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lib9/fmt: avoid racy access to installed fmt formats

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This commit is contained in:
Russ Cox 2020-01-13 11:41:37 -05:00
parent d96e9e5dc3
commit 7ba9f9467d
4 changed files with 55 additions and 22 deletions
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35
src/lib9/fmt/fmt.c
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@ -72,7 +72,7 @@ static Convfmt knownfmt[] = {
int (*fmtdoquote)(int);
/*
* __fmtlock() must be set
* __fmtwlock() must be set
*/
static int
__fmtinstall(int c, Fmts f)
@ -106,34 +106,43 @@ fmtinstall(int c, int (*f)(Fmt*))
{
int ret;
__fmtlock();
__fmtwlock();
ret = __fmtinstall(c, f);
__fmtunlock();
__fmtwunlock();
return ret;
}
static Fmts
fmtfmt(int c)
{
Convfmt *p, *ep;
Convfmt *p, *ep, *kp;
/* conflict-free check - common case */
__fmtrlock();
ep = &fmtalloc.fmt[fmtalloc.nfmt];
for(p=fmtalloc.fmt; p<ep; p++)
if(p->c == c){
while(p->fmt == nil) /* loop until value is updated */
;
__fmtrunlock();
return p->fmt;
}
__fmtrunlock();
/* is this a predefined format char? */
__fmtlock();
for(p=knownfmt; p->c; p++)
if(p->c == c){
__fmtinstall(p->c, p->fmt);
__fmtunlock();
return p->fmt;
for(kp=knownfmt; kp->c; kp++){
if(kp->c == c){
__fmtwlock();
/* double-check fmtinstall didn't happen */
for(p=fmtalloc.fmt; p<ep; p++){
if(p->c == c){
__fmtwunlock();
return p->fmt;
}
}
__fmtinstall(kp->c, kp->fmt);
__fmtwunlock();
return kp->fmt;
}
__fmtunlock();
}
return __badfmt;
}