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vfs: don't allow writes to swap files

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Don't let userspace write to an active swap file because the kernel
effectively has a long term lease on the storage and things could get
seriously corrupted if we let this happen.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Darrick J. Wong 2019-08-20 07:55:16 -07:00 committed by Jaegeuk Kim
parent a9f3d1d15b
commit 8cfd90e159
6 changed files with 38 additions and 3 deletions
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3
fs/block_dev.c
View file

@ -1901,6 +1901,9 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
if (bdev_read_only(I_BDEV(bd_inode)))
return -EPERM;
if (IS_SWAPFILE(bd_inode))
return -ETXTBSY;
if (!iov_iter_count(from))
return 0;

11
include/linux/fs.h
View file

@ -3479,4 +3479,15 @@ static inline void simple_fill_fsxattr(struct fsxattr *fa, __u32 xflags)
fa->fsx_xflags = xflags;
}
/*
* Flush file data before changing attributes. Caller must hold any locks
* required to prevent further writes to this file until we're done setting
* flags.
*/
static inline int inode_drain_writes(struct inode *inode)
{
inode_dio_wait(inode);
return filemap_write_and_wait(inode->i_mapping);
}
#endif /* _LINUX_FS_H */

3
mm/filemap.c
View file

@ -2929,6 +2929,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
unsigned long limit = rlimit(RLIMIT_FSIZE);
loff_t pos;
if (IS_SWAPFILE(inode))
return -ETXTBSY;
if (!iov_iter_count(from))
return 0;

4
mm/memory.c
View file

@ -2385,6 +2385,10 @@ static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
if (vmf->vma->vm_file &&
IS_SWAPFILE(vmf->vma->vm_file->f_mapping->host))
return VM_FAULT_SIGBUS;
ret = vmf->vma->vm_ops->page_mkwrite(vmf);
/* Restore original flags so that caller is not surprised */
vmf->flags = old_flags;

8
mm/mmap.c
View file

@ -1457,8 +1457,12 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
case MAP_SHARED_VALIDATE:
if (flags & ~flags_mask)
return -EOPNOTSUPP;
if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
return -EACCES;
if (prot & PROT_WRITE) {
if (!(file->f_mode & FMODE_WRITE))
return -EACCES;
if (IS_SWAPFILE(file->f_mapping->host))
return -ETXTBSY;
}
/*
* Make sure we don't allow writing to an append-only

12
mm/swapfile.c
View file

@ -3268,6 +3268,17 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
if (error)
goto bad_swap;
/*
* Flush any pending IO and dirty mappings before we start using this
* swap device.
*/
inode->i_flags |= S_SWAPFILE;
error = inode_drain_writes(inode);
if (error) {
inode->i_flags &= ~S_SWAPFILE;
goto bad_swap;
}
mutex_lock(&swapon_mutex);
prio = -1;
if (swap_flags & SWAP_FLAG_PREFER)
@ -3288,7 +3299,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
atomic_inc(&proc_poll_event);
wake_up_interruptible(&proc_poll_wait);
inode->i_flags |= S_SWAPFILE;
error = 0;
goto out;
bad_swap: