[PATCH] xacct_add_tsk: fix pure theoretical ->mm use-after-free

Paranoid fix. The task can free its ->mm after the 'if (p->mm)' check.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Jay Lan <jlan@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index 65a5036..96f7701 100644 (file)
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -80,13 +80,17 @@ void bacct_add_tsk(struct taskstats *stats, struct task_struct *tsk)
  */
 void xacct_add_tsk(struct taskstats *stats, struct task_struct *p)
 {
+       struct mm_struct *mm;
+
        /* convert pages-jiffies to Mbyte-usec */
        stats->coremem = jiffies_to_usecs(p->acct_rss_mem1) * PAGE_SIZE / MB;
        stats->virtmem = jiffies_to_usecs(p->acct_vm_mem1) * PAGE_SIZE / MB;
-       if (p->mm) {
+       mm = get_task_mm(p);
+       if (mm) {
                /* adjust to KB unit */
-               stats->hiwater_rss   = p->mm->hiwater_rss * PAGE_SIZE / KB;
-               stats->hiwater_vm    = p->mm->hiwater_vm * PAGE_SIZE / KB;
+               stats->hiwater_rss   = mm->hiwater_rss * PAGE_SIZE / KB;
+               stats->hiwater_vm    = mm->hiwater_vm * PAGE_SIZE / KB;
+               mmput(mm);
        }
        stats->read_char        = p->rchar;
        stats->write_char       = p->wchar;