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devcap: timeout capabilities after a minute, fix memory leak, paranoia

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the manpage states that capabilities time out after a minute,
so we add ticks field into the Caphash struct and record the
time when the capability was inserted. freeing old capabilities
is handled in trimcaps(), which makes room for one extra cap
and frees timed out ones.

we also limit the capuse write size to less than 1024 bytes to
prevent denial of service as we have to copy the user buffer.
(memory exhaustion).

we have to check the from user *before* attempting to remove
the capability! the wrong user shouldnt be able to change any
state. this fixes the memory leak of the caphash.

do the hash comparsion with tsmemcmp(), avoiding timing
side channels.

allocate the capabilities in secret memory pool to prevent
debugger access.
This commit is contained in:
cinap_lenrek 2016-09-07 21:14:23 +02:00
parent 76daf9f863
commit bfd8098b8d
1 changed files with 36 additions and 37 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

73
sys/src/9/port/devcap.c
View file

@ -11,6 +11,7 @@ enum
{
Hashlen= SHA1dlen,
Maxhash= 256,
Timeout= 60, /* seconds */
};
/*
@ -21,11 +22,11 @@ typedef struct Caphash Caphash;
struct Caphash
{
Caphash *next;
char hash[Hashlen];
ulong ticks;
ulong ticks;
char hash[Hashlen];
};
struct
static struct
{
QLock;
Caphash *first;
@ -104,19 +105,19 @@ capopen(Chan *c, int omode)
return c;
}
/*
static char*
hashstr(uchar *hash)
static void
trimcaps(void)
{
static char buf[2*Hashlen+1];
int i;
Caphash *t;
for(i = 0; i < Hashlen; i++)
sprint(buf+2*i, "%2.2ux", hash[i]);
buf[2*Hashlen] = 0;
return buf;
while((t = capalloc.first) != nil){
if(capalloc.nhash < Maxhash && TK2SEC(MACHP(0)->ticks - t->ticks) < Timeout)
break;
capalloc.nhash--;
capalloc.first = t->next;
secfree(t);
}
}
*/
static Caphash*
remcap(uchar *hash)
@ -125,10 +126,13 @@ remcap(uchar *hash)
qlock(&capalloc);
/* timeout old caps */
trimcaps();
/* find the matching capability */
for(l = &capalloc.first; *l != nil;){
t = *l;
if(memcmp(hash, t->hash, Hashlen) == 0)
if(tsmemcmp(hash, t->hash, Hashlen) == 0)
break;
l = &t->next;
}
@ -146,24 +150,17 @@ remcap(uchar *hash)
static void
addcap(uchar *hash)
{
Caphash *p, *t, **l;
Caphash *p, **l;
p = smalloc(sizeof *p);
p = secalloc(sizeof *p);
memmove(p->hash, hash, Hashlen);
p->next = nil;
p->ticks = m->ticks;
p->ticks = MACHP(0)->ticks;
qlock(&capalloc);
/* trim extras */
while(capalloc.nhash >= Maxhash){
t = capalloc.first;
if(t == nil)
panic("addcap");
capalloc.first = t->next;
free(t);
capalloc.nhash--;
}
/* make room for one extra */
trimcaps();
/* add new one */
for(l = &capalloc.first; *l != nil; l = &(*l)->next)
@ -213,13 +210,14 @@ capwrite(Chan *c, void *va, long n, vlong)
break;
case Quse:
if((ulong)n >= 1024)
error(Etoobig);
/* copy key to avoid a fault in hmac_xx */
cp = nil;
cp = secalloc(n+1);
if(waserror()){
free(cp);
secfree(cp);
nexterror();
}
cp = smalloc(n+1);
memmove(cp, va, n);
cp[n] = 0;
@ -231,12 +229,6 @@ capwrite(Chan *c, void *va, long n, vlong)
hmac_sha1((uchar*)from, strlen(from), (uchar*)key, strlen(key), hash, nil);
p = remcap(hash);
if(p == nil){
snprint(err, sizeof err, "invalid capability %s@%s", from, key);
error(err);
}
/* if a from user is supplied, make sure it matches */
to = strchr(from, '@');
if(to == nil){
@ -247,12 +239,18 @@ capwrite(Chan *c, void *va, long n, vlong)
error("capability must match user");
}
p = remcap(hash);
if(p == nil){
snprint(err, sizeof err, "invalid capability %s@%s", from, key);
error(err);
}
secfree(p);
/* set user id */
kstrdup(&up->user, to);
up->basepri = PriNormal;
free(p);
free(cp);
secfree(cp);
poperror();
break;
@ -260,6 +258,7 @@ capwrite(Chan *c, void *va, long n, vlong)
error(Eperm);
break;
}
memset(hash, 0, Hashlen);
return n;
}