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Fix incorrect user space access locking in mincore()
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. Cc: Doug Chapman <dchapman@redhat.com> Cc: Marcel Holtmann <holtmann@redhat.com> Cc: Hugh Dickins <hugh@veritas.com> Cc: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Linus Torvalds
parent
0221872a3b
commit
2f77d10705
192
mm/mincore.c
192
mm/mincore.c
@ -1,7 +1,7 @@
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/*
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* linux/mm/mincore.c
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*
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* Copyright (C) 1994-1999 Linus Torvalds
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* Copyright (C) 1994-2006 Linus Torvalds
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*/
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/*
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@ -38,46 +38,60 @@ static unsigned char mincore_page(struct vm_area_struct * vma,
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return present;
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}
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static long mincore_vma(struct vm_area_struct * vma,
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unsigned long start, unsigned long end, unsigned char __user * vec)
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/*
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* Do a chunk of "sys_mincore()". We've already checked
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* all the arguments, we hold the mmap semaphore: we should
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* just return the amount of info we're asked for.
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*/
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static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages)
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{
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long error, i, remaining;
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unsigned char * tmp;
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unsigned long i, nr, pgoff;
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struct vm_area_struct *vma = find_vma(current->mm, addr);
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error = -ENOMEM;
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if (!vma->vm_file)
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return error;
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start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
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if (end > vma->vm_end)
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end = vma->vm_end;
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end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
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error = -EAGAIN;
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tmp = (unsigned char *) __get_free_page(GFP_KERNEL);
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if (!tmp)
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return error;
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/* (end - start) is # of pages, and also # of bytes in "vec */
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remaining = (end - start),
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error = 0;
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for (i = 0; remaining > 0; remaining -= PAGE_SIZE, i++) {
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int j = 0;
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long thispiece = (remaining < PAGE_SIZE) ?
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remaining : PAGE_SIZE;
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while (j < thispiece)
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tmp[j++] = mincore_page(vma, start++);
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if (copy_to_user(vec + PAGE_SIZE * i, tmp, thispiece)) {
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error = -EFAULT;
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break;
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}
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/*
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* find_vma() didn't find anything: the address
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* is above everything we have mapped.
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*/
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if (!vma) {
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memset(vec, 0, pages);
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return pages;
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}
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free_page((unsigned long) tmp);
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return error;
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/*
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* find_vma() found something, but we might be
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* below it: check for that.
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*/
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if (addr < vma->vm_start) {
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unsigned long gap = (vma->vm_start - addr) >> PAGE_SHIFT;
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if (gap > pages)
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gap = pages;
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memset(vec, 0, gap);
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return gap;
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}
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/*
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* Ok, got it. But check whether it's a segment we support
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* mincore() on. Right now, we don't do any anonymous mappings.
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*/
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if (!vma->vm_file)
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return -ENOMEM;
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/*
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* Calculate how many pages there are left in the vma, and
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* what the pgoff is for our address.
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*/
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nr = (vma->vm_end - addr) >> PAGE_SHIFT;
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if (nr > pages)
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nr = pages;
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pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
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pgoff += vma->vm_pgoff;
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/* And then we just fill the sucker in.. */
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for (i = 0 ; i < nr; i++, pgoff++)
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vec[i] = mincore_page(vma, pgoff);
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return nr;
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}
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/*
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@ -107,82 +121,50 @@ static long mincore_vma(struct vm_area_struct * vma,
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asmlinkage long sys_mincore(unsigned long start, size_t len,
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unsigned char __user * vec)
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{
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int index = 0;
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unsigned long end, limit;
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struct vm_area_struct * vma;
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size_t max;
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int unmapped_error = 0;
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long error;
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long retval;
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unsigned long pages;
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unsigned char *tmp;
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/* check the arguments */
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/* Check the start address: needs to be page-aligned.. */
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if (start & ~PAGE_CACHE_MASK)
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goto einval;
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return -EINVAL;
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limit = TASK_SIZE;
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if (start >= limit)
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goto enomem;
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/* ..and we need to be passed a valid user-space range */
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if (!access_ok(VERIFY_READ, (void __user *) start, len))
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return -ENOMEM;
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if (!len)
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return 0;
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/* This also avoids any overflows on PAGE_CACHE_ALIGN */
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pages = len >> PAGE_SHIFT;
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pages += (len & ~PAGE_MASK) != 0;
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max = limit - start;
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len = PAGE_CACHE_ALIGN(len);
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if (len > max || !len)
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goto enomem;
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if (!access_ok(VERIFY_WRITE, vec, pages))
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return -EFAULT;
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end = start + len;
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tmp = (void *) __get_free_page(GFP_USER);
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if (!tmp)
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return -ENOMEM;
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/* check the output buffer whilst holding the lock */
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error = -EFAULT;
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down_read(¤t->mm->mmap_sem);
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retval = 0;
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while (pages) {
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/*
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* Do at most PAGE_SIZE entries per iteration, due to
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* the temporary buffer size.
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*/
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down_read(¤t->mm->mmap_sem);
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retval = do_mincore(start, tmp, max(pages, PAGE_SIZE));
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up_read(¤t->mm->mmap_sem);
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if (!access_ok(VERIFY_WRITE, vec, len >> PAGE_SHIFT))
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goto out;
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/*
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* If the interval [start,end) covers some unmapped address
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* ranges, just ignore them, but return -ENOMEM at the end.
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*/
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error = 0;
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vma = find_vma(current->mm, start);
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while (vma) {
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/* Here start < vma->vm_end. */
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if (start < vma->vm_start) {
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unmapped_error = -ENOMEM;
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start = vma->vm_start;
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if (retval <= 0)
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break;
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if (copy_to_user(vec, tmp, retval)) {
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retval = -EFAULT;
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break;
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}
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/* Here vma->vm_start <= start < vma->vm_end. */
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if (end <= vma->vm_end) {
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if (start < end) {
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error = mincore_vma(vma, start, end,
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&vec[index]);
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if (error)
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goto out;
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}
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error = unmapped_error;
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goto out;
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}
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/* Here vma->vm_start <= start < vma->vm_end < end. */
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error = mincore_vma(vma, start, vma->vm_end, &vec[index]);
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if (error)
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goto out;
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index += (vma->vm_end - start) >> PAGE_CACHE_SHIFT;
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start = vma->vm_end;
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vma = vma->vm_next;
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pages -= retval;
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vec += retval;
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start += retval << PAGE_SHIFT;
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retval = 0;
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}
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/* we found a hole in the area queried if we arrive here */
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error = -ENOMEM;
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out:
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up_read(¤t->mm->mmap_sem);
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return error;
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einval:
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return -EINVAL;
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enomem:
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return -ENOMEM;
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free_page((unsigned long) tmp);
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return retval;
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}
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