[PATCH 0/5] Fix premature completion of rpc_pipefs upcalls

[PATCH 0/5] Fix premature completion of rpc_pipefs upcalls

[Chuck Lever]

Farhad Alemi's syzkaller run against 7.1-rc5 hit a KASAN
vmalloc-out-of-bounds in rpc_queue_upcall() while NFSD was starting
client tracking:

  https://lore.kernel.org/linux-nfs/CA+0ovCjVF58WLeen2ctdzHyWUASAAW3Y=Yjihyq0pFApYawtDg@mail.gmail.com/

The cld downcall matches a reply to its upcall by xid alone. If a
write arrives before nfsdcld has read the upcall, the waiter returns
while its struct rpc_pipe_msg is still queued, and the pipe is left
holding a list_head into a dead stack frame. The blocklayout device
upcall has the same bug, plus two of its own: the waiter can go to
sleep after the reply has arrived, and a reply left over from a
purged upcall is taken as a fresh one.

rpc_pipefs pipes are mode 0600, so the writer is a daemon running as
root. These patches guard against a broken or hostile daemon, which
is unlikely. So consider the series as hardening rather than urgent.

The gss and idmap consumers keep their message in an object that
lives as long as the upcall and do not have this problem. The cld
and blocklayout fixes also complete only once the daemon has
consumed the whole message, and keep the message somewhere that
outlives the waiter.

Reading cld_pipe_downcall() for the fix turned up two unrelated
problems. A faulting reply copy strands the waiter and hangs NFSD
shutdown behind it, and an unchecked principal hash length reads past
a stack array in nfsd4_cld_check_v2().

Farhad, a run of your reproducer against this series would help.

---
Chuck Lever (5):
      NFSD: Don't complete a cld upcall the daemon has not read
      NFSD: Move the cld upcall message out of the caller's stack frame
      NFSD: Complete a cld upcall when copying its reply fails
      NFSD: Reject an oversized principal hash from nfsdcld
      pnfs/blocklayout: Complete a device upcall only on its own reply

 fs/nfs/blocklayout/blocklayout.h |  5 ----
 fs/nfs/blocklayout/rpc_pipefs.c  | 56 +++++++++++++++++++++++++---------------
 fs/nfs/netns.h                   |  5 +++-
 fs/nfsd/nfs4recover.c            | 53 +++++++++++++++++++++++++++----------
 4 files changed, 78 insertions(+), 41 deletions(-)
---
base-commit: e3c3b1a8188b192b125ae1fc9861d9a5d8d43d85
change-id: 20260830-alemi-d9f420956e8d

Best regards,
--  
Chuck Lever

[PATCH 1/5] NFSD: Don't complete a cld upcall the daemon has not read

[Chuck Lever]

cld_pipe_downcall() matches a reply to its upcall on the xid alone.
A write that arrives before the daemon has read that upcall
completes __cld_pipe_upcall() while its struct rpc_pipe_msg is still
queued on the pipe. The waiter returns, its stack frame goes away,
and the pipe keeps a list_head that points into it. The next
rpc_queue_upcall() walks that pointer:

  BUG: KASAN: vmalloc-out-of-bounds in __list_add_valid_or_report
  Read of size 8 at addr ffffc90007027950 by task syz.0.96/13066
   __list_add_valid_or_report+0x6a/0x130
   rpc_queue_upcall
   cld_pipe_upcall
   nfsd4_cld_grace_start
   nfsd4_cld_tracking_init

The pipe is mode 0600 in rpc_pipefs, so the trigger is a broken or
hostile nfsdcld rather than an unprivileged task.

Record whether the daemon has consumed the whole message and
complete only when it has. cld_pipe_destroy_msg() runs on every path
by which the pipe releases a message, so it can maintain that flag
under cn_lock. nfsdcld sends its -EINPROGRESS downcalls only after
reading the upcall, so the new check does not break the GraceStart
record stream.

Fixes: f3f8014862d8 ("nfsd: add the infrastructure to handle the cld upcall")
Reported-by: Farhad Alemi <farhad.alemi@berkeley.edu>
Closes: https://lore.kernel.org/linux-nfs/CA+0ovCjVF58WLeen2ctdzHyWUASAAW3Y=Yjihyq0pFApYawtDg@mail.gmail.com/
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfsd/nfs4recover.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index aee3a0b22d1c..22a9a366d7eb 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -648,6 +648,8 @@ struct cld_upcall {
 	struct list_head	 cu_list;
 	struct cld_net		*cu_net;
 	struct completion	 cu_done;
+	/* daemon has read the whole upcall; protected by cn_lock */
+	bool			 cu_inflight;
 	union {
 		struct cld_msg_hdr	 cu_hdr;
 		struct cld_msg		 cu_msg;
@@ -808,6 +810,13 @@ cld_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
 	spin_lock(&cn->cn_lock);
 	list_for_each_entry(tmp, &cn->cn_list, cu_list) {
 		if (get_unaligned(&tmp->cu_u.cu_hdr.cm_xid) == xid) {
+			/*
+			 * Completing now would return the waiter
+			 * while its message is still queued on the
+			 * pipe.
+			 */
+			if (!tmp->cu_inflight)
+				break;
 			cup = tmp;
 			if (status != -EINPROGRESS)
 				list_del_init(&cup->cu_list);
@@ -816,9 +825,9 @@ cld_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
 	}
 	spin_unlock(&cn->cn_lock);
 
-	/* couldn't find upcall? */
+	/* no upcall to complete? */
 	if (!cup) {
-		dprintk("%s: couldn't find upcall -- xid=%u\n", __func__, xid);
+		dprintk("%s: no completable upcall -- xid=%u\n", __func__, xid);
 		return -EINVAL;
 	}
 
@@ -838,8 +847,16 @@ cld_pipe_destroy_msg(struct rpc_pipe_msg *msg)
 	struct cld_msg *cmsg = msg->data;
 	struct cld_upcall *cup = container_of(cmsg, struct cld_upcall,
 						 cu_u.cu_msg);
+	struct cld_net *cn = cup->cu_net;
+
+	/*
+	 * errno >= 0 means the daemon read the whole message and a
+	 * downcall will complete the upcall.
+	 */
+	spin_lock(&cn->cn_lock);
+	cup->cu_inflight = msg->errno >= 0;
+	spin_unlock(&cn->cn_lock);
 
-	/* errno >= 0 means we got a downcall */
 	if (msg->errno >= 0)
 		return;
 

-- 
2.54.0

[PATCH 2/5] NFSD: Move the cld upcall message out of the caller's stack frame

[Chuck Lever]

__cld_pipe_upcall() builds its struct rpc_pipe_msg on the stack and
hands it to rpc_queue_upcall(), which links it into a list the pipe
owns until the message is released. Only the completion rules keep that
frame alive for as long as the pipe refers to it, and the peer that
drives those rules is an untrusted userspace daemon. The gss and idmap
upcalls do not take that on: each keeps the message in the object it
already allocates.

Do the same here and put the message in struct cld_upcall, beside the
reply buffer it carries. cld_pipe_destroy_msg() then reaches the upcall
from the message directly rather than through msg->data.

Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfsd/nfs4recover.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index 22a9a366d7eb..8dff351aa832 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -650,6 +650,7 @@ struct cld_upcall {
 	struct completion	 cu_done;
 	/* daemon has read the whole upcall; protected by cn_lock */
 	bool			 cu_inflight;
+	struct rpc_pipe_msg	 cu_pipe_msg;
 	union {
 		struct cld_msg_hdr	 cu_hdr;
 		struct cld_msg		 cu_msg;
@@ -661,22 +662,22 @@ static int
 __cld_pipe_upcall(struct rpc_pipe *pipe, void *cmsg, struct nfsd_net *nn)
 {
 	int ret;
-	struct rpc_pipe_msg msg;
 	struct cld_upcall *cup = container_of(cmsg, struct cld_upcall, cu_u);
+	struct rpc_pipe_msg *msg = &cup->cu_pipe_msg;
 
-	memset(&msg, 0, sizeof(msg));
-	msg.data = cmsg;
-	msg.len = nn->client_tracking_ops->msglen;
+	memset(msg, 0, sizeof(*msg));
+	msg->data = cmsg;
+	msg->len = nn->client_tracking_ops->msglen;
 
-	ret = rpc_queue_upcall(pipe, &msg);
+	ret = rpc_queue_upcall(pipe, msg);
 	if (ret < 0) {
 		goto out;
 	}
 
 	wait_for_completion(&cup->cu_done);
 
-	if (msg.errno < 0)
-		ret = msg.errno;
+	if (msg->errno < 0)
+		ret = msg->errno;
 out:
 	return ret;
 }
@@ -844,9 +845,8 @@ cld_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
 static void
 cld_pipe_destroy_msg(struct rpc_pipe_msg *msg)
 {
-	struct cld_msg *cmsg = msg->data;
-	struct cld_upcall *cup = container_of(cmsg, struct cld_upcall,
-						 cu_u.cu_msg);
+	struct cld_upcall *cup = container_of(msg, struct cld_upcall,
+						 cu_pipe_msg);
 	struct cld_net *cn = cup->cu_net;
 
 	/*

-- 
2.54.0

[PATCH 3/5] NFSD: Complete a cld upcall when copying its reply fails

[Chuck Lever]

cld_pipe_downcall() removes the matching upcall from cn_list before
copying the daemon's reply. When that copy_from_user() faults, the
downcall returns -EFAULT without completing the upcall, and a
retried write cannot reach it because its xid is no longer on the
list. __cld_pipe_upcall() waits on cu_done uninterruptibly, so the
nfsd thread that sent the upcall is stuck, and nfsd shutdown hangs
behind it. The pipe is mode 0600, so only a broken or hostile
nfsdcld can trigger the fault.

Record the fault in the upcall's pipe message and complete it, so
the waiter returns the error to its client tracking operation.

Fixes: f3f8014862d8 ("nfsd: add the infrastructure to handle the cld upcall")
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfsd/nfs4recover.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index 8dff351aa832..999694db9981 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -835,8 +835,11 @@ cld_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
 	if (status == -EINPROGRESS)
 		return __cld_pipe_inprogress_downcall(cmsg, nn);
 
-	if (copy_from_user(&cup->cu_u.cu_msg_v2, src, mlen) != 0)
+	if (copy_from_user(&cup->cu_u.cu_msg_v2, src, mlen) != 0) {
+		cup->cu_pipe_msg.errno = -EFAULT;
+		complete(&cup->cu_done);
 		return -EFAULT;
+	}
 
 	complete(&cup->cu_done);
 	return mlen;

-- 
2.54.0

[PATCH 4/5] NFSD: Reject an oversized principal hash from nfsdcld

[Chuck Lever]

__cld_pipe_inprogress_downcall() takes the principal hash length
from the daemon's GraceStart downcall without checking it against
the cc_princhash payload it describes, which holds at most
SHA256_DIGEST_SIZE bytes. The length is stored verbatim in the
reclaim record, and nfsd4_cld_check_v2() later hands it to memcmp()
against a digest array of SHA256_DIGEST_SIZE bytes on the stack. A
length up to U8_MAX reads past the end of that array, and the stray
bytes can only make the comparison fail, denying the client its
reclaim. The pipe is mode 0600 in rpc_pipefs, so the trigger is a
broken or hostile nfsdcld rather than an unprivileged task.

Reject a length larger than the wire field, as the existing check
on the client name length does.

Fixes: 6ee95d1c8991 ("nfsd: add support for upcall version 2")
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfsd/nfs4recover.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index 999694db9981..8af935ed0c4e 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -730,6 +730,11 @@ __cld_pipe_inprogress_downcall(const struct cld_msg_v2 __user *cmsg,
 			name.len = namelen;
 			if (get_user(princhashlen, &ci->cc_princhash.cp_len))
 				return -EFAULT;
+			if (princhashlen > SHA256_DIGEST_SIZE) {
+				dprintk("%s: invalid princhashlen (%u)",
+					__func__, princhashlen);
+				return -EINVAL;
+			}
 			if (princhashlen > 0) {
 				princhashcopy = memdup_user(
 					&ci->cc_princhash.cp_data,

-- 
2.54.0

[PATCH 5/5] pnfs/blocklayout: Complete a device upcall only on its own reply

[Chuck Lever]

bl_pipe_downcall() wakes bl_resolve_deviceid() on any write of the
right size, without checking that blkmapd has read the upcall being
replied to. A write that arrives first returns the waiter while its
struct rpc_pipe_msg is still queued on the pipe, which then holds a
list_head into a dead stack frame. Reaching the pipe takes root, so
the trigger is a broken or hostile blkmapd.

The wait has two further defects. bl_resolve_deviceid() sets
TASK_UNINTERRUPTIBLE only after rpc_queue_upcall() has made the
message visible, so a reply that lands in between wakes a running
task and the schedule() that follows sleeps forever holding
bl_mutex. And nn->bl_mount_reply is never reset, so when the pipe
purges an unread upcall the waiter takes the previous reply as its
own.

Move the message into struct nfs_net, where bl_mutex already limits
the pipe to one upcall per net namespace. Accept a reply only while
blkmapd has read the whole message and no earlier reply has been
taken, and reject any other write with -EINVAL. Wait for that reply
on a completion so it cannot slip past the sleep, and check
msg->errno before trusting it.

Fixes: fe0a9b740881 ("pnfsblock: add device operations")
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfs/blocklayout/blocklayout.h |  5 ----
 fs/nfs/blocklayout/rpc_pipefs.c  | 56 +++++++++++++++++++++++++---------------
 fs/nfs/netns.h                   |  5 +++-
 3 files changed, 39 insertions(+), 27 deletions(-)

diff --git a/fs/nfs/blocklayout/blocklayout.h b/fs/nfs/blocklayout/blocklayout.h
index 6da40ca19570..e242b1d5b4bd 100644
--- a/fs/nfs/blocklayout/blocklayout.h
+++ b/fs/nfs/blocklayout/blocklayout.h
@@ -161,11 +161,6 @@ BLK_LSEG2EXT(struct pnfs_layout_segment *lseg)
 	return BLK_LO2EXT(lseg->pls_layout);
 }
 
-struct bl_pipe_msg {
-	struct rpc_pipe_msg msg;
-	wait_queue_head_t *bl_wq;
-};
-
 struct bl_msg_hdr {
 	u8  type;
 	u16 totallen; /* length of entire message, including hdr itself */
diff --git a/fs/nfs/blocklayout/rpc_pipefs.c b/fs/nfs/blocklayout/rpc_pipefs.c
index d526f5ba7887..63db51759658 100644
--- a/fs/nfs/blocklayout/rpc_pipefs.c
+++ b/fs/nfs/blocklayout/rpc_pipefs.c
@@ -55,17 +55,15 @@ bl_resolve_deviceid(struct nfs_server *server, struct pnfs_block_volume *b,
 	struct net *net = server->nfs_client->cl_net;
 	struct nfs_net *nn = net_generic(net, nfs_net_id);
 	struct bl_dev_msg *reply = &nn->bl_mount_reply;
-	struct bl_pipe_msg bl_pipe_msg;
-	struct rpc_pipe_msg *msg = &bl_pipe_msg.msg;
+	struct rpc_pipe_msg *msg = &nn->bl_pipe_msg;
+	struct rpc_pipe *pipe = nn->bl_device_pipe;
 	struct bl_msg_hdr *bl_msg;
-	DECLARE_WAITQUEUE(wq, current);
 	dev_t dev = 0;
 	int rc;
 
 	dprintk("%s CREATING PIPEFS MESSAGE\n", __func__);
 
 	mutex_lock(&nn->bl_mutex);
-	bl_pipe_msg.bl_wq = &nn->bl_wq;
 
 	b->simple.len += 4;	/* single volume */
 	if (b->simple.len > PAGE_SIZE)
@@ -83,17 +81,20 @@ bl_resolve_deviceid(struct nfs_server *server, struct pnfs_block_volume *b,
 	nfs4_encode_simple(msg->data + sizeof(*bl_msg), b);
 
 	dprintk("%s CALLING USERSPACE DAEMON\n", __func__);
-	add_wait_queue(&nn->bl_wq, &wq);
-	rc = rpc_queue_upcall(nn->bl_device_pipe, msg);
-	if (rc < 0) {
-		remove_wait_queue(&nn->bl_wq, &wq);
+	reinit_completion(&nn->bl_done);
+	rc = rpc_queue_upcall(pipe, msg);
+	if (rc < 0)
 		goto out_free_data;
-	}
 
-	set_current_state(TASK_UNINTERRUPTIBLE);
-	schedule();
-	remove_wait_queue(&nn->bl_wq, &wq);
+	wait_for_completion(&nn->bl_done);
 
+	/* Retire the upcall so bl_pipe_downcall() rejects a later write. */
+	spin_lock(&pipe->lock);
+	msg->copied = 0;
+	spin_unlock(&pipe->lock);
+
+	if (msg->errno < 0)
+		goto out_free_data;
 	if (reply->status != BL_DEVICE_REQUEST_PROC) {
 		printk(KERN_WARNING "%s failed to decode device: %d\n",
 			__func__, reply->status);
@@ -113,26 +114,39 @@ static ssize_t bl_pipe_downcall(struct file *filp, const char __user *src,
 {
 	struct nfs_net *nn = net_generic(file_inode(filp)->i_sb->s_fs_info,
 					 nfs_net_id);
+	struct rpc_pipe *pipe = nn->bl_device_pipe;
+	struct bl_dev_msg reply;
+	bool accepted;
 
-	if (mlen != sizeof (struct bl_dev_msg))
+	if (mlen != sizeof(reply))
 		return -EINVAL;
-
-	if (copy_from_user(&nn->bl_mount_reply, src, mlen) != 0)
+	if (copy_from_user(&reply, src, mlen) != 0)
 		return -EFAULT;
 
-	wake_up(&nn->bl_wq);
-
+	/*
+	 * Only the first reply counts, and only after blkmapd has read
+	 * the whole upcall and before bl_resolve_deviceid() retires it.
+	 */
+	spin_lock(&pipe->lock);
+	accepted = rpc_msg_is_inflight(&nn->bl_pipe_msg) &&
+		   !completion_done(&nn->bl_done);
+	if (accepted) {
+		nn->bl_mount_reply = reply;
+		complete(&nn->bl_done);
+	}
+	spin_unlock(&pipe->lock);
+	if (!accepted)
+		return -EINVAL;
 	return mlen;
 }
 
 static void bl_pipe_destroy_msg(struct rpc_pipe_msg *msg)
 {
-	struct bl_pipe_msg *bl_pipe_msg =
-		container_of(msg, struct bl_pipe_msg, msg);
+	struct nfs_net *nn = container_of(msg, struct nfs_net, bl_pipe_msg);
 
 	if (msg->errno >= 0)
 		return;
-	wake_up(bl_pipe_msg->bl_wq);
+	complete(&nn->bl_done);
 }
 
 static const struct rpc_pipe_ops bl_upcall_ops = {
@@ -221,7 +235,7 @@ static int nfs4blocklayout_net_init(struct net *net)
 	int err;
 
 	mutex_init(&nn->bl_mutex);
-	init_waitqueue_head(&nn->bl_wq);
+	init_completion(&nn->bl_done);
 	nn->bl_device_pipe = rpc_mkpipe_data(&bl_upcall_ops, 0);
 	if (IS_ERR(nn->bl_device_pipe))
 		return PTR_ERR(nn->bl_device_pipe);
diff --git a/fs/nfs/netns.h b/fs/nfs/netns.h
index 36658579100d..e1decff366d4 100644
--- a/fs/nfs/netns.h
+++ b/fs/nfs/netns.h
@@ -10,6 +10,8 @@
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 #include <linux/sunrpc/stats.h>
+#include <linux/sunrpc/rpc_pipe_fs.h>
+#include <linux/completion.h>
 
 struct bl_dev_msg {
 	int32_t status;
@@ -21,8 +23,9 @@ struct nfs_netns_client;
 struct nfs_net {
 	struct cache_detail *nfs_dns_resolve;
 	struct rpc_pipe *bl_device_pipe;
+	struct rpc_pipe_msg bl_pipe_msg;
 	struct bl_dev_msg bl_mount_reply;
-	wait_queue_head_t bl_wq;
+	struct completion bl_done;
 	struct mutex bl_mutex;
 	struct list_head nfs_client_list;
 	struct list_head nfs_volume_list;

-- 
2.54.0