nfsd_nl_listener_set_doit() matches each requested listener against the existing set in a nested loop that is O(N * M) in the requested (N) and existing (M) counts, run 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 requests carrying more than NFSD_NL_LISTENER_MAX (1024) entries in nfsd_nl_validate_listeners(), before any lock is taken. The limit is far above any realistic configuration. M is not capped here: write_ports() can add listeners too, via svc_addsock() and svc_xprt_create(). But each one costs a real socket, so M is bounded by resources, where N was bounded only by the message size. Capping N leaves ~1M iterations plus 1024 nla_parse_nested() calls under sv_lock as the worst case. Signed-off-by: Jeff Layton <[email protected]> Assisted-by: LLM --- 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 e5844d8454b8..66931caaaaed 100644 --- a/fs/nfsd/nfsctl.c +++ b/fs/nfsd/nfsctl.c @@ -1992,21 +1992,22 @@ static bool nfsd_nl_transport_supported(const char *name) return false; } +/* 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 supported 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, @@ -2015,6 +2016,11 @@ 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
