linux-kernel - Re: [PATCH AUTOSEL 3.18 1/9] bfs: add sanity check at bfs_fill

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Date:   Tue, 13 Nov 2018 08:31:58 +0000
From:   Tigran Aivazian <aivazian.tigran@...il.com>
To:     sashal@...nel.org
Cc:     stable@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        willy@...radead.org, Andrew Morton <akpm@...ux-foundation.org>,
        torvalds@...ux-foundation.org
Subject: Re: [PATCH AUTOSEL 3.18 1/9] bfs: add sanity check at bfs_fill_super()

On Tue, 13 Nov 2018 at 05:52, Sasha Levin <sashal@...nel.org> wrote:
> syzbot is reporting too large memory allocation at bfs_fill_super() [1].
> Since file system image is corrupted such that bfs_sb->s_start == 0,
> bfs_fill_super() is trying to allocate 8MB of continuous memory. Fix
> this by adding a sanity check on bfs_sb->s_start, __GFP_NOWARN and
> printf().
>
> [1] https://syzkaller.appspot.com/bug?id=16a87c236b951351374a84c8a32f40edbc034e96

Hi Sasha,

Thank you, but no, I am rejecting this patch as I have already
submitted a much more robust and accurate (stronger check) patch to
Andrew Morton a couple of days ago against 4.20-rc1.
Andrew, if you would like me to make the same patch against 4.19.1 as
well, please let me know.

Kind regards,
Tigran

>
> Link: http://lkml.kernel.org/r/1525862104-3407-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Reported-by: syzbot <syzbot+71c6b5d68e91149fc8a4@...kaller.appspotmail.com>
> Reviewed-by: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Tigran Aivazian <aivazian.tigran@...il.com>
> Cc: Matthew Wilcox <willy@...radead.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  fs/bfs/inode.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/fs/bfs/inode.c b/fs/bfs/inode.c
> index 90bc079d9982..0ee38b284ad7 100644
> --- a/fs/bfs/inode.c
> +++ b/fs/bfs/inode.c
> @@ -349,7 +349,8 @@ static int bfs_fill_super(struct super_block *s, void *data, int silent)
>
>         s->s_magic = BFS_MAGIC;
>
> -       if (le32_to_cpu(bfs_sb->s_start) > le32_to_cpu(bfs_sb->s_end)) {
> +       if (le32_to_cpu(bfs_sb->s_start) > le32_to_cpu(bfs_sb->s_end) ||
> +           le32_to_cpu(bfs_sb->s_start) < BFS_BSIZE) {
>                 printf("Superblock is corrupted\n");
>                 goto out1;
>         }
> @@ -358,9 +359,11 @@ static int bfs_fill_super(struct super_block *s, void *data, int silent)
>                                         sizeof(struct bfs_inode)
>                                         + BFS_ROOT_INO - 1;
>         imap_len = (info->si_lasti / 8) + 1;
> -       info->si_imap = kzalloc(imap_len, GFP_KERNEL);
> -       if (!info->si_imap)
> +       info->si_imap = kzalloc(imap_len, GFP_KERNEL | __GFP_NOWARN);
> +       if (!info->si_imap) {
> +               printf("Cannot allocate %u bytes\n", imap_len);
>                 goto out1;
> +       }
>         for (i = 0; i < BFS_ROOT_INO; i++)
>                 set_bit(i, info->si_imap);
>
> --
> 2.17.1
>