Re: [PATCH] mm/debug: Do not dereference i_ino blindly

[John Hubbard <jhubbard@nvidia.com>]

On 8/19/20 11:57 AM, Matthew Wilcox (Oracle) wrote:
> We check i_dentry is fetchable and i_ino is earlier in the struct
> than i_ino, so it ought to work fine, but it's possible that struct
> randomisation has reordered i_ino after i_dentry and the pointer is
> just wild enough that i_dentry is fetchable and i_ino isn't.
> 
> Also print the inode number if the dentry is invalid.
> 
> Reported-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>   mm/debug.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
> 

It's hard to write software that reports what's wrong with
itself. Let's just keep adding to the pile, then. :)

Reviewed-by: John Hubbard <jhubbard@nvidia.com>


thanks,
-- 
John Hubbard
NVIDIA

> diff --git a/mm/debug.c b/mm/debug.c
> index ca8d1cacdecc..2a767865145c 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -120,6 +120,7 @@ void __dump_page(struct page *page, const char *reason)
>   		struct hlist_node *dentry_first;
>   		struct dentry *dentry_ptr;
>   		struct dentry dentry;
> +		unsigned long ino;
>   
>   		/*
>   		 * mapping can be invalid pointer and we don't want to crash
> @@ -136,21 +137,22 @@ void __dump_page(struct page *page, const char *reason)
>   			goto out_mapping;
>   		}
>   
> -		if (get_kernel_nofault(dentry_first, &host->i_dentry.first)) {
> +		if (get_kernel_nofault(dentry_first, &host->i_dentry.first) ||
> +		    get_kernel_nofault(ino, &host->i_ino)) {
>   			pr_warn("aops:%ps with invalid host inode %px\n",
>   					a_ops, host);
>   			goto out_mapping;
>   		}
>   
>   		if (!dentry_first) {
> -			pr_warn("aops:%ps ino:%lx\n", a_ops, host->i_ino);
> +			pr_warn("aops:%ps ino:%lx\n", a_ops, ino);
>   			goto out_mapping;
>   		}
>   
>   		dentry_ptr = container_of(dentry_first, struct dentry, d_u.d_alias);
>   		if (get_kernel_nofault(dentry, dentry_ptr)) {
> -			pr_warn("aops:%ps with invalid dentry %px\n", a_ops,
> -					dentry_ptr);
> +			pr_warn("aops:%ps ino:%lx with invalid dentry %px\n",
> +					a_ops, ino, dentry_ptr);
>   		} else {
>   			/*
>   			 * if dentry is corrupted, the %pd handler may still
> @@ -158,7 +160,7 @@ void __dump_page(struct page *page, const char *reason)
>   			 * corrupted struct page
>   			 */
>   			pr_warn("aops:%ps ino:%lx dentry name:\"%pd\"\n",
> -					a_ops, host->i_ino, &dentry);
> +					a_ops, ino, &dentry);
>   		}
>   	}
>   out_mapping:
>