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

[Mike Rapoport <rppt@linux.ibm.com>]

On Wed, Aug 19, 2020 at 07:57:10PM +0100, 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>

Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>

> ---
>  mm/debug.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> 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:
> -- 
> 2.28.0
> 

-- 
Sincerely yours,
Mike.