Commit 9b2301bf authored by Lorenzo Stoakes's avatar Lorenzo Stoakes Committed by Andrew Morton
Browse files

mm/mremap: move remap_is_valid() into check_prep_vma() 

Group parameter check logic together, moving check_mremap_params() next to
it.

This puts all such checks into a single place, and invokes them early so
we can simply bail out as soon as we are aware that a condition is not
met.

No functional change intended.

Link: https://lkml.kernel.org/r/4d0669c23531629d8ead42aa701c6237bd6bf012.1752770784.git.lorenzo.stoakes@oracle.com


Signed-off-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent a85dc371

mm/mremap.c

+138 −149
Original line number Diff line number Diff line
@@ -1306,71 +1306,6 @@ static unsigned long move_vma(struct vma_remap_struct *vrm) 
	return err ? (unsigned long)err : vrm->new_addr;

}



/*

 * remap_is_valid() - Ensure the VMA can be moved or resized to the new length,

 * at the given address.

 *

 * Return 0 on success, error otherwise.

 */

static int remap_is_valid(struct vma_remap_struct *vrm)

{

	struct mm_struct *mm = current->mm;

	struct vm_area_struct *vma = vrm->vma;

	unsigned long addr = vrm->addr;

	unsigned long old_len = vrm->old_len;

	unsigned long new_len = vrm->new_len;

	unsigned long pgoff;



	/*

	 * !old_len is a special case where an attempt is made to 'duplicate'

	 * a mapping.  This makes no sense for private mappings as it will

	 * instead create a fresh/new mapping unrelated to the original.  This

	 * is contrary to the basic idea of mremap which creates new mappings

	 * based on the original.  There are no known use cases for this

	 * behavior.  As a result, fail such attempts.

	 */

	if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {

		pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n",

			     current->comm, current->pid);

		return -EINVAL;

	}



	if ((vrm->flags & MREMAP_DONTUNMAP) &&

			(vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)))

		return -EINVAL;



	/*

	 * We permit crossing of boundaries for the range being unmapped due to

	 * a shrink.

	 */

	if (vrm->remap_type == MREMAP_SHRINK)

		old_len = new_len;



	/* We can't remap across vm area boundaries */

	if (old_len > vma->vm_end - addr)

		return -EFAULT;



	if (new_len == old_len)

		return 0;



	/* Need to be careful about a growing mapping */

	pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;

	pgoff += vma->vm_pgoff;

	if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)

		return -EINVAL;



	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))

		return -EFAULT;



	if (!mlock_future_ok(mm, vma->vm_flags, vrm->delta))

		return -EAGAIN;



	if (!may_expand_vm(mm, vma->vm_flags, vrm->delta >> PAGE_SHIFT))

		return -ENOMEM;



	return 0;

}



/*

 * The user has requested that the VMA be shrunk (i.e., old_len > new_len), so

 * execute this, optionally dropping the mmap lock when we do so.
@@ -1497,77 +1432,6 @@ static bool vrm_can_expand_in_place(struct vma_remap_struct *vrm) 
	return true;

}



/*

 * Are the parameters passed to mremap() valid? If so return 0, otherwise return

 * error.

 */

static unsigned long check_mremap_params(struct vma_remap_struct *vrm)



{

	unsigned long addr = vrm->addr;

	unsigned long flags = vrm->flags;



	/* Ensure no unexpected flag values. */

	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))

		return -EINVAL;



	/* Start address must be page-aligned. */

	if (offset_in_page(addr))

		return -EINVAL;



	/*

	 * We allow a zero old-len as a special case

	 * for DOS-emu "duplicate shm area" thing. But

	 * a zero new-len is nonsensical.

	 */

	if (!vrm->new_len)

		return -EINVAL;



	/* Is the new length or address silly? */

	if (vrm->new_len > TASK_SIZE ||

	    vrm->new_addr > TASK_SIZE - vrm->new_len)

		return -EINVAL;



	/* Remainder of checks are for cases with specific new_addr. */

	if (!vrm_implies_new_addr(vrm))

		return 0;



	/* The new address must be page-aligned. */

	if (offset_in_page(vrm->new_addr))

		return -EINVAL;



	/* A fixed address implies a move. */

	if (!(flags & MREMAP_MAYMOVE))

		return -EINVAL;



	/* MREMAP_DONTUNMAP does not allow resizing in the process. */

	if (flags & MREMAP_DONTUNMAP && vrm->old_len != vrm->new_len)

		return -EINVAL;



	/* Target VMA must not overlap source VMA. */

	if (vrm_overlaps(vrm))

		return -EINVAL;



	/*

	 * move_vma() need us to stay 4 maps below the threshold, otherwise

	 * it will bail out at the very beginning.

	 * That is a problem if we have already unmaped the regions here

	 * (new_addr, and old_addr), because userspace will not know the

	 * state of the vma's after it gets -ENOMEM.

	 * So, to avoid such scenario we can pre-compute if the whole

	 * operation has high chances to success map-wise.

	 * Worst-scenario case is when both vma's (new_addr and old_addr) get

	 * split in 3 before unmapping it.

	 * That means 2 more maps (1 for each) to the ones we already hold.

	 * Check whether current map count plus 2 still leads us to 4 maps below

	 * the threshold, otherwise return -ENOMEM here to be more safe.

	 */

	if ((current->mm->map_count + 2) >= sysctl_max_map_count - 3)

		return -ENOMEM;



	return 0;

}



/*

 * We know we can expand the VMA in-place by delta pages, so do so.

 *
@@ -1719,9 +1583,26 @@ static bool vrm_will_map_new(struct vma_remap_struct *vrm) 
	return false;

}



static void notify_uffd(struct vma_remap_struct *vrm, bool failed)

{

	struct mm_struct *mm = current->mm;



	/* Regardless of success/failure, we always notify of any unmaps. */

	userfaultfd_unmap_complete(mm, vrm->uf_unmap_early);

	if (failed)

		mremap_userfaultfd_fail(vrm->uf);

	else

		mremap_userfaultfd_complete(vrm->uf, vrm->addr,

			vrm->new_addr, vrm->old_len);

	userfaultfd_unmap_complete(mm, vrm->uf_unmap);

}



static int check_prep_vma(struct vma_remap_struct *vrm)

{

	struct vm_area_struct *vma = vrm->vma;

	struct mm_struct *mm = current->mm;

	unsigned long addr = vrm->addr;

	unsigned long old_len, new_len, pgoff;



	if (!vma)

		return -EFAULT;
@@ -1738,26 +1619,134 @@ static int check_prep_vma(struct vma_remap_struct *vrm) 
	vrm->remap_type = vrm_remap_type(vrm);

	/* For convenience, we set new_addr even if VMA won't move. */

	if (!vrm_implies_new_addr(vrm))

		vrm->new_addr = vrm->addr;

		vrm->new_addr = addr;



	/* Below only meaningful if we expand or move a VMA. */

	if (!vrm_will_map_new(vrm))

		return 0;



	old_len = vrm->old_len;

	new_len = vrm->new_len;



	/*

	 * !old_len is a special case where an attempt is made to 'duplicate'

	 * a mapping.  This makes no sense for private mappings as it will

	 * instead create a fresh/new mapping unrelated to the original.  This

	 * is contrary to the basic idea of mremap which creates new mappings

	 * based on the original.  There are no known use cases for this

	 * behavior.  As a result, fail such attempts.

	 */

	if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {

		pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n",

			     current->comm, current->pid);

		return -EINVAL;

	}



	if ((vrm->flags & MREMAP_DONTUNMAP) &&

			(vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)))

		return -EINVAL;



	/*

	 * We permit crossing of boundaries for the range being unmapped due to

	 * a shrink.

	 */

	if (vrm->remap_type == MREMAP_SHRINK)

		old_len = new_len;



	/* We can't remap across vm area boundaries */

	if (old_len > vma->vm_end - addr)

		return -EFAULT;



	if (new_len == old_len)

		return 0;



	/* Need to be careful about a growing mapping */

	pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;

	pgoff += vma->vm_pgoff;

	if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)

		return -EINVAL;



	if (vrm_will_map_new(vrm))

		return remap_is_valid(vrm);

	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))

		return -EFAULT;



	if (!mlock_future_ok(mm, vma->vm_flags, vrm->delta))

		return -EAGAIN;



	if (!may_expand_vm(mm, vma->vm_flags, vrm->delta >> PAGE_SHIFT))

		return -ENOMEM;



	return 0;

}



static void notify_uffd(struct vma_remap_struct *vrm, bool failed)

/*

 * Are the parameters passed to mremap() valid? If so return 0, otherwise return

 * error.

 */

static unsigned long check_mremap_params(struct vma_remap_struct *vrm)



{

	struct mm_struct *mm = current->mm;

	unsigned long addr = vrm->addr;

	unsigned long flags = vrm->flags;



	/* Regardless of success/failure, we always notify of any unmaps. */

	userfaultfd_unmap_complete(mm, vrm->uf_unmap_early);

	if (failed)

		mremap_userfaultfd_fail(vrm->uf);

	else

		mremap_userfaultfd_complete(vrm->uf, vrm->addr,

			vrm->new_addr, vrm->old_len);

	userfaultfd_unmap_complete(mm, vrm->uf_unmap);

	/* Ensure no unexpected flag values. */

	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))

		return -EINVAL;



	/* Start address must be page-aligned. */

	if (offset_in_page(addr))

		return -EINVAL;



	/*

	 * We allow a zero old-len as a special case

	 * for DOS-emu "duplicate shm area" thing. But

	 * a zero new-len is nonsensical.

	 */

	if (!vrm->new_len)

		return -EINVAL;



	/* Is the new length or address silly? */

	if (vrm->new_len > TASK_SIZE ||

	    vrm->new_addr > TASK_SIZE - vrm->new_len)

		return -EINVAL;



	/* Remainder of checks are for cases with specific new_addr. */

	if (!vrm_implies_new_addr(vrm))

		return 0;



	/* The new address must be page-aligned. */

	if (offset_in_page(vrm->new_addr))

		return -EINVAL;



	/* A fixed address implies a move. */

	if (!(flags & MREMAP_MAYMOVE))

		return -EINVAL;



	/* MREMAP_DONTUNMAP does not allow resizing in the process. */

	if (flags & MREMAP_DONTUNMAP && vrm->old_len != vrm->new_len)

		return -EINVAL;



	/* Target VMA must not overlap source VMA. */

	if (vrm_overlaps(vrm))

		return -EINVAL;



	/*

	 * move_vma() need us to stay 4 maps below the threshold, otherwise

	 * it will bail out at the very beginning.

	 * That is a problem if we have already unmaped the regions here

	 * (new_addr, and old_addr), because userspace will not know the

	 * state of the vma's after it gets -ENOMEM.

	 * So, to avoid such scenario we can pre-compute if the whole

	 * operation has high chances to success map-wise.

	 * Worst-scenario case is when both vma's (new_addr and old_addr) get

	 * split in 3 before unmapping it.

	 * That means 2 more maps (1 for each) to the ones we already hold.

	 * Check whether current map count plus 2 still leads us to 4 maps below

	 * the threshold, otherwise return -ENOMEM here to be more safe.

	 */

	if ((current->mm->map_count + 2) >= sysctl_max_map_count - 3)

		return -ENOMEM;



	return 0;

}



static unsigned long do_mremap(struct vma_remap_struct *vrm)