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isolation: Initially Keep CAP_SETFCAP if running as UID 0 in non-init

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If pasta spawns a child process while running as UID 0, which is only
allowed from a non-init namespace, we need to keep CAP_SETFCAP before
pasta_start_ns() is called: otherwise, starting from Linux 5.12, we
won't be able to update /proc/self/uid_map with the intended mapping
(from 0 to 0). See user_namespaces(7).

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Stefano Brivio 2023-05-21 15:03:31 +02:00
parent b0e450aa85
commit 770d1a4502
1 changed files with 14 additions and 3 deletions
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17
isolation.c
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@ -177,6 +177,8 @@ static void clamp_caps(void)
*/ */
void isolate_initial(void) void isolate_initial(void)
{ {
uint64_t keep;
/* We want to keep CAP_NET_BIND_SERVICE in the initial /* We want to keep CAP_NET_BIND_SERVICE in the initial
* namespace if we have it, so that we can forward low ports * namespace if we have it, so that we can forward low ports
* into the guest/namespace * into the guest/namespace
@ -193,9 +195,18 @@ void isolate_initial(void)
* further capabilites in isolate_user() and * further capabilites in isolate_user() and
* isolate_prefork(). * isolate_prefork().
*/ */
drop_caps_ep_except(BIT(CAP_NET_BIND_SERVICE) | keep = BIT(CAP_NET_BIND_SERVICE) | BIT(CAP_SETUID) | BIT(CAP_SETGID) |
BIT(CAP_SETUID) | BIT(CAP_SETGID) | BIT(CAP_SYS_ADMIN) | BIT(CAP_NET_ADMIN);
BIT(CAP_SYS_ADMIN) | BIT(CAP_NET_ADMIN));
/* Since Linux 5.12, if we want to update /proc/self/uid_map to create
* a mapping from UID 0, which only happens with pasta spawning a child
* from a non-init user namespace (pasta can't run as root), we need to
* retain CAP_SETFCAP too.
*/
if (!ns_is_init() && !geteuid())
keep |= BIT(CAP_SETFCAP);
drop_caps_ep_except(keep);
} }
/** /**