lkml.org 
[lkml]   [2012]   [Mar]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 2/2] hugepages: Fix use after free bug in "quota" handling
From
On Wed, Mar 7, 2012 at 12:48 PM, David Gibson
<david@gibson.dropbear.id.au> wrote:
> hugetlbfs_{get,put}_quota() are badly named.  They don't interact with the
> general quota handling code, and they don't much resemble its behaviour.
> Rather than being about maintaining limits on on-disk block usage by
> particular users, they are instead about maintaining limits on in-memory
> page usage (including anonymous MAP_PRIVATE copied-on-write pages)
> associated with a particular hugetlbfs filesystem instance.
>
> Worse, they work by having callbacks to the hugetlbfs filesystem code from
> the low-level page handling code, in particular from free_huge_page().
> This is a layering violation of itself, but more importantly, if the kernel
> does a get_user_pages() on hugepages (which can happen from KVM amongst
> others), then the free_huge_page() can be delayed until after the
> associated inode has already been freed.  If an unmount occurs at the
> wrong time, even the hugetlbfs superblock where the "quota" limits are
> stored may have been freed.
>
> Andrew Barry proposed a patch to fix this by having hugepages, instead of
> storing a pointer to their address_space and reaching the superblock from
> there, had the hugepages store pointers directly to the superblock, bumping
> the reference count as appropriate to avoid it being freed.  Andrew Morton
> rejected that version, however, on the grounds that it made the existing
> layering violation worse.
>
> This is a reworked version of Andrew's patch, which removes the extra, and
> some of the existing, layering violation.  It works by introducing the
> concept of a hugepage "subpool" at the lower hugepage mm layer - that is
> a finite logical pool of hugepages to allocate from.  hugetlbfs now creates
> a subpool for each filesystem instance with a page limit set, and a pointer
> to the subpool gets added to each allocated hugepage, instead of the
> address_space pointer used now.  The subpool has its own lifetime and is
> only freed once all pages in it _and_ all other references to it (i.e.
> superblocks) are gone.
>
> subpools are optional - a NULL subpool pointer is taken by the code to mean
> that no subpool limits are in effect.
>
> Previous discussion of this bug found in:  "Fix refcounting in hugetlbfs
> quota handling.". See:  https://lkml.org/lkml/2011/8/11/28 or
> http://marc.info/?l=linux-mm&m=126928970510627&w=1
>
> v2: Fixed a bug spotted by Hillf Danton, and removed the extra parameter to
> alloc_huge_page() - since it already takes the vma, it is not necessary.
>
> Signed-off-by: Andrew Barry <abarry@cray.com>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Minchan Kim <minchan.kim@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Hillf Danton <dhillf@gmail.com>
> ---
>  fs/hugetlbfs/inode.c    |   54 +++++++-----------
>  include/linux/hugetlb.h |   14 ++++--
>  mm/hugetlb.c            |  135 +++++++++++++++++++++++++++++++++++++---------
>  3 files changed, 139 insertions(+), 64 deletions(-)
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index bb0e366..74c6ba2 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -626,9 +626,15 @@ static int hugetlbfs_statfs(struct dentry *dentry, struct kstatfs *buf)
>                spin_lock(&sbinfo->stat_lock);
>                /* If no limits set, just report 0 for max/free/used
>                 * blocks, like simple_statfs() */
> -               if (sbinfo->max_blocks >= 0) {
> -                       buf->f_blocks = sbinfo->max_blocks;
> -                       buf->f_bavail = buf->f_bfree = sbinfo->free_blocks;
> +               if (sbinfo->spool) {
> +                       long free_pages;
> +
> +                       spin_lock(&sbinfo->spool->lock);
> +                       buf->f_blocks = sbinfo->spool->max_hpages;
> +                       free_pages = sbinfo->spool->max_hpages
> +                               - sbinfo->spool->used_hpages;
> +                       buf->f_bavail = buf->f_bfree = free_pages;
> +                       spin_unlock(&sbinfo->spool->lock);
>                        buf->f_files = sbinfo->max_inodes;
>                        buf->f_ffree = sbinfo->free_inodes;
>                }
> @@ -644,6 +650,10 @@ static void hugetlbfs_put_super(struct super_block *sb)
>
>        if (sbi) {
>                sb->s_fs_info = NULL;
> +
> +               if (sbi->spool)
> +                       hugepage_put_subpool(sbi->spool);
> +
>                kfree(sbi);
>        }
>  }
> @@ -874,10 +884,14 @@ hugetlbfs_fill_super(struct super_block *sb, void *data, int silent)
>        sb->s_fs_info = sbinfo;
>        sbinfo->hstate = config.hstate;
>        spin_lock_init(&sbinfo->stat_lock);
> -       sbinfo->max_blocks = config.nr_blocks;
> -       sbinfo->free_blocks = config.nr_blocks;
>        sbinfo->max_inodes = config.nr_inodes;
>        sbinfo->free_inodes = config.nr_inodes;
> +       sbinfo->spool = NULL;
> +       if (config.nr_blocks != -1) {
> +               sbinfo->spool = hugepage_new_subpool(config.nr_blocks);
> +               if (!sbinfo->spool)
> +                       goto out_free;
> +       }
>        sb->s_maxbytes = MAX_LFS_FILESIZE;
>        sb->s_blocksize = huge_page_size(config.hstate);
>        sb->s_blocksize_bits = huge_page_shift(config.hstate);
> @@ -896,38 +910,12 @@ hugetlbfs_fill_super(struct super_block *sb, void *data, int silent)
>        sb->s_root = root;
>        return 0;
>  out_free:
> +       if (sbinfo->spool)
> +               kfree(sbinfo->spool);
>        kfree(sbinfo);
>        return -ENOMEM;
>  }
>
> -int hugetlb_get_quota(struct address_space *mapping, long delta)
> -{
> -       int ret = 0;
> -       struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(mapping->host->i_sb);
> -
> -       if (sbinfo->free_blocks > -1) {
> -               spin_lock(&sbinfo->stat_lock);
> -               if (sbinfo->free_blocks - delta >= 0)
> -                       sbinfo->free_blocks -= delta;
> -               else
> -                       ret = -ENOMEM;
> -               spin_unlock(&sbinfo->stat_lock);
> -       }
> -
> -       return ret;
> -}
> -
> -void hugetlb_put_quota(struct address_space *mapping, long delta)
> -{
> -       struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(mapping->host->i_sb);
> -
> -       if (sbinfo->free_blocks > -1) {
> -               spin_lock(&sbinfo->stat_lock);
> -               sbinfo->free_blocks += delta;
> -               spin_unlock(&sbinfo->stat_lock);
> -       }
> -}
> -
>  static struct dentry *hugetlbfs_mount(struct file_system_type *fs_type,
>        int flags, const char *dev_name, void *data)
>  {
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 7adc492..cf01817 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -14,6 +14,15 @@ struct user_struct;
>  #include <linux/shm.h>
>  #include <asm/tlbflush.h>
>
> +struct hugepage_subpool {
> +       spinlock_t lock;
> +       long count;
> +       long max_hpages, used_hpages;
> +};
> +
> +struct hugepage_subpool *hugepage_new_subpool(long nr_blocks);
> +void hugepage_put_subpool(struct hugepage_subpool *spool);
> +
>  int PageHuge(struct page *page);
>
>  void reset_vma_resv_huge_pages(struct vm_area_struct *vma);
> @@ -129,12 +138,11 @@ enum {
>
>  #ifdef CONFIG_HUGETLBFS
>  struct hugetlbfs_sb_info {
> -       long    max_blocks;   /* blocks allowed */
> -       long    free_blocks;  /* blocks free */
>        long    max_inodes;   /* inodes allowed */
>        long    free_inodes;  /* inodes free */
>        spinlock_t      stat_lock;
>        struct hstate *hstate;
> +       struct hugepage_subpool *spool;
>  };
>
>  static inline struct hugetlbfs_sb_info *HUGETLBFS_SB(struct super_block *sb)
> @@ -146,8 +154,6 @@ extern const struct file_operations hugetlbfs_file_operations;
>  extern const struct vm_operations_struct hugetlb_vm_ops;
>  struct file *hugetlb_file_setup(const char *name, size_t size, vm_flags_t acct,
>                                struct user_struct **user, int creat_flags);
> -int hugetlb_get_quota(struct address_space *mapping, long delta);
> -void hugetlb_put_quota(struct address_space *mapping, long delta);
>
>  static inline int is_file_hugepages(struct file *file)
>  {
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 5f34bd8..36b38b3a 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -53,6 +53,84 @@ static unsigned long __initdata default_hstate_size;
>  */
>  static DEFINE_SPINLOCK(hugetlb_lock);
>
> +static inline void unlock_or_release_subpool(struct hugepage_subpool *spool)
> +{
> +       bool free = (spool->count == 0) && (spool->used_hpages == 0);
> +
> +       spin_unlock(&spool->lock);
> +
> +       /* If no pages are used, and no other handles to the subpool
> +        * remain, free the subpool the subpool remain */
> +       if (free)
> +               kfree(spool);
> +}
> +
> +struct hugepage_subpool *hugepage_new_subpool(long nr_blocks)
> +{
> +       struct hugepage_subpool *spool;
> +
> +       spool = kmalloc(sizeof(*spool), GFP_KERNEL);
> +       if (!spool)
> +               return NULL;
> +
> +       spin_lock_init(&spool->lock);
> +       spool->count = 1;
> +       spool->max_hpages = nr_blocks;
> +       spool->used_hpages = 0;
> +
> +       return spool;
> +}
> +
> +void hugepage_put_subpool(struct hugepage_subpool *spool)
> +{
> +       spin_lock(&spool->lock);
> +       BUG_ON(!spool->count);
> +       spool->count--;
> +       unlock_or_release_subpool(spool);
> +}
> +
> +static int hugepage_subpool_get_pages(struct hugepage_subpool *spool,
> +                                     long delta)
> +{
> +       int ret = 0;
> +
> +       if (!spool)
> +               return 0;
> +
> +       spin_lock(&spool->lock);
> +       if ((spool->used_hpages + delta) <= spool->max_hpages) {
> +               spool->used_hpages += delta;
> +       } else {
> +               ret = -ENOMEM;
> +       }
> +       spin_unlock(&spool->lock);
> +
> +       return ret;
> +}
> +
> +static void hugepage_subpool_put_pages(struct hugepage_subpool *spool,
> +                                      long delta)
> +{
> +       if (!spool)
> +               return;
> +
> +       spin_lock(&spool->lock);
> +       spool->used_hpages -= delta;
> +       /* If hugetlbfs_put_super couldn't free spool due to
> +       * an outstanding quota reference, free it now. */
> +       unlock_or_release_subpool(spool);
> +}
> +
> +static inline struct hugepage_subpool *subpool_inode(struct inode *inode)
> +{
> +       return HUGETLBFS_SB(inode->i_sb)->spool;
> +}
> +
> +static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
> +{
> +       return subpool_inode(vma->vm_file->f_dentry->d_inode);
> +}
> +
>  /*
>  * Region tracking -- allows tracking of reservations and instantiated pages
>  *                    across the pages in a mapping.
> @@ -533,9 +611,9 @@ static void free_huge_page(struct page *page)
>         */
>        struct hstate *h = page_hstate(page);
>        int nid = page_to_nid(page);
> -       struct address_space *mapping;
> +       struct hugepage_subpool *spool =
> +               (struct hugepage_subpool *)page_private(page);
>
> -       mapping = (struct address_space *) page_private(page);
>        set_page_private(page, 0);
>        page->mapping = NULL;
>        BUG_ON(page_count(page));
> @@ -551,8 +629,7 @@ static void free_huge_page(struct page *page)
>                enqueue_huge_page(h, page);
>        }
>        spin_unlock(&hugetlb_lock);
> -       if (mapping)
> -               hugetlb_put_quota(mapping, 1);
> +       hugepage_subpool_put_pages(spool, 1);

Like current code, quota is handed back *unconditionally*, but ...

>  }
>
>  static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
> @@ -966,11 +1043,12 @@ static void return_unused_surplus_pages(struct hstate *h,
>  /*
>  * Determine if the huge page at addr within the vma has an associated
>  * reservation.  Where it does not we will need to logically increase
> - * reservation and actually increase quota before an allocation can occur.
> - * Where any new reservation would be required the reservation change is
> - * prepared, but not committed.  Once the page has been quota'd allocated
> - * an instantiated the change should be committed via vma_commit_reservation.
> - * No action is required on failure.
> + * reservation and actually increase subpool usage before an allocation
> + * can occur.  Where any new reservation would be required the
> + * reservation change is prepared, but not committed.  Once the page
> + * has been allocated from the subpool and instantiated the change should
> + * be committed via vma_commit_reservation.  No action is required on
> + * failure.
>  */
>  static long vma_needs_reservation(struct hstate *h,
>                        struct vm_area_struct *vma, unsigned long addr)
> @@ -1019,24 +1097,24 @@ static void vma_commit_reservation(struct hstate *h,
>  static struct page *alloc_huge_page(struct vm_area_struct *vma,
>                                    unsigned long addr, int avoid_reserve)
>  {
> +       struct hugepage_subpool *spool = subpool_vma(vma);
>        struct hstate *h = hstate_vma(vma);
>        struct page *page;
> -       struct address_space *mapping = vma->vm_file->f_mapping;
> -       struct inode *inode = mapping->host;
>        long chg;
>
>        /*
> -        * Processes that did not create the mapping will have no reserves and
> -        * will not have accounted against quota. Check that the quota can be
> -        * made before satisfying the allocation
> -        * MAP_NORESERVE mappings may also need pages and quota allocated
> -        * if no reserve mapping overlaps.
> +        * Processes that did not create the mapping will have no
> +        * reserves and will not have accounted against subpool
> +        * limit. Check that the subpool limit can be made before
> +        * satisfying the allocation MAP_NORESERVE mappings may also
> +        * need pages and subpool limit allocated allocated if no reserve
> +        * mapping overlaps.
>         */
>        chg = vma_needs_reservation(h, vma, addr);
>        if (chg < 0)
>                return ERR_PTR(-VM_FAULT_OOM);
>        if (chg)
> -               if (hugetlb_get_quota(inode->i_mapping, chg))
> +               if (hugepage_subpool_get_pages(spool, chg))
>                        return ERR_PTR(-VM_FAULT_SIGBUS);

... quota is allocated only if needed.

Given that mismatch, are you fixing the use-after-free bug, or
quota maintenance, or both?

>
>        spin_lock(&hugetlb_lock);
> @@ -1046,12 +1124,12 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>        if (!page) {
>                page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
>                if (!page) {
> -                       hugetlb_put_quota(inode->i_mapping, chg);
> +                       hugepage_subpool_put_pages(spool, chg);
>                        return ERR_PTR(-VM_FAULT_SIGBUS);
>                }
>        }
>
> -       set_page_private(page, (unsigned long) mapping);
> +       set_page_private(page, (unsigned long)spool);
>
>        vma_commit_reservation(h, vma, addr);
>
> @@ -2072,6 +2150,7 @@ static void hugetlb_vm_op_close(struct vm_area_struct *vma)
>  {
>        struct hstate *h = hstate_vma(vma);
>        struct resv_map *reservations = vma_resv_map(vma);
> +       struct hugepage_subpool *spool = subpool_vma(vma);
>        unsigned long reserve;
>        unsigned long start;
>        unsigned long end;
> @@ -2087,7 +2166,7 @@ static void hugetlb_vm_op_close(struct vm_area_struct *vma)
>
>                if (reserve) {
>                        hugetlb_acct_memory(h, -reserve);
> -                       hugetlb_put_quota(vma->vm_file->f_mapping, reserve);
> +                       hugepage_subpool_put_pages(spool, reserve);
>                }
>        }
>  }
> @@ -2316,7 +2395,7 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
>         */
>        address = address & huge_page_mask(h);
>        pgoff = vma_hugecache_offset(h, vma, address);
> -       mapping = (struct address_space *)page_private(page);
> +       mapping = vma->vm_file->f_dentry->d_inode->i_mapping;
>
>        /*
>         * Take the mapping lock for the duration of the table walk. As
> @@ -2869,11 +2948,12 @@ int hugetlb_reserve_pages(struct inode *inode,
>  {
>        long ret, chg;
>        struct hstate *h = hstate_inode(inode);
> +       struct hugepage_subpool *spool = subpool_inode(inode);
>
>        /*
>         * Only apply hugepage reservation if asked. At fault time, an
>         * attempt will be made for VM_NORESERVE to allocate a page
> -        * and filesystem quota without using reserves
> +        * without using reserves
>         */
>        if (vm_flags & VM_NORESERVE)
>                return 0;
> @@ -2900,17 +2980,17 @@ int hugetlb_reserve_pages(struct inode *inode,
>        if (chg < 0)
>                return chg;
>
> -       /* There must be enough filesystem quota for the mapping */
> -       if (hugetlb_get_quota(inode->i_mapping, chg))
> +       /* There must be enough pages in the subpool for the mapping */
> +       if (hugepage_subpool_get_pages(spool, chg))
>                return -ENOSPC;
>
>        /*
>         * Check enough hugepages are available for the reservation.
> -        * Hand back the quota if there are not
> +        * Hand the pages back to the subpool if there are not
>         */
>        ret = hugetlb_acct_memory(h, chg);
>        if (ret < 0) {
> -               hugetlb_put_quota(inode->i_mapping, chg);
> +               hugepage_subpool_put_pages(spool, chg);
>                return ret;
>        }
>
> @@ -2934,12 +3014,13 @@ void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed)
>  {
>        struct hstate *h = hstate_inode(inode);
>        long chg = region_truncate(&inode->i_mapping->private_list, offset);
> +       struct hugepage_subpool *spool = subpool_inode(inode);
>
>        spin_lock(&inode->i_lock);
>        inode->i_blocks -= (blocks_per_huge_page(h) * freed);
>        spin_unlock(&inode->i_lock);
>
> -       hugetlb_put_quota(inode->i_mapping, (chg - freed));
> +       hugepage_subpool_put_pages(spool, (chg - freed));
>        hugetlb_acct_memory(h, -(chg - freed));
>  }
>
> --
> 1.7.9.1
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2012-03-07 13:31    [from the cache]
©2003-2011 Jasper Spaans