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kernel: fix Abind cyclic reference and mounthead leaks (thanks Alex Musolino)

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The Abind case in namec() needs to cunique() the chan
before attaching the umh mount head pointer onto it.

This is because we cannot give a reference to the mount
head to any of the mh->mount...->to channels, as they
will never go away until the mount head goes away.
This is a cyclic reference.

This could be reproduced with:

	@{rfork n; mount -a '#s/boot' /mnt/root; bind /mnt/root /}

Also, fix memory leaks around cunique(), which can
error, leaking the mount head we got from domount().

Move the umh != nil check inside cunique().
This commit is contained in:
cinap_lenrek 2020-08-23 05:07:30 +02:00
parent 951a71012f
commit 603d9812a7
1 changed files with 17 additions and 12 deletions
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29
sys/src/9/port/chan.c
View file

@ -556,6 +556,12 @@ cunique(Chan *c)
c = nc;
}
if(c->umh != nil){ //BUG
print("cunique umh != nil from %#p\n", getcallerpc(&c));
putmhead(c->umh);
c->umh = nil;
}
return c;
}
@ -1094,11 +1100,6 @@ walk(Chan **cp, char **names, int nnames, int nomount, int *nerror)
}
putmhead(mh);
c = cunique(c);
if(c->umh != nil){ //BUG
print("walk umh\n");
putmhead(c->umh);
c->umh = nil;
}
pathclose(c->path);
c->path = path;
@ -1410,8 +1411,13 @@ namec(char *aname, int amode, int omode, ulong perm)
m = nil;
if(!nomount)
domount(&c, &m, nil);
putmhead(c->umh);
if(waserror()){
putmhead(m);
nexterror();
}
c = cunique(c);
c->umh = m;
poperror();
break;
case Aaccess:
@ -1428,9 +1434,13 @@ namec(char *aname, int amode, int omode, ulong perm)
m = nil;
if(!nomount)
domount(&c, &m, &path);
if(waserror()){
putmhead(m);
nexterror();
}
/* our own copy to open or remove */
c = cunique(c);
poperror();
/* now it's our copy anyway, we can put the name back */
pathclose(c->path);
@ -1448,11 +1458,6 @@ namec(char *aname, int amode, int omode, ulong perm)
case Aopen:
case Acreate:
if(c->umh != nil){
print("cunique umh Open\n");
putmhead(c->umh);
c->umh = nil;
}
/* only save the mount head if it's a multiple element union */
if(m != nil && m->mount != nil && m->mount->next != nil)
c->umh = m;