[PATCH] RLIMIT_AS checking fix

Address bug #4508: there's potential for wraparound in the various places
where we perform RLIMIT_AS checking.

(I'm a bit worried about acct_stack_growth().  Are we sure that vma->vm_mm is
always equal to current->mm?  If not, then we're comparing some other
process's total_vm with the calling process's rlimits).

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 19 insertions, 5 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 6ea204cc751e..1ec0f6e9c0d8 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1009,8 +1009,7 @@ munmap_back:
         }
 
         /* Check against address space limit. */
-        if ((mm->total_vm << PAGE_SHIFT) + len
-            > current->signal->rlim[RLIMIT_AS].rlim_cur)
+        if (!may_expand_vm(mm, len >> PAGE_SHIFT))
                 return -ENOMEM;
 
         if (accountable && (!(flags & MAP_NORESERVE) ||
@@ -1421,7 +1420,7 @@ static int acct_stack_growth(struct vm_area_struct * vma, unsigned long size, un
         struct rlimit *rlim = current->signal->rlim;
 
         /* address space limit tests */
-        if (mm->total_vm + grow > rlim[RLIMIT_AS].rlim_cur >> PAGE_SHIFT)
+        if (!may_expand_vm(mm, grow))
                 return -ENOMEM;
 
         /* Stack limit test */
@@ -1848,8 +1847,7 @@ unsigned long do_brk(unsigned long addr, unsigned long len)
         }
 
         /* Check against address space limits *after* clearing old maps... */
-        if ((mm->total_vm << PAGE_SHIFT) + len
-            > current->signal->rlim[RLIMIT_AS].rlim_cur)
+        if (!may_expand_vm(mm, len >> PAGE_SHIFT))
                 return -ENOMEM;
 
         if (mm->map_count > sysctl_max_map_count)
@@ -2019,3 +2017,19 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
         }
         return new_vma;
 }
+
+/*
+ * Return true if the calling process may expand its vm space by the passed
+ * number of pages
+ */
+int may_expand_vm(struct mm_struct *mm, unsigned long npages)
+{
+        unsigned long cur = mm->total_vm;       /* pages */
+        unsigned long lim;
+
+        lim = current->signal->rlim[RLIMIT_AS].rlim_cur >> PAGE_SHIFT;
+
+        if (cur + npages > lim)
+                return 0;
+        return 1;
+}