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    Subject[PATCH 1/2] mm: set S_SWAPFILE on blockdev swap devices
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    From: Darrick J. Wong <darrick.wong@oracle.com>

    Set S_SWAPFILE on block device inodes so that they have the same
    protections as a swap flie.

    Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
    ---
    mm/swapfile.c | 31 +++++++++++++++----------------
    1 file changed, 15 insertions(+), 16 deletions(-)


    diff --git a/mm/swapfile.c b/mm/swapfile.c
    index 0789a762ce2f..a53b7c49b40e 100644
    --- a/mm/swapfile.c
    +++ b/mm/swapfile.c
    @@ -2368,9 +2368,8 @@ EXPORT_SYMBOL_GPL(add_swap_extent);
    * requirements, they are simply tossed out - we will never use those blocks
    * for swapping.
    *
    - * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon. This
    - * prevents root from shooting her foot off by ftruncating an in-use swapfile,
    - * which will scribble on the fs.
    + * For all swap devices we set S_SWAPFILE across the life of the swapon. This
    + * prevents users from writing to the swap device, which will corrupt memory.
    *
    * The amount of disk space which a single swap extent represents varies.
    * Typically it is in the 1-4 megabyte range. So we can have hundreds of
    @@ -2661,13 +2660,14 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
    inode = mapping->host;
    if (S_ISBLK(inode->i_mode)) {
    struct block_device *bdev = I_BDEV(inode);
    +
    set_blocksize(bdev, old_block_size);
    blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
    - } else {
    - inode_lock(inode);
    - inode->i_flags &= ~S_SWAPFILE;
    - inode_unlock(inode);
    }
    +
    + inode_lock(inode);
    + inode->i_flags &= ~S_SWAPFILE;
    + inode_unlock(inode);
    filp_close(swap_file, NULL);

    /*
    @@ -2890,11 +2890,11 @@ static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
    p->flags |= SWP_BLKDEV;
    } else if (S_ISREG(inode->i_mode)) {
    p->bdev = inode->i_sb->s_bdev;
    - inode_lock(inode);
    - if (IS_SWAPFILE(inode))
    - return -EBUSY;
    - } else
    - return -EINVAL;
    + }
    +
    + inode_lock(inode);
    + if (IS_SWAPFILE(inode))
    + return -EBUSY;

    return 0;
    }
    @@ -3295,8 +3295,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
    atomic_inc(&proc_poll_event);
    wake_up_interruptible(&proc_poll_wait);

    - if (S_ISREG(inode->i_mode))
    - inode->i_flags |= S_SWAPFILE;
    + inode->i_flags |= S_SWAPFILE;
    error = 0;
    goto out;
    bad_swap:
    @@ -3318,7 +3317,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
    if (inced_nr_rotate_swap)
    atomic_dec(&nr_rotate_swap);
    if (swap_file) {
    - if (inode && S_ISREG(inode->i_mode)) {
    + if (inode) {
    inode_unlock(inode);
    inode = NULL;
    }
    @@ -3331,7 +3330,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
    }
    if (name)
    putname(name);
    - if (inode && S_ISREG(inode->i_mode))
    + if (inode)
    inode_unlock(inode);
    if (!error)
    enable_swap_slots_cache();
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