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service_manager: reorder permission checks for find 

Reorder the find permission checks. This avoids generating misleading
SELinux denials when a service doesn't exist, or when a service is
prohibited to isolated apps.

The original reason for structuring the code this way is explained
in https://android-review.googlesource.com/#/c/100530/4/cmds/servicemanager/service_manager.c@172
The concern at the time was to avoid leaking a situation where
a caller could probe for the existance of a service. This turns out
to be unnecessary. The same return value is used for both a
permission denied and a service not found. The only side effect
is the generation of an SELinux audit log, which likely won't be
accessible to the calling application.

Change-Id: I9760e1821ed16102fa5f9bec07f8c34944565be9
This commit is contained in:
Nick Kralevich 2015-03-05 10:58:40 -08:00
parent 9d68ed0ecd
commit b27bbd18bb
1 changed files with 16 additions and 18 deletions
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34
cmds/servicemanager/service_manager.c
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@ -169,28 +169,26 @@ uint16_t svcmgr_id[] = {
uint32_t do_find_service(struct binder_state *bs, const uint16_t *s, size_t len, uid_t uid, pid_t spid)
{
struct svcinfo *si;
struct svcinfo *si = find_svc(s, len);
if (!si || !si->handle) {
return 0;
}
if (!si->allow_isolated) {
// If this service doesn't allow access from isolated processes,
// then check the uid to see if it is isolated.
uid_t appid = uid % AID_USER;
if (appid >= AID_ISOLATED_START && appid <= AID_ISOLATED_END) {
return 0;
}
}
if (!svc_can_find(s, len, spid)) {
ALOGE("find_service('%s') uid=%d - PERMISSION DENIED\n",
str8(s, len), uid);
return 0;
}
si = find_svc(s, len);
//ALOGI("check_service('%s') handle = %x\n", str8(s, len), si ? si->handle : 0);
if (si && si->handle) {
if (!si->allow_isolated) {
// If this service doesn't allow access from isolated processes,
// then check the uid to see if it is isolated.
uid_t appid = uid % AID_USER;
if (appid >= AID_ISOLATED_START && appid <= AID_ISOLATED_END) {
return 0;
}
}
return si->handle;
} else {
return 0;
}
return si->handle;
}
int do_add_service(struct binder_state *bs,