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sunrpc: treat empty auth.unix.gid replies as negative entries

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When rpc.mountd cannot resolve a uid (getpwuid() or getgrouplist()
failure, e.g. while winbind or sssd is briefly unreachable), it
answers the auth.unix.gid upcall with zero groups. unix_gid_parse()
installs that as a valid positive entry, and svcauth_unix_set_client()
then replaces the credential's group list with the empty one on
every request, RPCSEC_GSS included via svcauth_gss_set_client().
One failed lookup strips that uid of all supplementary groups on
every export for up to mountd's configured TTL (30 minutes by
default), long after the NSS backend has recovered.

mountd cannot send an empty list for a successful lookup, since
getgrouplist(3) always includes at least the user's primary group,
so a zero-group reply can only mean the lookup failed. Record it as
a negative entry: unix_gid_find() then returns -ENOENT and
svcauth_unix_set_client() keeps the groups the RPC credential
already carries. This is the fallback that
commit 3fc605a2aa ("[PATCH] knfsd: allow the server to provide a
gid list when using AUTH_UNIX authentication") promised when no
answer is available, and the same state try_to_negate_entry()
already creates when no listener holds the channel open.

Fixes: 3fc605a2aa ("[PATCH] knfsd: allow the server to provide a gid list when using AUTH_UNIX authentication")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-fable-5
Signed-off-by: Ameer Hamza <ameer.hamza@truenas.com>
Link: https://patch.msgid.link/20260814221953.108837-2-ameer.hamza@truenas.com
Signed-off-by: Chuck Lever <cel@kernel.org>
This commit is contained in:
Ameer Hamza 2026-08-15 03:19:52 +05:00 committed by Chuck Lever
parent 47f9c6a305
commit a12cc09302
1 changed files with 7 additions and 0 deletions
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7
net/sunrpc/svcauth_unix.c
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@ -540,6 +540,13 @@ static int unix_gid_parse(struct cache_detail *cd,
if (ugp) {
struct cache_head *ch;
ug.h.flags = 0;
/*
* mountd sends at least the user's primary group on
* success, so an empty list can only mean the lookup
* failed. Keep the credential's own groups instead.
*/
if (gids == 0)
set_bit(CACHE_NEGATIVE, &ug.h.flags);
ug.h.expiry_time = expiry;
ch = sunrpc_cache_update(cd,
&ug.h, &ugp->h,