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lua: add flex array field to TString type

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Linux 6.10+ with CONFIG_FORTIFY_SOURCE notices memcpy() accessing past
the end of TString, because it has no indication that there there may be
an additional allocation there.

There's no appropriate upstream change for this (ancient) version of
Lua, so this is the narrowest change I could come up with to add a flex
array field to the end of TString to satisfy the check. It's loosely
based on changes from lua/lua@ca41b43f and lua/lua@9514abc2.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #16541
Closes #16583
This commit is contained in:
Rob Norris 2024-10-01 03:30:03 +10:00 committed by Tony Hutter
parent 2bd540d273
commit 4adc97ae15
4 changed files with 15 additions and 12 deletions
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21
module/lua/lobject.h
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@ -404,19 +404,22 @@ typedef TValue *StkId; /* index to stack elements */
/* /*
** Header for string value; string bytes follow the end of this structure ** Header for string value; string bytes follow the end of this structure
*/ */
typedef union TString { typedef struct TString {
L_Umaxalign dummy; /* ensures maximum alignment for strings */ union {
struct { L_Umaxalign dummy; /* ensures maximum alignment for strings */
CommonHeader; struct {
lu_byte extra; /* reserved words for short strings; "has hash" for longs */ CommonHeader;
unsigned int hash; lu_byte extra; /* reserved words for short strings; "has hash" for longs */
size_t len; /* number of characters in string */ unsigned int hash;
} tsv; size_t len; /* number of characters in string */
} tsv;
};
char contents[];
} TString; } TString;
/* get the actual string (array of bytes) from a TString */ /* get the actual string (array of bytes) from a TString */
#define getstr(ts) cast(const char *, (ts) + 1) #define getstr(ts) ((ts)->contents)
/* get the actual string (array of bytes) from a Lua value */ /* get the actual string (array of bytes) from a Lua value */
#define svalue(o) getstr(rawtsvalue(o)) #define svalue(o) getstr(rawtsvalue(o))

2
module/lua/lstate.h
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@ -185,7 +185,7 @@ struct lua_State {
*/ */
union GCObject { union GCObject {
GCheader gch; /* common header */ GCheader gch; /* common header */
union TString ts; struct TString ts;
union Udata u; union Udata u;
union Closure cl; union Closure cl;
struct Table h; struct Table h;

2
module/lua/lstring.c
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@ -103,7 +103,7 @@ static TString *createstrobj (lua_State *L, const char *str, size_t l,
ts->tsv.len = l; ts->tsv.len = l;
ts->tsv.hash = h; ts->tsv.hash = h;
ts->tsv.extra = 0; ts->tsv.extra = 0;
sbuf = (char *)(TString *)(ts + 1); sbuf = ts->contents;
memcpy(sbuf, str, l*sizeof(char)); memcpy(sbuf, str, l*sizeof(char));
sbuf[l] = '\0'; /* ending 0 */ sbuf[l] = '\0'; /* ending 0 */
return ts; return ts;

2
module/lua/lstring.h
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@ -12,7 +12,7 @@
#include "lstate.h" #include "lstate.h"
#define sizestring(s) (sizeof(union TString)+((s)->len+1)*sizeof(char)) #define sizestring(s) (sizeof(struct TString)+((s)->len+1)*sizeof(char))
#define sizeudata(u) (sizeof(union Udata)+(u)->len) #define sizeudata(u) (sizeof(union Udata)+(u)->len)