fs/proc/task_mmu.c: fix buffer overflow in add_page_map()

commit 8c8296223f3abb142be8fc31711b18a704c0e7d8 upstream.

Recently we met quite a lot of random kernel panic issues after enabling
CONFIG_PROC_PAGE_MONITOR.  After debuggind we found this has something
to do with following bug in pagemap:

In struct 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.

[akpm@linux-foundation.org: document pagemapread.pos and .len units, fix PM_ENTRY_BYTES definition]
Signed-off-by: Yonghua Zheng <younghua.zheng@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2:
 - Adjust context
 - There is no pagemap_entry_t definition; keep using u64]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 3efa725..ef1740d 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -604,7 +604,7 @@ const struct file_operations proc_clear_refs_operations = {
 };
 
 struct pagemapread {
-       int pos, len;
+       int pos, len;           /* units: PM_ENTRY_BYTES, not bytes */
        u64 *buffer;
 };
 
@@ -792,8 +792,8 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
        if (!count)
                goto out_task;
 
-       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;