A confused server could return a filehandle for an
NFSv4 OPEN request, which it previously returned for a directory.
So the inode returned by ->open_context() in nfs_atomic_open()
could conceivably be a directory inode.
This has particular implications for the call to
nfs_file_set_open_context() in nfs_finish_open().
If that is called on a directory inode, then the nfs_open_context
that gets stored in the filp->private_data will be linked to
nfs_inode->open_files.
When the directory is closed, nfs_closedir() will (ultimately)
free the ->private_data, but not unlink it from nfs_inode->open_files
(because it doesn't expect an nfs_open_context there).
Subsequently the memory could get used for something else and eventually
if the ->open_files list is walked, the walker will fall off the end and
crash.
So: change nfs_finish_open() to only call nfs_file_set_open_context()
for regular-file inodes.
This failure mode has been seen in a production setting (unknown NFS
server implementation). The kernel was v3.0 and the specific sequence
seen would not affect more recent kernels, but I think a risk is still
present, and caution is wise.
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
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