Messages in this thread | | | Date | Wed, 7 Mar 2012 20:28:39 +0800 | Subject | Re: [PATCH 2/2] hugepages: Fix use after free bug in "quota" handling | From | Hillf Danton <> |
| |
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/
| |