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@xxxxxxxxxxxxxxx
Fixes: 1be5683b03a76 ("pnfs: CB_NOTIFY_DEVICEID")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx>
---
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();
--
2.17.1
