[PATCH v4 4/9] vfs: remove redundant checks from generic_remap_checks()

Amir Goldstein
2019-05-31T16:47:18Z

The access limit checks on input file range in generic_remap_checks()
are redundant because the input file size is guaranteed to be within
limits and pos+len are already checked to be within input file size.

Beyond the fact that the check cannot fail, if it would have failed,
it could return -EFBIG for input file range error. There is no precedent
for that. -EFBIG is returned in syscalls that would change file length.

With that call removed, we can fold generic_access_check_limits() into
generic_write_check_limits().

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
---
mm/filemap.c | 33 ++++++++++++---------------------
1 file changed, 12 insertions(+), 21 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index a38619a4a6af..44361928bbb0 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2895,24 +2895,11 @@ EXPORT_SYMBOL(read_cache_page_gfp);
* 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)
{
+ struct inode *inode = file->f_mapping->host;
+ loff_t max_size = inode->i_sb->s_maxbytes;
loff_t limit = rlimit(RLIMIT_FSIZE);

if (limit != RLIM_INFINITY) {
@@ -2923,7 +2910,15 @@ static int generic_write_check_limits(struct file *file, loff_t pos,
*count = min(*count, limit - pos);
}

- return generic_access_check_limits(file, pos, count);
+ 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;
}

/*
@@ -2963,7 +2958,7 @@ EXPORT_SYMBOL(generic_write_checks);
/*
* Performs necessary checks before doing a clone.
*
- * Can adjust amount of bytes to clone.
+ * Can adjust amount of bytes to clone via @req_count argument.
* Returns appropriate error code that caller should return or
* zero in case the clone should be allowed.
*/
@@ -3001,10 +2996,6 @@ 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;
--
2.17.1