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SubjectRe: [PATCH 1/1] pagemap: fix buffer overflow in add_page_map()
On Fri, 9 Aug 2013 13:16:41 +0800 yonghua zheng <younghua.zheng@gmail.com> wrote:

> Hi,
>
> Recently we met quite a lot of random kernel panic issues after enable
> CONFIG_PROC_PAGE_MONITOR in kernel, after debuggint sometime we found
> this has something to do with following bug in pagemap:
>
> In struc pagemapread:
>
> struct pagemapread {
> int pos, len;
> pagemap_entry_t *buffer;
> bool v2;
> };
>
> pos is number of PM_ENTRY_BYTES in buffer, but len is the size of buffer,
> it is a mistake to compare pos and len in add_page_map() for checking
> buffer is full or not, and this can lead to buffer overflow and random
> kernel panic issue.
>
> Correct len to be total number of PM_ENTRY_BYTES in buffer.
>
> Signed-off-by: Yonghua Zheng <younghua.zheng@gmail.com>
> ---
> fs/proc/task_mmu.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index dbf61f6..cb98853 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1116,8 +1116,8 @@ static ssize_t pagemap_read(struct file *file,
> char __user *buf,
> goto out_task;
>
> pm.v2 = soft_dirty_cleared;
> - pm.len = PM_ENTRY_BYTES * (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
> - pm.buffer = kmalloc(pm.len, GFP_TEMPORARY);
> + pm.len = (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
> + pm.buffer = kmalloc(pm.len * PM_ENTRY_BYTES, GFP_TEMPORARY);
> ret = -ENOMEM;
> if (!pm.buffer)
> goto out_task;

Yes, that's a bug. I'd propose this addition to your fix:

From: Andrew Morton <akpm@linux-foundation.org>
Subject: pagemap-fix-buffer-overflow-in-add_page_map-fix

document pagemapread.pos and .len units, fix PM_ENTRY_BYTES definition

Cc: Yonghua Zheng <younghua.zheng@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

fs/proc/task_mmu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff -puN fs/proc/task_mmu.c~pagemap-fix-buffer-overflow-in-add_page_map-fix fs/proc/task_mmu.c
--- a/fs/proc/task_mmu.c~pagemap-fix-buffer-overflow-in-add_page_map-fix
+++ a/fs/proc/task_mmu.c
@@ -868,7 +868,7 @@ typedef struct {
} pagemap_entry_t;

struct pagemapread {
- int pos, len;
+ int pos, len; /* units: PM_ENTRY_BYTES, not bytes */
pagemap_entry_t *buffer;
bool v2;
};
@@ -876,7 +876,7 @@ struct pagemapread {
#define PAGEMAP_WALK_SIZE (PMD_SIZE)
#define PAGEMAP_WALK_MASK (PMD_MASK)

-#define PM_ENTRY_BYTES sizeof(u64)
+#define PM_ENTRY_BYTES sizeof(pagemap_entry_t)
#define PM_STATUS_BITS 3
#define PM_STATUS_OFFSET (64 - PM_STATUS_BITS)
#define PM_STATUS_MASK (((1LL << PM_STATUS_BITS) - 1) << PM_STATUS_OFFSET)
_

btw, your email client wordwraps the patches and replaces tabs with
spaces. Please fix that up for next time?



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