diff options
| author | Xiang Mei (Microsoft) <xmei5@asu.edu> | 2026-07-29 20:06:21 +0000 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-08-04 16:29:51 -0700 |
| commit | 1a930d5734b77ceb0813bb7ecf99d1a89fbe0164 (patch) | |
| tree | 1f59152dc9622d9c47ac36969bbab5791264d306 | |
| parent | 95a390ce6aee1a3927523d5221d290a71b514f7e (diff) | |
macvlan: require init-userns CAP_NET_ADMIN to raise bc_queue_len
IFLA_MACVLAN_BC_QUEUE_LEN accepts any u32 and becomes
port->bc_queue_len_used, the only bound on port->bc_queue. rtnetlink checks
CAP_NET_ADMIN against the target netns only, so a user who unshares a
user+net namespace, creates a veth and puts a macvlan on it can set the
backlog to 0xffffffff and flood broadcast frames until the host dies:
Out of memory: Killed process 141 (su) UID:0
Kernel panic - not syncing: System is deadlocked on memory
Call Trace:
vpanic (kernel/panic.c:650)
panic (kernel/panic.c:787)
out_of_memory (mm/oom_kill.c:1166)
__alloc_frozen_pages_noprof (mm/page_alloc.c:4914)
alloc_pages_mpol (mm/mempolicy.c:2490)
folio_alloc_noprof (mm/mempolicy.c:2591)
filemap_fault (mm/filemap.c:3565)
A fixed upper bound does not work. Deployments carrying 600-800 real-time
audio streams run bc_queue_len=100000, and no constant serves both cases:
the queue counts skbs, not bytes, and the frame size is attacker-chosen too
(up to ETH_MAX_MTU on a veth the caller creates).
Gate the elevated range on CAP_NET_ADMIN in the initial user namespace
instead. A backlog of that size is a host-wide tuning decision, and an
unprivileged owner of a namespace it created itself should not be able to
make it; privileged configurations keep working unchanged..
Cc: stable+noautosel@kernel.org # local DoS by userns are a dime a dozen
Reported-by: AutonomousCodeSecurity@microsoft.com
Link: https://lore.kernel.org/r/20260706212556.3199234-1-xmei5@asu.edu
Signed-off-by: Xiang Mei (Microsoft) <xmei5@asu.edu>
Link: https://patch.msgid.link/20260729200621.2521588-1-xmei5@asu.edu
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
| -rw-r--r-- | drivers/net/macvlan.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c index 9a4bc99dbf53..42169f3614c4 100644 --- a/drivers/net/macvlan.c +++ b/drivers/net/macvlan.c @@ -1339,6 +1339,15 @@ static int macvlan_validate(struct nlattr *tb[], struct nlattr *data[], if (!data) return 0; + if (data[IFLA_MACVLAN_BC_QUEUE_LEN] && + nla_get_u32(data[IFLA_MACVLAN_BC_QUEUE_LEN]) > + MACVLAN_DEFAULT_BC_QUEUE_LEN && + !capable(CAP_NET_ADMIN)) { + NL_SET_ERR_MSG_ATTR(extack, data[IFLA_MACVLAN_BC_QUEUE_LEN], + "bc_queue_len above the default requires CAP_NET_ADMIN in the initial user namespace"); + return -EPERM; + } + if (data[IFLA_MACVLAN_FLAGS] && nla_get_u16(data[IFLA_MACVLAN_FLAGS]) & ~(MACVLAN_FLAG_NOPROMISC | MACVLAN_FLAG_NODST)) |