mm: madvise: complete input validation before taking lock

In madvise(), there doesn't seem to be any reason for taking the
&current->mm->mmap_sem before start and len_in have been validated.
Incidentally, this removes the need for the out: label.

[akpm@linux-foundation.org: s/out_plug/out/, per David]
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/madvise.c b/mm/madvise.c
index c58c94b..7055883 100644 (file)
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -473,27 +473,27 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
        if (!madvise_behavior_valid(behavior))
                return error;
 
-       write = madvise_need_mmap_write(behavior);
-       if (write)
-               down_write(&current->mm->mmap_sem);
-       else
-               down_read(&current->mm->mmap_sem);
-
        if (start & ~PAGE_MASK)
-               goto out;
+               return error;
        len = (len_in + ~PAGE_MASK) & PAGE_MASK;
 
        /* Check to see whether len was rounded up from small -ve to zero */
        if (len_in && !len)
-               goto out;
+               return error;
 
        end = start + len;
        if (end < start)
-               goto out;
+               return error;
 
        error = 0;
        if (end == start)
-               goto out;
+               return error;
+
+       write = madvise_need_mmap_write(behavior);
+       if (write)
+               down_write(&current->mm->mmap_sem);
+       else
+               down_read(&current->mm->mmap_sem);
 
        /*
         * If the interval [start,end) covers some unmapped address
@@ -509,14 +509,14 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
                /* Still start < end. */
                error = -ENOMEM;
                if (!vma)
-                       goto out_plug;
+                       goto out;
 
                /* Here start < (end|vma->vm_end). */
                if (start < vma->vm_start) {
                        unmapped_error = -ENOMEM;
                        start = vma->vm_start;
                        if (start >= end)
-                               goto out_plug;
+                               goto out;
                }
 
                /* Here vma->vm_start <= start < (end|vma->vm_end) */
@@ -527,21 +527,20 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
                /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
                error = madvise_vma(vma, &prev, start, tmp, behavior);
                if (error)
-                       goto out_plug;
+                       goto out;
                start = tmp;
                if (prev && start < prev->vm_end)
                        start = prev->vm_end;
                error = unmapped_error;
                if (start >= end)
-                       goto out_plug;
+                       goto out;
                if (prev)
                        vma = prev->vm_next;
                else    /* madvise_remove dropped mmap_sem */
                        vma = find_vma(current->mm, start);
        }
-out_plug:
-       blk_finish_plug(&plug);
 out:
+       blk_finish_plug(&plug);
        if (write)
                up_write(&current->mm->mmap_sem);
        else