[PATCH v2 2/2] sunrpc: honor the netlink unix_gid NEGATIVE flag

[Ameer Hamza]

The unix_gid netlink upcall protocol has an explicit
SUNRPC_A_UNIX_GID_NEGATIVE attribute for failed group lookups, and
mountd sends it, but sunrpc_nl_parse_one_unix_gid() only allocates
an empty group list for a flagged reply without propagating the
flag into the entry, so it installs a valid positive entry with
zero groups. Such an entry strips the uid of all supplementary
groups until it is refreshed or expires: the same defect the
previous patch fixes on the classic channel, on a transport that
can say "lookup failed" explicitly.

Set CACHE_NEGATIVE for flagged replies, as the netlink ip_map
path already does for its negative flag. An empty GIDS list
without the flag remains a positive entry.

Fixes: 0850e8603cd7 ("sunrpc: add netlink upcall for the auth.unix.gid cache")
Assisted-by: Claude:claude-fable-5
Signed-off-by: Ameer Hamza <ameer.hamza@xxxxxxxxxxx>
---
 net/sunrpc/svcauth_unix.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/sunrpc/svcauth_unix.c b/net/sunrpc/svcauth_unix.c
index 2f592ba54a366..4dd28749bd5de 100644
--- a/net/sunrpc/svcauth_unix.c
+++ b/net/sunrpc/svcauth_unix.c
@@ -737,6 +737,8 @@ static int sunrpc_nl_parse_one_unix_gid(struct cache_detail *cd,
 			   boot.tv_sec;
 
 	if (tb[SUNRPC_A_UNIX_GID_NEGATIVE]) {
+		/* failed lookup: keep the credential's own groups */
+		set_bit(CACHE_NEGATIVE, &ug.h.flags);
 		ug.gi = groups_alloc(0);
 		if (!ug.gi)
 			return -ENOMEM;
-- 
2.53.0