untangle the do_mremap() mess

This backports the following upstream commits all as one patch:
	54f5de709984bae0d31d823ff03de755f9dcac54
	ecc1a8993751de4e82eb18640d631dae1f626bd6
	1a0ef85f84feb13f07b604fcf5b90ef7c2b5c82f
	f106af4e90eadd76cfc0b5325f659619e08fb762
	097eed103862f9c6a97f2e415e21d1134017b135
	935874141df839c706cd6cdc438e85eb69d1525e
	0ec62d290912bb4b989be7563851bc364ec73b56
	c4caa778157dbbf04116f0ac2111e389b5cd7a29
	2ea1d13f64efdf49319e86c87d9ba38c30902782
	570dcf2c15463842e384eb597a87c1e39bead99b
	564b3bffc619dcbdd160de597b0547a7017ea010
	0067bd8a55862ac9dd212bd1c4f6f5bff1ca1301
	f8b7256096a20436f6d0926747e3ac3d64c81d24
	8c7b49b3ecd48923eb64ff57e07a1cdb74782970
	9206de95b1ea68357996ec02be5db0638a0de2c1
	2c6a10161d0b5fc047b5bd81b03693b9af99fab5
	05d72faa6d13c9d857478a5d35c85db9adada685
	bb52d6694002b9d632bb355f64daa045c6293a4e
	e77414e0aad6a1b063ba5e5750c582c75327ea6a
	aa65607373a4daf2010e8c3867b6317619f3c1a3

Backport done by Greg Kroah-Hartman.  Only minor tweaks were needed.

Cc: David S. Miller <davem@davemloft.net>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 156 insertions, 85 deletions

diff --git a/mm/mremap.c b/mm/mremap.c
index 97bff254771..845190898d5 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -261,6 +261,137 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	return new_addr;
 }
 
+static struct vm_area_struct *vma_to_resize(unsigned long addr,
+	unsigned long old_len, unsigned long new_len, unsigned long *p)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma = find_vma(mm, addr);
+
+	if (!vma || vma->vm_start > addr)
+		goto Efault;
+
+	if (is_vm_hugetlb_page(vma))
+		goto Einval;
+
+	/* We can't remap across vm area boundaries */
+	if (old_len > vma->vm_end - addr)
+		goto Efault;
+
+	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) {
+		if (new_len > old_len)
+			goto Efault;
+	}
+
+	if (vma->vm_flags & VM_LOCKED) {
+		unsigned long locked, lock_limit;
+		locked = mm->locked_vm << PAGE_SHIFT;
+		lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
+		locked += new_len - old_len;
+		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
+			goto Eagain;
+	}
+
+	if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
+		goto Enomem;
+
+	if (vma->vm_flags & VM_ACCOUNT) {
+		unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
+		if (security_vm_enough_memory(charged))
+			goto Efault;
+		*p = charged;
+	}
+
+	return vma;
+
+Efault:	/* very odd choice for most of the cases, but... */
+	return ERR_PTR(-EFAULT);
+Einval:
+	return ERR_PTR(-EINVAL);
+Enomem:
+	return ERR_PTR(-ENOMEM);
+Eagain:
+	return ERR_PTR(-EAGAIN);
+}
+
+static unsigned long mremap_to(unsigned long addr,
+	unsigned long old_len, unsigned long new_addr,
+	unsigned long new_len)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+	unsigned long ret = -EINVAL;
+	unsigned long charged = 0;
+	unsigned long map_flags;
+
+	if (new_addr & ~PAGE_MASK)
+		goto out;
+
+	if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
+		goto out;
+
+	/* Check if the location we're moving into overlaps the
+	 * old location at all, and fail if it does.
+	 */
+	if ((new_addr <= addr) && (new_addr+new_len) > addr)
+		goto out;
+
+	if ((addr <= new_addr) && (addr+old_len) > new_addr)
+		goto out;
+
+	ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
+	if (ret)
+		goto out;
+
+	ret = do_munmap(mm, new_addr, new_len);
+	if (ret)
+		goto out;
+
+	if (old_len >= new_len) {
+		ret = do_munmap(mm, addr+new_len, old_len - new_len);
+		if (ret && old_len != new_len)
+			goto out;
+		old_len = new_len;
+	}
+
+	vma = vma_to_resize(addr, old_len, new_len, &charged);
+	if (IS_ERR(vma)) {
+		ret = PTR_ERR(vma);
+		goto out;
+	}
+
+	map_flags = MAP_FIXED;
+	if (vma->vm_flags & VM_MAYSHARE)
+		map_flags |= MAP_SHARED;
+
+	ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
+				((addr - vma->vm_start) >> PAGE_SHIFT),
+				map_flags);
+	if (ret & ~PAGE_MASK)
+		goto out1;
+
+	ret = move_vma(vma, addr, old_len, new_len, new_addr);
+	if (!(ret & ~PAGE_MASK))
+		goto out;
+out1:
+	vm_unacct_memory(charged);
+
+out:
+	return ret;
+}
+
+static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
+{
+	unsigned long end = vma->vm_end + delta;
+	if (end < vma->vm_end) /* overflow */
+		return 0;
+	if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
+		return 0;
+	if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
+			      0, MAP_FIXED) & ~PAGE_MASK)
+		return 0;
+	return 1;
+}
+
 /*
  * Expand (or shrink) an existing mapping, potentially moving it at the
  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
@@ -294,32 +425,10 @@ unsigned long do_mremap(unsigned long addr,
 	if (!new_len)
 		goto out;
 
-	/* new_addr is only valid if MREMAP_FIXED is specified */
 	if (flags & MREMAP_FIXED) {
-		if (new_addr & ~PAGE_MASK)
-			goto out;
-		if (!(flags & MREMAP_MAYMOVE))
-			goto out;
-
-		if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
-			goto out;
-
-		/* Check if the location we're moving into overlaps the
-		 * old location at all, and fail if it does.
-		 */
-		if ((new_addr <= addr) && (new_addr+new_len) > addr)
-			goto out;
-
-		if ((addr <= new_addr) && (addr+old_len) > new_addr)
-			goto out;
-
-		ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
-		if (ret)
-			goto out;
-
-		ret = do_munmap(mm, new_addr, new_len);
-		if (ret)
-			goto out;
+		if (flags & MREMAP_MAYMOVE)
+			ret = mremap_to(addr, old_len, new_addr, new_len);
+		goto out;
 	}
 
 	/*
@@ -332,60 +441,23 @@ unsigned long do_mremap(unsigned long addr,
 		if (ret && old_len != new_len)
 			goto out;
 		ret = addr;
-		if (!(flags & MREMAP_FIXED) || (new_addr == addr))
-			goto out;
-		old_len = new_len;
+		goto out;
 	}
 
 	/*
-	 * Ok, we need to grow..  or relocate.
+	 * Ok, we need to grow..
 	 */
-	ret = -EFAULT;
-	vma = find_vma(mm, addr);
-	if (!vma || vma->vm_start > addr)
-		goto out;
-	if (is_vm_hugetlb_page(vma)) {
-		ret = -EINVAL;
-		goto out;
-	}
-	/* We can't remap across vm area boundaries */
-	if (old_len > vma->vm_end - addr)
-		goto out;
-	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) {
-		if (new_len > old_len)
-			goto out;
-	}
-	if (vma->vm_flags & VM_LOCKED) {
-		unsigned long locked, lock_limit;
-		locked = mm->locked_vm << PAGE_SHIFT;
-		lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
-		locked += new_len - old_len;
-		ret = -EAGAIN;
-		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
-			goto out;
-	}
-	if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT)) {
-		ret = -ENOMEM;
+	vma = vma_to_resize(addr, old_len, new_len, &charged);
+	if (IS_ERR(vma)) {
+		ret = PTR_ERR(vma);
 		goto out;
 	}
 
-	if (vma->vm_flags & VM_ACCOUNT) {
-		charged = (new_len - old_len) >> PAGE_SHIFT;
-		if (security_vm_enough_memory(charged))
-			goto out_nc;
-	}
-
 	/* old_len exactly to the end of the area..
-	 * And we're not relocating the area.
 	 */
-	if (old_len == vma->vm_end - addr &&
-	    !((flags & MREMAP_FIXED) && (addr != new_addr)) &&
-	    (old_len != new_len || !(flags & MREMAP_MAYMOVE))) {
-		unsigned long max_addr = TASK_SIZE;
-		if (vma->vm_next)
-			max_addr = vma->vm_next->vm_start;
+	if (old_len == vma->vm_end - addr) {
 		/* can we just expand the current mapping? */
-		if (max_addr - addr >= new_len) {
+		if (vma_expandable(vma, new_len - old_len)) {
 			int pages = (new_len - old_len) >> PAGE_SHIFT;
 
 			vma_adjust(vma, vma->vm_start,
@@ -409,28 +481,27 @@ unsigned long do_mremap(unsigned long addr,
 	 */
 	ret = -ENOMEM;
 	if (flags & MREMAP_MAYMOVE) {
-		if (!(flags & MREMAP_FIXED)) {
-			unsigned long map_flags = 0;
-			if (vma->vm_flags & VM_MAYSHARE)
-				map_flags |= MAP_SHARED;
-
-			new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
-						vma->vm_pgoff, map_flags);
-			if (new_addr & ~PAGE_MASK) {
-				ret = new_addr;
-				goto out;
-			}
-
-			ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
-			if (ret)
-				goto out;
+		unsigned long map_flags = 0;
+		if (vma->vm_flags & VM_MAYSHARE)
+			map_flags |= MAP_SHARED;
+
+		new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
+					vma->vm_pgoff +
+					((addr - vma->vm_start) >> PAGE_SHIFT),
+					map_flags);
+		if (new_addr & ~PAGE_MASK) {
+			ret = new_addr;
+			goto out;
 		}
+
+		ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
+		if (ret)
+			goto out;
 		ret = move_vma(vma, addr, old_len, new_len, new_addr);
 	}
 out:
 	if (ret & ~PAGE_MASK)
 		vm_unacct_memory(charged);
-out_nc:
 	return ret;
 }