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Date: Wed, 5 Sep 2018 13:57:17 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Dominique Martinet <asmadeus@codewreck.org>
Cc: Omar Sandoval <osandov@osandov.com>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Eric Biederman <ebiederm@xmission.com>,
        James Morse <james.morse@arm.com>,
        Bhupesh Sharma <bhsharma@redhat.com>, kernel-team@fb.com
Subject: Re: [PATCH v3] proc/kcore: fix invalid memory access in multi-page
 read optimization
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On Wed,  5 Sep 2018 00:38:22 +0200 Dominique Martinet <asmadeus@codewreck.org> wrote:

> The 'm' kcore_list item could point to kclist_head, and it is incorrect to
> look at m->addr / m->size in this case.
> There is no choice but to run through the list of entries for every address
> if we did not find any entry in the previous iteration
> 
> Reset 'm' to NULL in that case at Omar Sandoval's suggestion.
> 
> ...
>
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -464,6 +464,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
>  				ret = -EFAULT;
>  				goto out;
>  			}
> +			m = NULL;
>  		} else if (m->type == KCORE_VMALLOC) {
>  			vread(buf, (char *)start, tsz);
>  			/* we have to zero-fill user buffer even if no read */

lgtm.  Let's add a nice little why-were-doing-this?

--- a/fs/proc/kcore.c~proc-kcore-fix-invalid-memory-access-in-multi-page-read-optimization-v3-fix
+++ a/fs/proc/kcore.c
@@ -464,7 +464,7 @@ read_kcore(struct file *file, char __use
 				ret = -EFAULT;
 				goto out;
 			}
-			m = NULL;
+			m = NULL;	/* skip the list anchor */
 		} else if (m->type == KCORE_VMALLOC) {
 			vread(buf, (char *)start, tsz);
 			/* we have to zero-fill user buffer even if no read */
_