linux.git/fs/overlayfs/export.c, branch v5.9

ovl: relax WARN_ON() when decoding lower directory file handle

2020-07-15T22:09:17+00:00

Decoding a lower directory file handle to overlay path with cold
inode/dentry cache may go as follows:

1. Decode real lower file handle to lower dir path
2. Check if lower dir is indexed (was copied up)
3. If indexed, get the upper dir path from index
4. Lookup upper dir path in overlay
5. If overlay path found, verify that overlay lower is the lower dir
   from step 1

On failure to verify step 5 above, user will get an ESTALE error and a
WARN_ON will be printed.

A mismatch in step 5 could be a result of lower directory that was renamed
while overlay was offline, after that lower directory has been copied up
and indexed.

This is a scripted reproducer based on xfstest overlay/052:

  # Create lower subdir
  create_dirs
  create_test_files $lower/lowertestdir/subdir
  mount_dirs
  # Copy up lower dir and encode lower subdir file handle
  touch $SCRATCH_MNT/lowertestdir
  test_file_handles $SCRATCH_MNT/lowertestdir/subdir -p -o $tmp.fhandle
  # Rename lower dir offline
  unmount_dirs
  mv $lower/lowertestdir $lower/lowertestdir.new/
  mount_dirs
  # Attempt to decode lower subdir file handle
  test_file_handles $SCRATCH_MNT -p -i $tmp.fhandle

Since this WARN_ON() can be triggered by user we need to relax it.

Fixes: 4b91c30a5a19 ("ovl: lookup connected ancestor of dir in inode cache")
Cc:  # v4.16+
Signed-off-by: Amir Goldstein 
Signed-off-by: Miklos Szeredi

ovl: add accessor for ofs->upper_mnt

2020-06-04T08:48:19+00:00

Next patch will remove ofs->upper_mnt, so add an accessor function for this
field.

Signed-off-by: Miklos Szeredi

ovl: return required buffer size for file handles

2020-05-13T09:11:24+00:00

Overlayfs doesn't work well with the fanotify mechanism.

Fanotify first probes for the required buffer size for the file handle,
but overlayfs currently bails out without passing the size back.

That results in errors in the kernel log, such as:

[527944.485384] overlayfs: failed to encode file handle (/, err=-75, buflen=0, len=29, type=1)
[527944.485386] fanotify: failed to encode fid (fsid=ae521e68.a434d95f, type=255, bytes=0, err=-2)

Signed-off-by: Lubos Dolezel 
Signed-off-by: Amir Goldstein 
Signed-off-by: Miklos Szeredi

ovl: potential crash in ovl_fid_to_fh()

2020-05-13T09:10:57+00:00

The "buflen" value comes from the user and there is a potential that it
could be zero.  In do_handle_to_path() we know that "handle->handle_bytes"
is non-zero and we do:

	handle_dwords = handle->handle_bytes >> 2;

So values 1-3 become zero.  Then in ovl_fh_to_dentry() we do:

	int len = fh_len << 2;

So now len is in the "0,4-128" range and a multiple of 4.  But if
"buflen" is zero it will try to copy negative bytes when we do the
memcpy in ovl_fid_to_fh().

	memcpy(&fh->fb, fid, buflen - OVL_FH_WIRE_OFFSET);

And that will lead to a crash.  Thanks to Amir Goldstein for his help
with this patch.

Fixes: cbe7fba8edfc ("ovl: make sure that real fid is 32bit aligned in memory")
Signed-off-by: Dan Carpenter 
Reviewed-by: Amir Goldstein 
Cc:  # v5.5
Signed-off-by: Miklos Szeredi

ovl: ovl_obtain_alias(): don't call d_instantiate_anon() for old

2020-03-17T14:04:23+00:00

The situation is the same as for __d_obtain_alias() (which is what that
thing is parallel to) - if we find a preexisting alias, we want to grab it,
drop the inode and return the alias we'd found.

The only thing d_instantiate_anon() does compared to that is spurious
security_d_instiate() that has already been done to that dentry with exact
same arguments.

Signed-off-by: Al Viro 
Signed-off-by: Miklos Szeredi

ovl: decide if revalidate needed on a per-dentry basis

2020-03-17T14:04:22+00:00

Allow completely skipping ->revalidate() on a per-dentry basis, in case the
underlying layers used for a dentry do not themselves have ->revalidate().

E.g. negative overlay dentry has no underlying layers, hence revalidate is
unnecessary.  Or if lower layer is remote but overlay dentry is pure-upper,
then can skip revalidate.

The following places need to update whether the dentry needs revalidate or
not:

 - fill-super (root dentry)
 - lookup
 - create
 - fh_to_dentry

Signed-off-by: Miklos Szeredi

ovl: layer is const

2020-01-24T08:46:45+00:00

The ovl_layer struct is never modified except at initialization.

Signed-off-by: Miklos Szeredi

ovl: generalize the lower_layers[] array

2020-01-22T19:11:41+00:00

Rename lower_layers[] array to layers[], extend its size by one and
initialize layers[0] with upper layer values.  Lower layers are now
addressed with index 1..numlower.  layers[0] is reserved even with lower
only overlay.

[SzM: replace ofs->numlower with ofs->numlayer, the latter's value is
incremented by one]

Signed-off-by: Amir Goldstein 
Signed-off-by: Miklos Szeredi

ovl: use pr_fmt auto generate prefix

2020-01-22T19:11:41+00:00

Use pr_fmt auto generate "overlayfs: " prefix.

Signed-off-by: lijiazi 
Signed-off-by: Miklos Szeredi

ovl: make sure that real fid is 32bit aligned in memory

2019-12-10T15:00:55+00:00

Seprate on-disk encoding from in-memory and on-wire resresentation
of overlay file handle.

In-memory and on-wire we only ever pass around pointers to struct
ovl_fh, which encapsulates at offset 3 the on-disk format struct
ovl_fb. struct ovl_fb encapsulates at offset 21 the real file handle.
That makes sure that the real file handle is always 32bit aligned
in-memory when passed down to the underlying filesystem.

On-disk format remains the same and store/load are done into
correctly aligned buffer.

New nfs exported file handles are exported with aligned real fid.
Old nfs file handles are copied to an aligned buffer before being
decoded.

Reported-by: Al Viro 
Signed-off-by: Amir Goldstein 
Signed-off-by: Miklos Szeredi