[PATCH 4.14 185/229] NFSv4: Fix races in the legacy idmapper upcall

Greg Kroah-Hartman
2022-08-23T10:13:33Z

From: Trond Myklebust <trond.myklebust@hammerspace.com>

commit 51fd2eb52c0ca8275a906eed81878ef50ae94eb0 upstream.

nfs_idmap_instantiate() will cause the process that is waiting in
request_key_with_auxdata() to wake up and exit. If there is a second
process waiting for the idmap->idmap_mutex, then it may wake up and
start a new call to request_key_with_auxdata(). If the call to
idmap_pipe_downcall() from the first process has not yet finished
calling nfs_idmap_complete_pipe_upcall_locked(), then we may end up
triggering the WARN_ON_ONCE() in nfs_idmap_prepare_pipe_upcall().

The fix is to ensure that we clear idmap->idmap_upcall_data before
calling nfs_idmap_instantiate().

Fixes: e9ab41b620e4 ("NFSv4: Clean up the legacy idmapper upcall")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/nfs/nfs4idmap.c | 46 ++++++++++++++++++++++++----------------------
1 file changed, 24 insertions(+), 22 deletions(-)

--- a/fs/nfs/nfs4idmap.c
+++ b/fs/nfs/nfs4idmap.c
@@ -543,22 +543,20 @@ nfs_idmap_prepare_pipe_upcall(struct idm
return true;
}

-static void
-nfs_idmap_complete_pipe_upcall_locked(struct idmap *idmap, int ret)
+static void nfs_idmap_complete_pipe_upcall(struct idmap_legacy_upcalldata *data,
+ int ret)
{
- struct key *authkey = idmap->idmap_upcall_data->authkey;
-
- kfree(idmap->idmap_upcall_data);
- idmap->idmap_upcall_data = NULL;
- complete_request_key(authkey, ret);
- key_put(authkey);
+ complete_request_key(data->authkey, ret);
+ key_put(data->authkey);
+ kfree(data);
}

-static void
-nfs_idmap_abort_pipe_upcall(struct idmap *idmap, int ret)
+static void nfs_idmap_abort_pipe_upcall(struct idmap *idmap,
+ struct idmap_legacy_upcalldata *data,
+ int ret)
{
- if (idmap->idmap_upcall_data != NULL)
- nfs_idmap_complete_pipe_upcall_locked(idmap, ret);
+ if (cmpxchg(&idmap->idmap_upcall_data, data, NULL) == data)
+ nfs_idmap_complete_pipe_upcall(data, ret);
}

static int nfs_idmap_legacy_upcall(struct key *authkey, void *aux)
@@ -595,7 +593,7 @@ static int nfs_idmap_legacy_upcall(struc

ret = rpc_queue_upcall(idmap->idmap_pipe, msg);
if (ret < 0)
- nfs_idmap_abort_pipe_upcall(idmap, ret);
+ nfs_idmap_abort_pipe_upcall(idmap, data, ret);

return ret;
out2:
@@ -651,6 +649,7 @@ idmap_pipe_downcall(struct file *filp, c
struct request_key_auth *rka;
struct rpc_inode *rpci = RPC_I(file_inode(filp));
struct idmap *idmap = (struct idmap *)rpci->private;
+ struct idmap_legacy_upcalldata *data;
struct key *authkey;
struct idmap_msg im;
size_t namelen_in;
@@ -660,10 +659,11 @@ idmap_pipe_downcall(struct file *filp, c
* will have been woken up and someone else may now have used
* idmap_key_cons - so after this point we may no longer touch it.
*/
- if (idmap->idmap_upcall_data == NULL)
+ data = xchg(&idmap->idmap_upcall_data, NULL);
+ if (data == NULL)
goto out_noupcall;

- authkey = idmap->idmap_upcall_data->authkey;
+ authkey = data->authkey;
rka = get_request_key_auth(authkey);

if (mlen != sizeof(im)) {
@@ -685,18 +685,17 @@ idmap_pipe_downcall(struct file *filp, c
if (namelen_in == 0 || namelen_in == IDMAP_NAMESZ) {
ret = -EINVAL;
goto out;
-}
+ }

- ret = nfs_idmap_read_and_verify_message(&im,
- &idmap->idmap_upcall_data->idmap_msg,
- rka->target_key, authkey);
+ ret = nfs_idmap_read_and_verify_message(&im, &data->idmap_msg,
+ rka->target_key, authkey);
if (ret >= 0) {
key_set_timeout(rka->target_key, nfs_idmap_cache_timeout);
ret = mlen;
}

out:
- nfs_idmap_complete_pipe_upcall_locked(idmap, ret);
+ nfs_idmap_complete_pipe_upcall(data, ret);
out_noupcall:
return ret;
}
@@ -710,7 +709,7 @@ idmap_pipe_destroy_msg(struct rpc_pipe_m
struct idmap *idmap = data->idmap;

if (msg->errno)
- nfs_idmap_abort_pipe_upcall(idmap, msg->errno);
+ nfs_idmap_abort_pipe_upcall(idmap, data, msg->errno);
}

static void
@@ -718,8 +717,11 @@ idmap_release_pipe(struct inode *inode)
{
struct rpc_inode *rpci = RPC_I(inode);
struct idmap *idmap = (struct idmap *)rpci->private;
+ struct idmap_legacy_upcalldata *data;

- nfs_idmap_abort_pipe_upcall(idmap, -EPIPE);
+ data = xchg(&idmap->idmap_upcall_data, NULL);
+ if (data)
+ nfs_idmap_complete_pipe_upcall(data, -EPIPE);
}

int nfs_map_name_to_uid(const struct nfs_server *server, const char *name, size_t namelen, kuid_t *uid)