fs/ceph/addr: fix crash after fscrypt_encrypt_pagecache_blocks() error

The function move_dirty_folio_in_page_array() was created by commit ce80b76dd327 ("ceph: introduce ceph_process_folio_batch() method") by moving code from ceph_writepages_start() to this function.

This new function is supposed to return an error code which is checked by the caller (now ceph_process_folio_batch()), and on error, the caller invokes redirty_page_for_writepage() and then breaks from the loop.

However, the refactoring commit has gone wrong, and it by accident, it always returns 0 (= success) because it first NULLs the pointer and then returns PTR_ERR(NULL) which is always 0. This means errors are silently ignored, leaving NULL entries in the page array, which may later crash the kernel.

The simple solution is to call PTR_ERR() before clearing the pointer.

Fixes ce80b76dd327 ("ceph: introduce ceph_process_folio_batch() method")

Link https://lore.kernel.org/ceph-devel/[email protected]/ open here

Cc [email protected]

Signed-off-by Max Kellermann <[email protected]>

---
 fs/ceph/addr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

fs/ceph/addr.c +4 -3

index 8b202d789e93..e3e0d477f3f7 100644
@@ -1264,7 +1264,9 @@ static inline int move_dirty_folio_in_page_array(struct address_space *mapping,
                                                                0,
                                                                gfp_flags);
                if (IS_ERR(pages[index])) {
-                       if (PTR_ERR(pages[index]) == -EINVAL) {
+                       int err = PTR_ERR(pages[index]);
+
+                       if (err == -EINVAL) {
                                pr_err_client(cl, "inode->i_blkbits=%hhu\n",
                                                inode->i_blkbits);
                        }

@@ -1273,7 +1275,7 @@ static inline int move_dirty_folio_in_page_array(struct address_space *mapping,
                        BUG_ON(ceph_wbc->locked_pages == 0);
 
                        pages[index] = NULL;
-                       return PTR_ERR(pages[index]);
+                       return err;
                }
        } else {
                pages[index] = &folio->page;
--

2.47.2