On Sun, 27 Mar 2022 15:20:42 +0000, Trond Myklebust wrote:
On Sun, 2022-03-27 at 16:02 +0800, Xiaomeng Tong wrote:
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;Hmm... We're not holding any locks on the super block for 'iter' here, so nothing is preventing it from going away while we're.
ok, i am not a 'rcu lock' expert, i will make it hold the rcu_read_lock() if necessary.
Given that we really only want a pointer to the struct pnfs_layoutdriver_type anyway, why not just convert the code to save a pointer to that (and do it while holding the rcu_read_lock())?
Maybe it's not that simple. If you only save a pointer to that and still use 'server' as the list iterator of list_for_each_entry_rcu, there could be problem.
I.e., if no element found in list_for_each_entry_rcu in the first outer 'for' loop, and now 'server' is a bogus pointer to an invalid struct, and continue to go into the second outer 'for' loop, and the check below will lead to invalid memory access (server->pnfs_curr_ld->id), even can potentialy be bypassed with crafted data to make the condition false and mistakely run nfs4_delete_deviceid(server->pnfs_curr_ld, clp, &dev->cbd_dev_id); with bogus 'server'.
if (!server || server->pnfs_curr_ld->id != dev->cbd_layout_type) {
The struct pnfs_layoutdriver is always expected to be a statically allocated structure, so it won't go away as long as the pNFS driver module remains loaded.
-- Xiaomeng Tong