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([2405:201:682f:383f:a1f4:8b77:c28c:48f5]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3607ee0cab0sm28859299eec.3.2026.10.18.04.33.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 18 Oct 2026 04:33:22 -0700 (PDT) From: Deepanshu Kartikey To: cel@kernel.org, jlayton@kernel.org, neil@brown.name, okorniev@redhat.com, Dai.Ngo@oracle.com, tom@talpey.com Cc: bfields@fieldses.org, skinsbursky@parallels.com, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+561b859d032c8bf2fb53@syzkaller.appspotmail.com Subject: [PATCH] nfsd: fix out-of-bounds read of sv_permsocks when starting a thread Date: Sun, 18 Oct 2026 17:03:12 +0530 Message-ID: <20261018113312.10455-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit nfsd() derives its struct net from the first entry of serv->sv_permsocks using list_entry() without checking that the list is non-empty. If the list is empty, list_entry() returns a bogus svc_xprt computed from the list head embedded in struct svc_serv, and the following perm_sock->xpt_net load reads far past the end of the svc_serv allocation: BUG: KASAN: slab-out-of-bounds in nfsd+0x118/0xbc0 fs/nfsd/nfssvc.c:894 Read of size 8 at addr ffff88802d423f50 by task nfsd/5988 The list can be empty because nothing guarantees that a permanent listener exists while a thread starts. With dynamic thread spawning, a thread can begin running after the last listener has been closed and removed. Take sv_lock, which protects sv_permsocks, and check for an empty list and read xpt_net in the same critical section. If there is no permanent socket, report -ENOTCONN through svc_thread_init_status(), which wakes the creator and exits the thread, instead of dereferencing a bogus pointer. Fixes: 88c476661719 ("nfsd: pass proper net to nfsd_destroy() from NFSd kthreads") Reported-by: syzbot+561b859d032c8bf2fb53@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=561b859d032c8bf2fb53 Tested-by: syzbot+561b859d032c8bf2fb53@syzkaller.appspotmail.com Signed-off-by: Deepanshu Kartikey --- fs/nfsd/nfssvc.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-) diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c index 2edf716ea022..da6fce79efae 100644 --- a/fs/nfsd/nfssvc.c +++ b/fs/nfsd/nfssvc.c @@ -890,17 +890,31 @@ nfsd(void *vrqstp) { struct svc_rqst *rqstp = (struct svc_rqst *) vrqstp; struct svc_pool *pool = rqstp->rq_pool; - struct svc_xprt *perm_sock = list_entry(rqstp->rq_server->sv_permsocks.next, typeof(struct svc_xprt), xpt_list); - struct net *net = perm_sock->xpt_net; - struct nfsd_net *nn = net_generic(net, nfsd_net_id); + struct svc_serv *serv = rqstp->rq_server; + struct svc_xprt *perm_sock; + struct net *net = NULL; + struct nfsd_net *nn = NULL; struct nfsd_thread_local_info ntli = { }; bool have_mutex = false; + int err = 0; + + spin_lock_bh(&serv->sv_lock); + if (list_empty(&serv->sv_permsocks)) { + err = -ENOTCONN; + } else { + perm_sock = list_first_entry(&serv->sv_permsocks, + struct svc_xprt, xpt_list); + net = perm_sock->xpt_net; + } + spin_unlock_bh(&serv->sv_lock); + if (!err) + nn = net_generic(net, nfsd_net_id); /* At this point, the thread shares current->fs * with the init process. We need to create files with the * umask as defined by the client instead of init's umask. */ - svc_thread_init_status(rqstp, unshare_fs_struct()); + svc_thread_init_status(rqstp, err ?: unshare_fs_struct()); current->fs->umask = 0; -- 2.43.0