nfsd_nl_listener_set_doit() matches each requested listener against the
existing set. The nested loop that does this is O(N * M), where N is the
requested count and M is the existing count. The loop runs under sv_lock
with bottom halves disabled. A userland request with a very large listener
list can therefore spin in atomic context for a long time.
Reject a request that carries more than NFSD_NL_LISTENER_MAX (1024)
entries. The check goes in nfsd_nl_validate_listeners(), before the code
takes any lock. The limit is far above any realistic configuration.
This patch does not cap M. Only the message size bounded N; real sockets
bound M. A listener_set result set is the requested set, so that path also
holds M at the cap, but __write_ports_addxprt() adds two listeners per call
and removes none, so repeated calls can push M past it. The worst case
under sv_lock is therefore 1024 * M, plus 1024 nla_parse_nested() calls.
Both interfaces require CAP_NET_ADMIN.
Fixes: 16a471177496 ("NFSD: add listener-{set,get} netlink command")
Assisted-by: LLM
Signed-off-by: Jeff Layton <[email protected]>
---
fs/nfsd/nfsctl.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 5331b89c4281..b6f4d66f612a 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1995,21 +1995,22 @@ int nfsd_nl_version_get_doit(struct sk_buff *skb,
struct genl_info *info)
return err;
}
+/* Upper bound on the number of listeners a single request may carry. */
+#define NFSD_NL_LISTENER_MAX 1024
+
/**
* nfsd_nl_validate_listeners - sanity-check the listener list from userland
* @info: netlink metadata and command arguments
*
- * Walk every NFSD_A_SERVER_SOCK_ADDR attribute and confirm that each entry
- * is well-formed: it parses against the policy, carries both an address and
- * a transport name, and the address is long enough for its family. Doing
- * this up front lets the callers below assume every entry is valid and
- * guarantees we make no changes when the request is malformed.
+ * Walk every NFSD_A_SERVER_SOCK_ADDR attribute and confirm that the list is
+ * not oversized and that each entry is well-formed.
*
* Return: 0 if every entry is valid, or a negative errno otherwise.
*/
static int nfsd_nl_validate_listeners(struct genl_info *info)
{
const struct nlattr *attr;
+ unsigned int count = 0;
int rem;
nlmsg_for_each_attr_type(attr, NFSD_A_SERVER_SOCK_ADDR, info->nlhdr,
@@ -2018,6 +2019,11 @@ static int nfsd_nl_validate_listeners(struct genl_info
*info)
struct sockaddr *sa;
int err;
+ if (++count > NFSD_NL_LISTENER_MAX) {
+ NL_SET_ERR_MSG(info->extack, "too many listeners");
+ return -E2BIG;
+ }
+
err = nla_parse_nested(tb, NFSD_A_SOCK_MAX, attr,
nfsd_sock_nl_policy, info->extack);
if (err < 0)
--
2.55.0
