Messages in this thread | | | From | "Aneesh Kumar K.V" <> | Subject | Re: [PATCH 2/2] hugepages: Fix use after free bug in "quota" handling | Date | Thu, 08 Mar 2012 09:47:05 +0530 |
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On Wed, 7 Mar 2012 20:28:39 +0800, Hillf Danton <dhillf@gmail.com> wrote: > 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 ...
We will end up doing get_quota for every allocated page. get_quota happens either during mmap() if MAP_NORESERVE is not specified. or during alloc_huge_page if we haven't done a quota reservation during mmap for that range. Are you finding any part of code where we miss that ?
-aneesh
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