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SubjectRe: [patch] VM_IO fixes
On Wed, 6 Feb 2002, Andrew Morton wrote:
> This patch doesn't fix the PTRACE_PEEKUSR bug - for that we need
> this patch as well as the patch Andrea, Manfred and I pieced
> together - it's at http://www.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.18pre7aa2/00_get_user_pages-2
> I understand that Manfred will be sending you a version of that patch.
>
My patch is below.
The only difference between my and Andrea's version is one indentation and
a new comment that warns about possible cache coherency problems.

Tested only on i386 with -pre9, the PTRACE_PEEKUSR oops is fixed (ok, I've
tested pread from /proc/pid/mem, but that's the same code)

--
Manfred
<<<<<<<<<<<<<
--- 2.4/mm/memory.c Tue Dec 25 17:12:07 2001
+++ build-2.4/mm/memory.c Thu Feb 7 21:53:32 2002
@@ -442,6 +442,13 @@
return page;
}

+/*
+ * Please read Documentation/cachetlb.txt before using this function,
+ * accessing foreign memory spaces can cause cache coherency problems.
+ *
+ * Accessing a VM_IO area is even more dangerous, therefore the function
+ * fails if pages is != NULL and a VM_IO area is found.
+ */
int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start,
int len, int write, int force, struct page **pages, struct vm_area_struct **vmas)
{
@@ -453,6 +460,7 @@
vma = find_extend_vma(mm, start);

if ( !vma ||
+ (pages && vma->vm_flags & VM_IO) ||
(!force &&
((write && (!(vma->vm_flags & VM_WRITE))) ||
(!write && (!(vma->vm_flags & VM_READ))) ) )) {
@@ -486,8 +494,9 @@
/* FIXME: call the correct function,
* depending on the type of the found page
*/
- if (pages[i])
- page_cache_get(pages[i]);
+ if (!pages[i])
+ goto bad_page;
+ page_cache_get(pages[i]);
}
if (vmas)
vmas[i] = vma;
@@ -497,7 +506,19 @@
} while(len && start < vma->vm_end);
spin_unlock(&mm->page_table_lock);
} while(len);
+out:
return i;
+
+ /*
+ * We found an invalid page in the VMA. Release all we have
+ * so far and fail.
+ */
+bad_page:
+ spin_unlock(&mm->page_table_lock);
+ while (i--)
+ page_cache_release(pages[i]);
+ i = -EFAULT;
+ goto out;
}

/*
<<<<<<<<<<
-
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