The bug is here: if (!server || server->pnfs_curr_ld->id != dev->cbd_layout_type) {
The list iterator value 'server' will *always* be set and non-NULL by list_for_each_entry_rcu, so it is incorrect to assume that the iterator value will be NULL if the list is empty or no element is found (In fact, it will be a bogus pointer to an invalid struct object containing the HEAD, which is used for above check at next outer loop). Otherwise it may bypass the check in theory (iif server->pnfs_curr_ld->id == dev->cbd_layout_type, 'server' now is a bogus pointer) and lead to invalid memory access passing the check.
To fix the bug, use a new variable 'iter' as the list iterator, while use the original variable 'server' as a dedicated pointer to point to the found element.
Cc: stable@vger.kernel.org Fixes: 1be5683b03a76 ("pnfs: CB_NOTIFY_DEVICEID") Signed-off-by: Xiaomeng Tong xiam0nd.tong@gmail.com --- fs/nfs/callback_proc.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/fs/nfs/callback_proc.c b/fs/nfs/callback_proc.c index c343666d9a42..84779785dc8d 100644 --- a/fs/nfs/callback_proc.c +++ b/fs/nfs/callback_proc.c @@ -361,7 +361,7 @@ __be32 nfs4_callback_devicenotify(void *argp, void *resp, uint32_t i; __be32 res = 0; struct nfs_client *clp = cps->clp; - struct nfs_server *server = NULL; + struct nfs_server *server = NULL, *iter;
if (!clp) { res = cpu_to_be32(NFS4ERR_OP_NOT_IN_SESSION); @@ -374,10 +374,11 @@ __be32 nfs4_callback_devicenotify(void *argp, void *resp, if (!server || server->pnfs_curr_ld->id != dev->cbd_layout_type) { rcu_read_lock(); - list_for_each_entry_rcu(server, &clp->cl_superblocks, client_link) - if (server->pnfs_curr_ld && - server->pnfs_curr_ld->id == dev->cbd_layout_type) { + list_for_each_entry_rcu(iter, &clp->cl_superblocks, client_link) + if (iter->pnfs_curr_ld && + iter->pnfs_curr_ld->id == dev->cbd_layout_type) { rcu_read_unlock(); + server = iter; goto found; } rcu_read_unlock();