Re: 2.6.13-mm3 [OOPS] vfs, page_owner, full reproductively, badness in vsnprintf

[Michal Piotrowski <michal.k.k.piotrowski@gmail.com>]

Hi,

On 12/09/05, Alexander Nyberg <alexn@telia.com> wrote:
> 
> Gah, I'm such a fantastic programmer.
> 
> I don't know what mc is up to but the error checking in read_page_owner
> is flawed wrt snprintf which could cause the 'size' argument to snprintf
> to become negative and if so overwrite beyond 'buf'.
> 
> Again, I fail to see how mc causes this to happen, but this fixes it
> by proper error checking.
> 
> Signed-off-by: Alexander Nyberg <alexn@telia.com>

Thanks, patch solved problem.
Here is version, that clean apply on 2.6.13-mm3. Can you review it?

Regards,
Michal Piotrowski

Signed-off-by: Michal K. K. Piotrowski <michal.k.k.piotrowski@gmail.com>

diff -uprN -X linux-mm-clean/Documentation/dontdiff
linux-mm-clean/fs/proc/proc_misc.c linux-mm/fs/proc/proc_misc.c
--- linux-mm-clean/fs/proc/proc_misc.c	2005-09-12 23:02:10.000000000 +0200
+++ linux-mm/fs/proc/proc_misc.c	2005-09-12 22:52:51.000000000 +0200
@@ -567,6 +567,7 @@ read_page_owner(struct file *file, char 
  	char namebuf[128];
  	unsigned long offset = 0, symsize;
 	int i;
+	ssize_t num_written = 0;
 
  	pfn = min_low_pfn + *ppos;
  	page = pfn_to_page(pfn);
@@ -587,23 +588,41 @@ read_page_owner(struct file *file, char 
  	kbuf = kmalloc(count, GFP_KERNEL);
  	if (!kbuf)
  		return -ENOMEM;
+        ret = snprintf(kbuf, count, "Page allocated via order %d,
mask 0x%x\n",                        page->order, page->gfp_mask);
+        if (ret >= count) {
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        num_written = ret;
 
-	ret = snprintf(kbuf, 1024, "Page allocated via order %d, mask 0x%x\n",
-			page->order, page->gfp_mask);
 
 	for (i = 0; i < 8; i++) {
 		if (!page->trace[i])
 			break;
  		symname = kallsyms_lookup(page->trace[i], &symsize, &offset,
&modname, namebuf);
-		ret += snprintf(kbuf + ret, count - ret, "[0x%lx] %s+%lu\n",
+                ret = snprintf(kbuf + num_written, count -
num_written, "[0x%lx] %s+%lu\n",
  			page->trace[i], namebuf, offset);
+                if (ret >= count - num_written) {
+                        ret = -ENOMEM;
+                        goto out;
+                }
+                num_written += ret;
+
 	}
+        ret = snprintf(kbuf + num_written, count - num_written, "\n");
+        if (ret >= count - num_written) {
+                ret = -ENOMEM;
+                goto out;
+        }
 
-	ret += snprintf(kbuf + ret, count -ret, "\n");
+        num_written += ret;
+        ret = num_written;
 
  	if (copy_to_user(buf, kbuf, ret))
  		ret = -EFAULT;
 
+out:
  	kfree(kbuf);
  	return ret;
 }
-
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