Re: [PATCH] fs/ceph/addr: fix crash after fscrypt_encrypt_pagecache_blocks() error

[Ilya Dryomov]

On Thu, Aug 28, 2025 at 1:16 PM Max Kellermann <max.kellermann@xxxxxxxxx> wrote:
>
> 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/aK4v548CId5GIKG1@xxxxxxxxxxxxxx/
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
> ---
>  fs/ceph/addr.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> index 8b202d789e93..e3e0d477f3f7 100644
> --- a/fs/ceph/addr.c
> +++ b/fs/ceph/addr.c
> @@ -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
>

Queued up for 6.17-rc6.

Thanks,

                Ilya