[PATCH] Fix the mincore() syscall

[David Howells]

The attached patch fixes the mincore syscall in three ways:

 (1) It moves as much argument checking outside of the semaphore-holding
     region as possible.

 (2) It checks the region parameters against TASK_SIZE so that a 32-bit binary
     on a 64-bit platform will get the right error when calling this syscall
     on a region that overlaps the end of the 32-bit address space.

 (3) It tidies up the VMA checking loop a little.

Signed-Off-By: David Howells <[EMAIL PROTECTED]>
---
warthog>diffstat mincore-2611rc3bk8.diff 
 mincore.c |   50 ++++++++++++++++++++++++++++++++------------------
 1 files changed, 32 insertions(+), 18 deletions(-)

diff -uNrp linux-2.6.11-rc3-bk8/mm/mincore.c 
linux-2.6.11-rc3-bk8-mincore/mm/mincore.c
--- linux-2.6.11-rc3-bk8/mm/mincore.c   2005-01-04 11:13:57.000000000 +0000
+++ linux-2.6.11-rc3-bk8-mincore/mm/mincore.c   2005-02-11 18:44:25.563625998 
+0000
@@ -109,39 +109,45 @@ asmlinkage long sys_mincore(unsigned lon
        unsigned char __user * vec)
 {
        int index = 0;
-       unsigned long end;
+       unsigned long end, limit;
        struct vm_area_struct * vma;
+       size_t max;
        int unmapped_error = 0;
-       long error = -EINVAL;
+       long error;
 
-       down_read(&current->mm->mmap_sem);
+       /* check the arguments */
+       if (start & ~PAGE_CACHE_MASK)
+               goto einval;
+
+       if (start < FIRST_USER_PGD_NR * PGDIR_SIZE)
+               goto enomem;
+
+       limit = TASK_SIZE;
+       if (start >= limit)
+               goto enomem;
+
+       max = limit - start;
+       len = PAGE_CACHE_ALIGN(len);
+       if (len > max)
+               goto einval;
 
-       if (start & ~PAGE_CACHE_MASK)
-               goto out;
-       len = (len + ~PAGE_CACHE_MASK) & PAGE_CACHE_MASK;
        end = start + len;
-       if (end < start)
-               goto out;
 
+       /* check the output buffer whilst holding the lock */
        error = -EFAULT;
-       if (!access_ok(VERIFY_WRITE, vec, len >> PAGE_SHIFT))
-               goto out;
+       down_read(&current->mm->mmap_sem);
 
-       error = 0;
-       if (end == start)
+       if (!access_ok(VERIFY_WRITE, vec, len >> PAGE_SHIFT))
                goto out;
 
        /*
         * If the interval [start,end) covers some unmapped address
         * ranges, just ignore them, but return -ENOMEM at the end.
         */
-       vma = find_vma(current->mm, start);
-       for (;;) {
-               /* Still start < end. */
-               error = -ENOMEM;
-               if (!vma)
-                       goto out;
+       error = 0;
 
+       vma = find_vma(current->mm, start);
+       while (vma) {
                /* Here start < vma->vm_end. */
                if (start < vma->vm_start) {
                        unmapped_error = -ENOMEM;
@@ -169,7 +175,15 @@ asmlinkage long sys_mincore(unsigned lon
                vma = vma->vm_next;
        }
 
+       /* we found a hole in the area queried if we arrive here */
+       error = -ENOMEM;
+
 out:
        up_read(&current->mm->mmap_sem);
        return error;
+
+einval:
+       return -EINVAL;
+enomem:
+       return -ENOMEM;
 }
-
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