Commit 9fd91a90 authored by Darrick J. Wong's avatar Darrick J. Wong Committed by Dave Chinner
Browse files

vfs: strengthen checking of file range inputs to generic_remap_checks 



File range remapping, if allowed to run past the destination file's EOF,
is an optimization on a regular file write.  Regular file writes that
extend the file length are subject to various constraints which are not
checked by range cloning.

This is a correctness problem because we're never allowed to touch
ranges that the page cache can't support (s_maxbytes); we're not
supposed to deal with large offsets (MAX_NON_LFS) if O_LARGEFILE isn't
set; and we must obey resource limits (RLIMIT_FSIZE).

Therefore, add these checks to the new generic_remap_checks function so
that we curtail unexpected behavior.

Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: default avatarAmir Goldstein <amir73il@gmail.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarDave Chinner <david@fromorbit.com>
parent 2c5773f1

mm/filemap.c

+52 −32
Original line number Diff line number Diff line
@@ -2915,6 +2915,42 @@ struct page *read_cache_page_gfp(struct address_space *mapping, 
}

EXPORT_SYMBOL(read_cache_page_gfp);



/*

 * Don't operate on ranges the page cache doesn't support, and don't exceed the

 * LFS limits.  If pos is under the limit it becomes a short access.  If it

 * exceeds the limit we return -EFBIG.

 */

static int generic_access_check_limits(struct file *file, loff_t pos,

				       loff_t *count)

{

	struct inode *inode = file->f_mapping->host;

	loff_t max_size = inode->i_sb->s_maxbytes;



	if (!(file->f_flags & O_LARGEFILE))

		max_size = MAX_NON_LFS;



	if (unlikely(pos >= max_size))

		return -EFBIG;

	*count = min(*count, max_size - pos);

	return 0;

}



static int generic_write_check_limits(struct file *file, loff_t pos,

				      loff_t *count)

{

	loff_t limit = rlimit(RLIMIT_FSIZE);



	if (limit != RLIM_INFINITY) {

		if (pos >= limit) {

			send_sig(SIGXFSZ, current, 0);

			return -EFBIG;

		}

		*count = min(*count, limit - pos);

	}



	return generic_access_check_limits(file, pos, count);

}



/*

 * Performs necessary checks before doing a write

 *
@@ -2926,8 +2962,8 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from) 
{

	struct file *file = iocb->ki_filp;

	struct inode *inode = file->f_mapping->host;

	unsigned long limit = rlimit(RLIMIT_FSIZE);

	loff_t pos;

	loff_t count;

	int ret;



	if (!iov_iter_count(from))

		return 0;
@@ -2936,40 +2972,15 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from) 
	if (iocb->ki_flags & IOCB_APPEND)

		iocb->ki_pos = i_size_read(inode);



	pos = iocb->ki_pos;



	if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))

		return -EINVAL;



	if (limit != RLIM_INFINITY) {

		if (iocb->ki_pos >= limit) {

			send_sig(SIGXFSZ, current, 0);

			return -EFBIG;

		}

		iov_iter_truncate(from, limit - (unsigned long)pos);

	}



	/*

	 * LFS rule

	 */

	if (unlikely(pos + iov_iter_count(from) > MAX_NON_LFS &&

				!(file->f_flags & O_LARGEFILE))) {

		if (pos >= MAX_NON_LFS)

			return -EFBIG;

		iov_iter_truncate(from, MAX_NON_LFS - (unsigned long)pos);

	}



	/*

	 * Are we about to exceed the fs block limit ?

	 *

	 * If we have written data it becomes a short write.  If we have

	 * exceeded without writing data we send a signal and return EFBIG.

	 * Linus frestrict idea will clean these up nicely..

	 */

	if (unlikely(pos >= inode->i_sb->s_maxbytes))

		return -EFBIG;

	count = iov_iter_count(from);

	ret = generic_write_check_limits(file, iocb->ki_pos, &count);

	if (ret)

		return ret;



	iov_iter_truncate(from, inode->i_sb->s_maxbytes - pos);

	iov_iter_truncate(from, count);

	return iov_iter_count(from);

}

EXPORT_SYMBOL(generic_write_checks);
@@ -2991,6 +3002,7 @@ int generic_remap_checks(struct file *file_in, loff_t pos_in, 
	uint64_t bcount;

	loff_t size_in, size_out;

	loff_t bs = inode_out->i_sb->s_blocksize;

	int ret;



	/* The start of both ranges must be aligned to an fs block. */

	if (!IS_ALIGNED(pos_in, bs) || !IS_ALIGNED(pos_out, bs))
@@ -3014,6 +3026,14 @@ int generic_remap_checks(struct file *file_in, loff_t pos_in, 
		return -EINVAL;

	count = min(count, size_in - (uint64_t)pos_in);



	ret = generic_access_check_limits(file_in, pos_in, &count);

	if (ret)

		return ret;



	ret = generic_write_check_limits(file_out, pos_out, &count);

	if (ret)

		return ret;



	/*

	 * If the user wanted us to link to the infile's EOF, round up to the

	 * next block boundary for this check.

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