Re: [PATCH] nilfs2: add ratelimiting to nilfs2 message

[Ryusuke Konishi <konishi.ryusuke@gmail.com>]

On Sat, Sep 28, 2024 at 12:19 AM Lizhi Xu wrote:
>
> Syzbot report a task hung in vcs_open.
> When rec_len too small in nilfs_check_folio, it can result in a huge flood
> of messages being sent to the console. It eventually caused tty to hung when
> retrieving the console_lock().
>
> Reported-by: syzbot+8a192e8d090fa9a31135@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=8a192e8d090fa9a31135
> Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
> ---
>  fs/nilfs2/dir.c | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)

Thank you for the patch.

I could confirm that the problem is reproducible and that your patch
prevents it, so I will treat this as a nilfs2 side issue.

The patch seems somewhat straightforward, so let me review this a bit
more.  I may ask you to make some changes.

Thanks,
Ryusuke Konishi

>
> diff --git a/fs/nilfs2/dir.c b/fs/nilfs2/dir.c
> index fe5b1a30c509..0a89dda75414 100644
> --- a/fs/nilfs2/dir.c
> +++ b/fs/nilfs2/dir.c
> @@ -32,6 +32,7 @@
>  #include <linux/pagemap.h>
>  #include "nilfs.h"
>  #include "page.h"
> +#include <linux/ratelimit.h>
>
>  static inline unsigned int nilfs_rec_len_from_disk(__le16 dlen)
>  {
> @@ -115,6 +116,7 @@ static bool nilfs_check_folio(struct folio *folio, char *kaddr)
>         size_t limit = folio_size(folio);
>         struct nilfs_dir_entry *p;
>         char *error;
> +       static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL * 5, 1);
>
>         if (dir->i_size < folio_pos(folio) + limit) {
>                 limit = dir->i_size - folio_pos(folio);
> @@ -148,9 +150,11 @@ static bool nilfs_check_folio(struct folio *folio, char *kaddr)
>         /* Too bad, we had an error */
>
>  Ebadsize:
> -       nilfs_error(sb,
> -                   "size of directory #%lu is not a multiple of chunk size",
> -                   dir->i_ino);
> +       if (__ratelimit(&rs)) {
> +               nilfs_error(sb,
> +                           "size of directory #%lu is not a multiple of chunk size",
> +                           dir->i_ino);
> +       }
>         goto fail;
>  Eshort:
>         error = "rec_len is smaller than minimal";
> @@ -167,18 +171,22 @@ static bool nilfs_check_folio(struct folio *folio, char *kaddr)
>  Einumber:
>         error = "disallowed inode number";
>  bad_entry:
> -       nilfs_error(sb,
> +       if (__ratelimit(&rs)) {
> +               nilfs_error(sb,
>                     "bad entry in directory #%lu: %s - offset=%lu, inode=%lu, rec_len=%zd, name_len=%d",
>                     dir->i_ino, error, (folio->index << PAGE_SHIFT) + offs,
>                     (unsigned long)le64_to_cpu(p->inode),
>                     rec_len, p->name_len);
> +       }
>         goto fail;
>  Eend:
>         p = (struct nilfs_dir_entry *)(kaddr + offs);
> -       nilfs_error(sb,
> -                   "entry in directory #%lu spans the page boundary offset=%lu, inode=%lu",
> -                   dir->i_ino, (folio->index << PAGE_SHIFT) + offs,
> -                   (unsigned long)le64_to_cpu(p->inode));
> +       if (__ratelimit(&rs)) {
> +               nilfs_error(sb,
> +                           "entry in directory #%lu spans the page boundary offset=%lu, inode=%lu",
> +                           dir->i_ino, (folio->index << PAGE_SHIFT) + offs,
> +                           (unsigned long)le64_to_cpu(p->inode));
> +       }
>  fail:
>         return false;
>  }
> --
> 2.43.0
>