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Fix incorrect user space access locking in mincore() (CVE-2006-4814)

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Doug Chapman noticed that mincore() will doa "copy_to_user()" of the
result while holding the mmap semaphore for reading, which is a big
no-no.  While a recursive read-lock on a semaphore in the case of a page
fault happens to work, we don't actually allow them due to deadlock
schenarios with writers due to fairness issues.

Doug and Marcel sent in a patch to fix it, but I decided to just rewrite
the mess instead - not just fixing the locking problem, but making the
code smaller and (imho) much easier to understand.

Also included are two fixes for the original patch including one
by Oleg Nesterov.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
This commit is contained in:
Linus Torvalds
2007-01-04 01:44:45 +01:00
committed by Adrian Bunk
parent 571525bb8f
commit 7c876d457b
1 changed files with 75 additions and 102 deletions
Download Patch File Download Diff File Expand all files Collapse all files
mm/mincore.c
+75 -102
View File
@@ -1,7 +1,7 @@
/*
* linux/mm/mincore.c
*
* Copyright (C) 1994-1999 Linus Torvalds
* Copyright (C) 1994-2006 Linus Torvalds
*/
/*
@@ -38,46 +38,51 @@ static unsigned char mincore_page(struct vm_area_struct * vma,
return present;
}
static long mincore_vma(struct vm_area_struct * vma,
unsigned long start, unsigned long end, unsigned char __user * vec)
/*
* Do a chunk of "sys_mincore()". We've already checked
* all the arguments, we hold the mmap semaphore: we should
* just return the amount of info we're asked for.
*/
static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages)
{
long error, i, remaining;
unsigned char * tmp;
unsigned long i, nr, pgoff;
struct vm_area_struct *vma = find_vma(current->mm, addr);
error = -ENOMEM;
/*
* find_vma() didn't find anything above us, or we're
* in an unmapped hole in the address space: ENOMEM.
*/
if (!vma || addr < vma->vm_start)
return -ENOMEM;
/*
* Ok, got it. But check whether it's a segment we support
* mincore() on. Right now, we don't do any anonymous mappings.
*
* FIXME: This is just stupid. And returning ENOMEM is
* stupid too. We should just look at the page tables. But
* this is what we've traditionally done, so we'll just
* continue doing it.
*/
if (!vma->vm_file)
return error;
return -ENOMEM;
start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
if (end > vma->vm_end)
end = vma->vm_end;
end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
/*
* Calculate how many pages there are left in the vma, and
* what the pgoff is for our address.
*/
nr = (vma->vm_end - addr) >> PAGE_SHIFT;
if (nr > pages)
nr = pages;
error = -EAGAIN;
tmp = (unsigned char *) __get_free_page(GFP_KERNEL);
if (!tmp)
return error;
pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
pgoff += vma->vm_pgoff;
/* (end - start) is # of pages, and also # of bytes in "vec */
remaining = (end - start),
/* And then we just fill the sucker in.. */
for (i = 0 ; i < nr; i++, pgoff++)
vec[i] = mincore_page(vma, pgoff);
error = 0;
for (i = 0; remaining > 0; remaining -= PAGE_SIZE, i++) {
int j = 0;
long thispiece = (remaining < PAGE_SIZE) ?
remaining : PAGE_SIZE;
while (j < thispiece)
tmp[j++] = mincore_page(vma, start++);
if (copy_to_user(vec + PAGE_SIZE * i, tmp, thispiece)) {
error = -EFAULT;
break;
}
}
free_page((unsigned long) tmp);
return error;
return nr;
}
/*
@@ -107,82 +112,50 @@ static long mincore_vma(struct vm_area_struct * vma,
asmlinkage long sys_mincore(unsigned long start, size_t len,
unsigned char __user * vec)
{
int index = 0;
unsigned long end, limit;
struct vm_area_struct * vma;
size_t max;
int unmapped_error = 0;
long error;
long retval;
unsigned long pages;
unsigned char *tmp;
/* check the arguments */
/* Check the start address: needs to be page-aligned.. */
if (start & ~PAGE_CACHE_MASK)
goto einval;
return -EINVAL;
limit = TASK_SIZE;
if (start >= limit)
goto enomem;
/* ..and we need to be passed a valid user-space range */
if (!access_ok(VERIFY_READ, (void __user *) start, len))
return -ENOMEM;
if (!len)
return 0;
/* This also avoids any overflows on PAGE_CACHE_ALIGN */
pages = len >> PAGE_SHIFT;
pages += (len & ~PAGE_MASK) != 0;
max = limit - start;
len = PAGE_CACHE_ALIGN(len);
if (len > max || !len)
goto enomem;
if (!access_ok(VERIFY_WRITE, vec, pages))
return -EFAULT;
end = start + len;
tmp = (void *) __get_free_page(GFP_USER);
if (!tmp)
return -EAGAIN;
/* check the output buffer whilst holding the lock */
error = -EFAULT;
down_read(&current->mm->mmap_sem);
retval = 0;
while (pages) {
/*
* Do at most PAGE_SIZE entries per iteration, due to
* the temporary buffer size.
*/
down_read(&current->mm->mmap_sem);
retval = do_mincore(start, tmp, min(pages, PAGE_SIZE));
up_read(&current->mm->mmap_sem);
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.
*/
error = 0;
vma = find_vma(current->mm, start);
while (vma) {
/* Here start < vma->vm_end. */
if (start < vma->vm_start) {
unmapped_error = -ENOMEM;
start = vma->vm_start;
if (retval <= 0)
break;
if (copy_to_user(vec, tmp, retval)) {
retval = -EFAULT;
break;
}
/* Here vma->vm_start <= start < vma->vm_end. */
if (end <= vma->vm_end) {
if (start < end) {
error = mincore_vma(vma, start, end,
&vec[index]);
if (error)
goto out;
}
error = unmapped_error;
goto out;
}
/* Here vma->vm_start <= start < vma->vm_end < end. */
error = mincore_vma(vma, start, vma->vm_end, &vec[index]);
if (error)
goto out;
index += (vma->vm_end - start) >> PAGE_CACHE_SHIFT;
start = vma->vm_end;
vma = vma->vm_next;
pages -= retval;
vec += retval;
start += retval << PAGE_SHIFT;
retval = 0;
}
/* 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;
free_page((unsigned long) tmp);
return retval;
}