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Change in dumping of NULL strings

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When dumping a string, adding 2 to its size may overflow a size_t for
external strings, which may not have a header. (Adding 1 is Ok, because
all strings end with a '\0' not included in their size.) The new method
for saving NULL strings code them as a repeated string, using the
reserved index 0.
This commit is contained in:
Roberto I 2025-10-10 15:28:41 -03:00
parent 3347c9d32d
commit 7a92f3f99a
2 changed files with 19 additions and 15 deletions
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22
ldump.c
View File

@ -132,27 +132,31 @@ static void dumpInteger (DumpState *D, lua_Integer x) {
/*
** Dump a String. First dump its "size": size==0 means NULL;
** size==1 is followed by an index and means "reuse saved string with
** that index"; size>=2 is followed by the string contents with real
** size==size-2 and means that string, which will be saved with
** the next available index.
** Dump a String. First dump its "size":
** size==0 is followed by an index and means "reuse saved string with
** that index"; index==0 means NULL.
** size>=1 is followed by the string contents with real size==size-1 and
** means that string, which will be saved with the next available index.
** The real size does not include the ending '\0' (which is not dumped),
** so adding 1 to it cannot overflow a size_t.
*/
static void dumpString (DumpState *D, TString *ts) {
if (ts == NULL)
dumpSize(D, 0);
if (ts == NULL) {
dumpVarint(D, 0); /* will "reuse" NULL */
dumpVarint(D, 0); /* special index for NULL */
}
else {
TValue idx;
int tag = luaH_getstr(D->h, ts, &idx);
if (!tagisempty(tag)) { /* string already saved? */
dumpVarint(D, 1); /* reuse a saved string */
dumpVarint(D, 0); /* reuse a saved string */
dumpVarint(D, l_castS2U(ivalue(&idx))); /* index of saved string */
}
else { /* must write and save the string */
TValue key, value; /* to save the string in the hash */
size_t size;
const char *s = getlstr(ts, size);
dumpSize(D, size + 2);
dumpSize(D, size + 1);
dumpVector(D, s, size + 1); /* include ending '\0' */
D->nstr++; /* one more saved string */
setsvalue(D->L, &key, ts); /* the string is the key */

12
lundump.c
View File

@ -147,20 +147,20 @@ static void loadString (LoadState *S, Proto *p, TString **sl) {
TString *ts;
TValue sv;
size_t size = loadSize(S);
if (size == 0) { /* no string? */
lua_assert(*sl == NULL); /* must be prefilled */
return;
}
else if (size == 1) { /* previously saved string? */
if (size == 0) { /* previously saved string? */
lua_Unsigned idx = loadVarint(S, LUA_MAXUNSIGNED); /* get its index */
TValue stv;
if (idx == 0) { /* no string? */
lua_assert(*sl == NULL); /* must be prefilled */
return;
}
if (novariant(luaH_getint(S->h, l_castU2S(idx), &stv)) != LUA_TSTRING)
error(S, "invalid string index");
*sl = ts = tsvalue(&stv); /* get its value */
luaC_objbarrier(L, p, ts);
return; /* do not save it again */
}
else if ((size -= 2) <= LUAI_MAXSHORTLEN) { /* short string? */
else if ((size -= 1) <= LUAI_MAXSHORTLEN) { /* short string? */
char buff[LUAI_MAXSHORTLEN + 1]; /* extra space for '\0' */
loadVector(S, buff, size + 1); /* load string into buffer */
*sl = ts = luaS_newlstr(L, buff, size); /* create string */