This patch fixes a use-after-free problem in free_huge_page, with a quota update happening after hugetlbfs umount. The problem results when a device driver, which has mapped a hugepage, does a put_page. Put_page, calls free_huge_page, which does a hugetlb_put_quota. As written, hugetlb_put_quota takes an address_space struct pointer "mapping" as an argument. If the put_page occurs after the hugetlbfs filesystem is unmounted, mapping points to freed memory. Hugetlb_put_quota doesn't need the address_space pointer, it only uses it to find the quota-record. Rather than an address-space struct pointer, this patched code puts a hugetlbfs_sb_info struct pointer into page_private of the page struct. In order to prevent the quota record from being freed at unmount, a reference count and an active bit are added to the hugetlbfs_sb_info struct; the reference count is increased by hugetlb_get_quota and decreased by hugetlb_put_quota. When hugetlbfs is unmounted, it frees the hugetlbfs_sb_info struct, but only if the reference count is zero. If the reference count is not zero, it clears the active bit, and the last hugetlb_put_quota then frees the hugetlbfs_sb_info struct. Discussion was titled: Fix refcounting in hugetlbfs quota handling. See: https://lkml.org/lkml/2011/8/11/28 See also: http://marc.info/?l=linux-mm&m=126928970510627&w=1 Version 2: Adding better description of how the race happens, removing unnecessary inode->i_mapping->host->i_sb indirection when inode->i_sb has the same meaning. Signed-off-by: Andrew Barry <abarry@xxxxxxxx> Cc: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Minchan Kim <minchan.kim@xxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/hugetlbfs/inode.c | 40 ++++++++++++++++++++++++++-------------- include/linux/hugetlb.h | 9 +++++++-- mm/hugetlb.c | 23 ++++++++++++----------- 3 files changed, 45 insertions(+), 27 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 87b6e04..2ed1cca 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -615,8 +615,12 @@ static void hugetlbfs_put_super(struct s struct hugetlbfs_sb_info *sbi = HUGETLBFS_SB(sb); if (sbi) { + sbi->active = HPAGE_INACTIVE; sb->s_fs_info = NULL; - kfree(sbi); + + /*Free only if used quota is zero. */ + if (sbi->used_blocks == 0) + kfree(sbi); } } @@ -851,6 +855,8 @@ hugetlbfs_fill_super(struct super_block sbinfo->free_blocks = config.nr_blocks; sbinfo->max_inodes = config.nr_inodes; sbinfo->free_inodes = config.nr_inodes; + sbinfo->used_blocks = 0; + sbinfo->active = HPAGE_ACTIVE; sb->s_maxbytes = MAX_LFS_FILESIZE; sb->s_blocksize = huge_page_size(config.hstate); sb->s_blocksize_bits = huge_page_shift(config.hstate); @@ -874,30 +880,36 @@ out_free: return -ENOMEM; } -int hugetlb_get_quota(struct address_space *mapping, long delta) +int hugetlb_get_quota(struct hugetlbfs_sb_info *sbinfo, 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) + spin_lock(&sbinfo->stat_lock); + if ((sbinfo->free_blocks == -1) || (sbinfo->free_blocks - delta >= 0)) { + if (sbinfo->free_blocks != -1) sbinfo->free_blocks -= delta; - else - ret = -ENOMEM; - spin_unlock(&sbinfo->stat_lock); + sbinfo->used_blocks += delta; + sbinfo->active = HPAGE_ACTIVE; + } else { + ret = -ENOMEM; } + spin_unlock(&sbinfo->stat_lock); return ret; } -void hugetlb_put_quota(struct address_space *mapping, long delta) +void hugetlb_put_quota(struct hugetlbfs_sb_info *sbinfo, long delta) { - struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(mapping->host->i_sb); - - if (sbinfo->free_blocks > -1) { - spin_lock(&sbinfo->stat_lock); + spin_lock(&sbinfo->stat_lock); + if (sbinfo->free_blocks > -1) sbinfo->free_blocks += delta; + sbinfo->used_blocks -= delta; + /* If hugetlbfs_put_super couldn't free sbinfo due to + * an outstanding quota reference, free it now. */ + if ((sbinfo->used_blocks == 0) && (sbinfo->active == HPAGE_INACTIVE)) { + spin_unlock(&sbinfo->stat_lock); + kfree(sbinfo); + } else { spin_unlock(&sbinfo->stat_lock); } } diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 19644e0..8780a91 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -142,11 +142,16 @@ struct hugetlbfs_config { struct hstate *hstate; }; +#define HPAGE_INACTIVE 0 +#define HPAGE_ACTIVE 1 + struct hugetlbfs_sb_info { long max_blocks; /* blocks allowed */ long free_blocks; /* blocks free */ long max_inodes; /* inodes allowed */ long free_inodes; /* inodes free */ + long used_blocks; /* blocks used */ + long active; /* active bit */ spinlock_t stat_lock; struct hstate *hstate; }; @@ -171,8 +176,8 @@ extern const struct file_operations huge 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); +int hugetlb_get_quota(struct hugetlbfs_sb_info *sbinfo, long delta); +void hugetlb_put_quota(struct hugetlbfs_sb_info *sbinfo, long delta); static inline int is_file_hugepages(struct file *file) { diff --git a/mm/hugetlb.c b/mm/hugetlb.c index dae27ba..0f39cde 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -533,9 +533,9 @@ static void free_huge_page(struct page * */ struct hstate *h = page_hstate(page); int nid = page_to_nid(page); - struct address_space *mapping; + struct hugetlbfs_sb_info *sbinfo; - mapping = (struct address_space *) page_private(page); + sbinfo = ( struct hugetlbfs_sb_info *) page_private(page); set_page_private(page, 0); page->mapping = NULL; BUG_ON(page_count(page)); @@ -551,8 +551,8 @@ static void free_huge_page(struct page * enqueue_huge_page(h, page); } spin_unlock(&hugetlb_lock); - if (mapping) - hugetlb_put_quota(mapping, 1); + if (sbinfo) + hugetlb_put_quota(sbinfo, 1); } static void prep_new_huge_page(struct hstate *h, struct page *page, int nid) @@ -1035,7 +1035,7 @@ static struct page *alloc_huge_page(stru if (chg < 0) return ERR_PTR(-VM_FAULT_OOM); if (chg) - if (hugetlb_get_quota(inode->i_mapping, chg)) + if (hugetlb_get_quota(HUGETLBFS_SB(inode->i_sb), chg)) return ERR_PTR(-VM_FAULT_SIGBUS); spin_lock(&hugetlb_lock); @@ -1045,12 +1045,12 @@ static struct page *alloc_huge_page(stru if (!page) { page = alloc_buddy_huge_page(h, NUMA_NO_NODE); if (!page) { - hugetlb_put_quota(inode->i_mapping, chg); + hugetlb_put_quota(HUGETLBFS_SB(inode->i_sb), chg); return ERR_PTR(-VM_FAULT_SIGBUS); } } - set_page_private(page, (unsigned long) mapping); + set_page_private(page, (unsigned long) HUGETLBFS_SB(inode->i_sb)); vma_commit_reservation(h, vma, addr); @@ -2086,7 +2086,8 @@ static void hugetlb_vm_op_close(struct v if (reserve) { hugetlb_acct_memory(h, -reserve); - hugetlb_put_quota(vma->vm_file->f_mapping, reserve); + hugetlb_put_quota(HUGETLBFS_SB( + vma->vm_file->f_mapping->host->i_sb), reserve); } } } @@ -2884,7 +2885,7 @@ int hugetlb_reserve_pages(struct inode * return chg; /* There must be enough filesystem quota for the mapping */ - if (hugetlb_get_quota(inode->i_mapping, chg)) + if (hugetlb_get_quota(HUGETLBFS_SB(inode->i_sb), chg)) return -ENOSPC; /* @@ -2893,7 +2894,7 @@ int hugetlb_reserve_pages(struct inode * */ ret = hugetlb_acct_memory(h, chg); if (ret < 0) { - hugetlb_put_quota(inode->i_mapping, chg); + hugetlb_put_quota(HUGETLBFS_SB(inode->i_sb), chg); return ret; } @@ -2922,7 +2923,7 @@ void hugetlb_unreserve_pages(struct inod inode->i_blocks -= (blocks_per_huge_page(h) * freed); spin_unlock(&inode->i_lock); - hugetlb_put_quota(inode->i_mapping, (chg - freed)); + hugetlb_put_quota(HUGETLBFS_SB(inode->i_sb), (chg - freed)); hugetlb_acct_memory(h, -(chg - freed)); } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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