[PATCH 4.2.y-ckt 06/53] atomic_open(): fix the handling of create_error

From: Kamal Mostafa
Date: Tue May 24 2016 - 13:55:55 EST

4.2.8-ckt11 -stable review patch. If anyone has any objections, please let me know.


From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

commit 10c64cea04d3c75c306b3f990586ffb343b63287 upstream.

* if we have a hashed negative dentry and either CREAT|EXCL on
r/o filesystem, or CREAT|TRUNC on r/o filesystem, or CREAT|EXCL
with failing may_o_create(), we should fail with EROFS or the
error may_o_create() has returned, but not ENOENT. Which is what
the current code ends up returning.

* if we have CREAT|TRUNC hitting a regular file on a read-only
filesystem, we can't fail with EROFS here. At the very least,
not until we'd done follow_managed() - we might have a writable
file (or a device, for that matter) bound on top of that one.
Moreover, the code downstream will see that O_TRUNC and attempt
to grab the write access (*after* following possible mount), so
if we really should fail with EROFS, it will happen. No need
to do that inside atomic_open().

The real logics is much simpler than what the current code is
trying to do - if we decided to go for simple lookup, ended
up with a negative dentry *and* had create_error set, fail with
create_error. No matter whether we'd got that negative dentry
from lookup_real() or had found it in dcache.

Acked-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
fs/namei.c | 20 ++++----------------
1 file changed, 4 insertions(+), 16 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 7f8e493..0402c3c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2909,22 +2909,10 @@ no_open:
dentry = lookup_real(dir, dentry, nd->flags);
if (IS_ERR(dentry))
return PTR_ERR(dentry);
- if (create_error) {
- int open_flag = op->open_flag;
- error = create_error;
- if ((open_flag & O_EXCL)) {
- if (!dentry->d_inode)
- goto out;
- } else if (!dentry->d_inode) {
- goto out;
- } else if ((open_flag & O_TRUNC) &&
- d_is_reg(dentry)) {
- goto out;
- }
- /* will fail later, go on to get the right error */
- }
+ }
+ if (create_error && !dentry->d_inode) {
+ error = create_error;
+ goto out;
path->dentry = dentry;