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

Michal Piotrowski
2005-09-12T21:13:26Z

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;
}