[merged] vfs-allow-dedupe-of-user-owned-read-only-files.patch removed from -mm tree

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



The patch titled
     Subject: vfs: allow dedupe of user owned read-only files
has been removed from the -mm tree.  Its filename was
     vfs-allow-dedupe-of-user-owned-read-only-files.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: Mark Fasheh <mfasheh@xxxxxxx>
Subject: vfs: allow dedupe of user owned read-only files

Patch series "vfs: fix dedupe permission check", v6.

The following patches fix a couple of issues with the permission check we
do in vfs_dedupe_file_range().

The first patch expands our check to allow dedupe of a file if the user
owns it or otherwise would be allowed to write to it.

Current behavior is that we'll allow dedupe only if:

- the user is an admin (root)
- the user has the file open for write

This makes it impossible for a user to dedupe their own file set unless
they do it as root, or ensure that all files have write permission. 
There's a couple of duperemove bugs open for this:

https://github.com/markfasheh/duperemove/issues/129
https://github.com/markfasheh/duperemove/issues/86

The other problem we have is also related to forcing the user to open
target files for write - A process trying to exec a file currently being
deduped gets ETXTBUSY.  The answer (as above) is to allow them to open the
targets ro - root can already do this.  There was a patch from Adam
Borowski to fix this back in 2016:

https://lkml.org/lkml/2016/7/17/130

which I have incorporated into my changes.


The 2nd patch fixes our return code for permission denied to be EPERM. 
For some reason we're returning EINVAL - I think that's probably my fault.
At any rate, we need to be returning something descriptive of the actual
problem, otherwise callers see EINVAL and can't really make a valid
determination of what's gone wrong.

This has also popped up in duperemove, mostly in the form of cryptic error
messages.  Because this is a code returned to userspace, I did check the
other users of extent-same that I could find.  Both 'bees' and
'rust-btrfs' do the same as duperemove and simply report the error (as
they should).


One way I tested these patches was to make non-root owned files with
read-only permissions and see if I could dedupe them as the owning user. 
For example, the following script fails on an unpatched kernel and
succeeds with the patches applied.

  TESTDIR=/btrfs
  USER=mfasheh

  rm -f $TESTDIR/file*

  dd if=/dev/zero of=$TESTDIR/file1 count=1024 bs=1024
  dd if=/dev/zero of=$TESTDIR/file2 count=1024 bs=1024

  chown $USER $TESTDIR/file*
  chmod 444 $TESTDIR/file*

  # open file* for read and dedupe
  sudo -u $USER duperemove -Ad $TESTDIR/file*


Lastly, I have an update to the fi_deduperange manpage to reflect these
changes.


This patch (of 2):

The permission check in vfs_dedupe_file_range_one() is too coarse - We
only allow dedupe of the destination file if the user is root, or they
have the file open for write.

This effectively limits a non-root user from deduping their own read-only
files.  In addition, the write file descriptor that the user is forced to
hold open can prevent execution of files.  As file data during a dedupe
does not change, the behavior is unexpected and this has caused a number
of issue reports.  For an example, see:

https://github.com/markfasheh/duperemove/issues/129

So change the check so we allow dedupe on the target if:

- the root or admin is asking for it
- the process has write access
- the owner of the file is asking for the dedupe
- the process could get write access

That way users can open read-only and still get dedupe.

Link: http://lkml.kernel.org/r/20180910232118.14424-2-mfasheh@xxxxxxx
Signed-off-by: Mark Fasheh <mfasheh@xxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Cc: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 fs/read_write.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

--- a/fs/read_write.c~vfs-allow-dedupe-of-user-owned-read-only-files
+++ a/fs/read_write.c
@@ -1977,6 +1977,20 @@ out_error:
 }
 EXPORT_SYMBOL(vfs_dedupe_file_range_compare);
 
+/* Check whether we are allowed to dedupe the destination file */
+static bool allow_file_dedupe(struct file *file)
+{
+	if (capable(CAP_SYS_ADMIN))
+		return true;
+	if (file->f_mode & FMODE_WRITE)
+		return true;
+	if (uid_eq(current_fsuid(), file_inode(file)->i_uid))
+		return true;
+	if (!inode_permission(file_inode(file), MAY_WRITE))
+		return true;
+	return false;
+}
+
 int vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,
 			      struct file *dst_file, loff_t dst_pos, u64 len)
 {
@@ -1991,7 +2005,7 @@ int vfs_dedupe_file_range_one(struct fil
 		goto out_drop_write;
 
 	ret = -EINVAL;
-	if (!(capable(CAP_SYS_ADMIN) || (dst_file->f_mode & FMODE_WRITE)))
+	if (!allow_file_dedupe(dst_file))
 		goto out_drop_write;
 
 	ret = -EXDEV;
_

Patches currently in -mm which might be from mfasheh@xxxxxxx are





[Index of Archives]     [Kernel Archive]     [IETF Annouce]     [DCCP]     [Netdev]     [Networking]     [Security]     [Bugtraq]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux SCSI]

  Powered by Linux