From: NeilBrown Date: Mon, 3 Jul 2017 05:27:26 +0000 (+1000) Subject: NFS: guard against confused server in nfs_atomic_open() X-Git-Tag: v4.13-rc2~10^2~33 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=eaa2b82c3b3c938ab4635f8967d33f3e581da836;p=linux.git NFS: guard against confused server in nfs_atomic_open() 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 Signed-off-by: Anna Schumaker --- diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index 98b18aaf45c9..90bc4025ca3c 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -1431,8 +1431,10 @@ static int nfs_finish_open(struct nfs_open_context *ctx, err = finish_open(file, dentry, do_open, opened); if (err) goto out; - nfs_file_set_open_context(file, ctx); - + if (S_ISREG(file->f_path.dentry->d_inode->i_mode)) + nfs_file_set_open_context(file, ctx); + else + err = -ESTALE; out: return err; }