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    Subject[PATCH 5.0 10/46] staging: erofs: fix race of initializing xattrs of a inode at the same time
    Date
    5.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Gao Xiang <gaoxiang25@huawei.com>

    commit 62dc45979f3f8cb0ea67302a93bff686f0c46c5a upstream.

    In real scenario, there could be several threads accessing xattrs
    of the same xattr-uninitialized inode, and init_inode_xattrs()
    almost at the same time.

    That's actually an unexpected behavior, this patch closes the race.

    Fixes: b17500a0fdba ("staging: erofs: introduce xattr & acl support")
    Cc: <stable@vger.kernel.org> # 4.19+
    Reviewed-by: Chao Yu <yuchao0@huawei.com>
    Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/staging/erofs/internal.h | 11 +++++++---
    drivers/staging/erofs/xattr.c | 41 +++++++++++++++++++++++++++------------
    2 files changed, 37 insertions(+), 15 deletions(-)

    --- a/drivers/staging/erofs/internal.h
    +++ b/drivers/staging/erofs/internal.h
    @@ -354,12 +354,17 @@ static inline erofs_off_t iloc(struct er
    return blknr_to_addr(sbi->meta_blkaddr) + (nid << sbi->islotbits);
    }

    -#define inode_set_inited_xattr(inode) (EROFS_V(inode)->flags |= 1)
    -#define inode_has_inited_xattr(inode) (EROFS_V(inode)->flags & 1)
    +/* atomic flag definitions */
    +#define EROFS_V_EA_INITED_BIT 0
    +
    +/* bitlock definitions (arranged in reverse order) */
    +#define EROFS_V_BL_XATTR_BIT (BITS_PER_LONG - 1)

    struct erofs_vnode {
    erofs_nid_t nid;
    - unsigned int flags;
    +
    + /* atomic flags (including bitlocks) */
    + unsigned long flags;

    unsigned char data_mapping_mode;
    /* inline size in bytes */
    --- a/drivers/staging/erofs/xattr.c
    +++ b/drivers/staging/erofs/xattr.c
    @@ -44,18 +44,25 @@ static inline void xattr_iter_end_final(

    static int init_inode_xattrs(struct inode *inode)
    {
    + struct erofs_vnode *const vi = EROFS_V(inode);
    struct xattr_iter it;
    unsigned int i;
    struct erofs_xattr_ibody_header *ih;
    struct super_block *sb;
    struct erofs_sb_info *sbi;
    - struct erofs_vnode *vi;
    bool atomic_map;
    + int ret = 0;

    - if (likely(inode_has_inited_xattr(inode)))
    + /* the most case is that xattrs of this inode are initialized. */
    + if (test_bit(EROFS_V_EA_INITED_BIT, &vi->flags))
    return 0;

    - vi = EROFS_V(inode);
    + if (wait_on_bit_lock(&vi->flags, EROFS_V_BL_XATTR_BIT, TASK_KILLABLE))
    + return -ERESTARTSYS;
    +
    + /* someone has initialized xattrs for us? */
    + if (test_bit(EROFS_V_EA_INITED_BIT, &vi->flags))
    + goto out_unlock;

    /*
    * bypass all xattr operations if ->xattr_isize is not greater than
    @@ -68,13 +75,16 @@ static int init_inode_xattrs(struct inod
    if (vi->xattr_isize == sizeof(struct erofs_xattr_ibody_header)) {
    errln("xattr_isize %d of nid %llu is not supported yet",
    vi->xattr_isize, vi->nid);
    - return -ENOTSUPP;
    + ret = -ENOTSUPP;
    + goto out_unlock;
    } else if (vi->xattr_isize < sizeof(struct erofs_xattr_ibody_header)) {
    if (unlikely(vi->xattr_isize)) {
    DBG_BUGON(1);
    - return -EIO; /* xattr ondisk layout error */
    + ret = -EIO;
    + goto out_unlock; /* xattr ondisk layout error */
    }
    - return -ENOATTR;
    + ret = -ENOATTR;
    + goto out_unlock;
    }

    sb = inode->i_sb;
    @@ -83,8 +93,10 @@ static int init_inode_xattrs(struct inod
    it.ofs = erofs_blkoff(iloc(sbi, vi->nid) + vi->inode_isize);

    it.page = erofs_get_inline_page(inode, it.blkaddr);
    - if (IS_ERR(it.page))
    - return PTR_ERR(it.page);
    + if (IS_ERR(it.page)) {
    + ret = PTR_ERR(it.page);
    + goto out_unlock;
    + }

    /* read in shared xattr array (non-atomic, see kmalloc below) */
    it.kaddr = kmap(it.page);
    @@ -97,7 +109,8 @@ static int init_inode_xattrs(struct inod
    sizeof(uint), GFP_KERNEL);
    if (vi->xattr_shared_xattrs == NULL) {
    xattr_iter_end(&it, atomic_map);
    - return -ENOMEM;
    + ret = -ENOMEM;
    + goto out_unlock;
    }

    /* let's skip ibody header */
    @@ -114,7 +127,8 @@ static int init_inode_xattrs(struct inod
    if (IS_ERR(it.page)) {
    kfree(vi->xattr_shared_xattrs);
    vi->xattr_shared_xattrs = NULL;
    - return PTR_ERR(it.page);
    + ret = PTR_ERR(it.page);
    + goto out_unlock;
    }

    it.kaddr = kmap_atomic(it.page);
    @@ -127,8 +141,11 @@ static int init_inode_xattrs(struct inod
    }
    xattr_iter_end(&it, atomic_map);

    - inode_set_inited_xattr(inode);
    - return 0;
    + set_bit(EROFS_V_EA_INITED_BIT, &vi->flags);
    +
    +out_unlock:
    + clear_and_wake_up_bit(EROFS_V_BL_XATTR_BIT, &vi->flags);
    + return ret;
    }

    /*

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