07-27 12:14:39 +0200
commit186cf4976768029113cf8438734a65bf2c489c5c (patch)
tree0b2c2a4acad5472d65d87d7274cf91da2152d6b4
parent7c5f18a3bab721cdfa515220ad8d481643aaae23 (diff)
downloadbusybox-186cf4976768029113cf8438734a65bf2c489c5c.zip
busybox-186cf4976768029113cf8438734a65bf2c489c5c.tar.gz
hush: in some cases, expand_on_ifs() relied of uninitialized memory
The n > 0 check to prevent access to the last byte of non-existing argv[-1] wasn't enough. Switched to making sure there are initialized (zero) bytes there. A predictable testcase is rather hard to construct, unfortunately, contents of memory depends on allocator behavior and whatnot. function old new delta o_save_ptr_helper 119 137 +18 expand_on_ifs 345 339 -6 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 1/1 up/down: 18/-6) Total: 12 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--shell/hush.c15
1 files changed, 13 insertions, 2 deletions
diff --git a/shell/hush.c b/shell/hush.c
index 02fb1b5..1ac2db3 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -3069,6 +3069,13 @@ static int o_save_ptr_helper(o_string *o, int n)
o->data = xrealloc(o->data, o->maxlen + 1);
list = (char**)o->data;
memmove(list + n + 0x10, list + n, string_len);
+ /*
+ * expand_on_ifs() has a "previous argv[] ends in IFS?"
+ * check. (grep for -prev-ifs-check-).
+ * Ensure that argv[-1][last] is not garbage
+ * but zero bytes, to save index check there.
+ */
+ list[n + 0x10 - 1] = 0;
o->length += 0x10 * sizeof(list[0]);
} else {
debug_printf_list("list[%d]=%d string_start=%d\n",
@@ -5797,12 +5804,16 @@ static int expand_on_ifs(o_string *output, int n, const char *str)
/* Start new word... but not always! */
/* Case "v=' a'; echo ''$v": we do need to finalize empty word: */
if (output->has_quoted_part
- /* Case "v=' a'; echo $v":
+ /*
+ * Case "v=' a'; echo $v":
* here nothing precedes the space in $v expansion,
* therefore we should not finish the word
* (IOW: if there *is* word to finalize, only then do it):
+ * It's okay if this accesses the byte before first argv[]:
+ * past call to o_save_ptr() cleared it to zero byte
+ * (grep for -prev-ifs-check-).
*/
- || (n > 0 && output->data[output->length - 1])
+ || output->data[output->length - 1]
) {
new_word:
o_addchr(output, '\0');