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vfs: strengthen checking of file range inputs to generic_remap_checks

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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: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
This commit is contained in:
Darrick J. Wong 2018-10-30 10:40:46 +11:00 committed by Dave Chinner
parent 2c5773f102
commit 9fd91a90cb
1 changed files with 52 additions and 32 deletions
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84
mm/filemap.c
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@ -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);
}
count = iov_iter_count(from);
ret = generic_write_check_limits(file, iocb->ki_pos, &count);
if (ret)
return ret;
/*
* 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;
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.