[PATCH 5.4 26/57] dlmfs_file_write(): fix the bogosity in handling non-zero *ppos

Greg Kroah-Hartman
2020-05-04T18:10:46Z

From: Al Viro <viro@zeniv.linux.org.uk>

commit 3815f1be546e752327b5868af103ccdddcc4db77 upstream.

'count' is how much you want written, not the final position.
Moreover, it can legitimately be less than the current position...

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ocfs2/dlmfs/dlmfs.c | 27 ++++++++++++---------------
1 file changed, 12 insertions(+), 15 deletions(-)

--- a/fs/ocfs2/dlmfs/dlmfs.c
+++ b/fs/ocfs2/dlmfs/dlmfs.c
@@ -275,7 +275,6 @@ static ssize_t dlmfs_file_write(struct f
loff_t *ppos)
{
int bytes_left;
- ssize_t writelen;
char *lvb_buf;
struct inode *inode = file_inode(filp);

@@ -285,32 +284,30 @@ static ssize_t dlmfs_file_write(struct f
if (*ppos >= i_size_read(inode))
return -ENOSPC;

+ /* don't write past the lvb */
+ if (count > i_size_read(inode) - *ppos)
+ count = i_size_read(inode) - *ppos;
+
if (!count)
return 0;

if (!access_ok(buf, count))
return -EFAULT;

- /* don't write past the lvb */
- if ((count + *ppos) > i_size_read(inode))
- writelen = i_size_read(inode) - *ppos;
- else
- writelen = count - *ppos;
-
- lvb_buf = kmalloc(writelen, GFP_NOFS);
+ lvb_buf = kmalloc(count, GFP_NOFS);
if (!lvb_buf)
return -ENOMEM;

- bytes_left = copy_from_user(lvb_buf, buf, writelen);
- writelen -= bytes_left;
- if (writelen)
- user_dlm_write_lvb(inode, lvb_buf, writelen);
+ bytes_left = copy_from_user(lvb_buf, buf, count);
+ count -= bytes_left;
+ if (count)
+ user_dlm_write_lvb(inode, lvb_buf, count);

kfree(lvb_buf);

- *ppos = *ppos + writelen;
- mlog(0, "wrote %zd bytes\n", writelen);
- return writelen;
+ *ppos = *ppos + count;
+ mlog(0, "wrote %zu bytes\n", count);
+ return count;
}

static void dlmfs_init_once(void *foo)