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Merge branch 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs

Browse source 
Pull overlayfs fixes from Miklos Szeredi:
 "This fixes a corner case for NFS exporting (introduced in this cycle)
  as well as fixing miscellaneous bugs"

* 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs:
  ovl: update Kconfig texts
  ovl: redirect_dir=nofollow should not follow redirect for opaque lower
  ovl: fix ptr_ret.cocci warnings
  ovl: check ERR_PTR() return value from ovl_lookup_real()
  ovl: check lower ancestry on encode of lower dir file handle
  ovl: hash non-dir by lower inode for fsnotify
This commit is contained in:
Linus Torvalds 2018-03-09 09:46:14 -08:00
commit 719ea86151
6 changed files with 233 additions and 73 deletions
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14
fs/overlayfs/Kconfig
View file

@ -24,6 +24,8 @@ config OVERLAY_FS_REDIRECT_DIR
an overlay which has redirects on a kernel that doesn't support this
feature will have unexpected results.
If unsure, say N.
config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW
bool "Overlayfs: follow redirects even if redirects are turned off"
default y
@ -32,8 +34,13 @@ config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW
Disable this to get a possibly more secure configuration, but that
might not be backward compatible with previous kernels.
If backward compatibility is not an issue, then it is safe and
recommended to say N here.
For more information, see Documentation/filesystems/overlayfs.txt
If unsure, say Y.
config OVERLAY_FS_INDEX
bool "Overlayfs: turn on inodes index feature by default"
depends on OVERLAY_FS
@ -51,6 +58,8 @@ config OVERLAY_FS_INDEX
That is, mounting an overlay which has an inodes index on a kernel
that doesn't support this feature will have unexpected results.
If unsure, say N.
config OVERLAY_FS_NFS_EXPORT
bool "Overlayfs: turn on NFS export feature by default"
depends on OVERLAY_FS
@ -72,3 +81,8 @@ config OVERLAY_FS_NFS_EXPORT
Note, that the NFS export feature is not backward compatible.
That is, mounting an overlay which has a full index on a kernel
that doesn't support this feature will have unexpected results.
Most users should say N here and enable this feature on a case-by-
case basis with the "nfs_export=on" mount option.
Say N unless you fully understand the consequences.

226
fs/overlayfs/export.c
View file

@ -19,6 +19,142 @@
#include <linux/ratelimit.h>
#include "overlayfs.h"
static int ovl_encode_maybe_copy_up(struct dentry *dentry)
{
int err;
if (ovl_dentry_upper(dentry))
return 0;
err = ovl_want_write(dentry);
if (!err) {
err = ovl_copy_up(dentry);
ovl_drop_write(dentry);
}
if (err) {
pr_warn_ratelimited("overlayfs: failed to copy up on encode (%pd2, err=%i)\n",
dentry, err);
}
return err;
}
/*
* Before encoding a non-upper directory file handle from real layer N, we need
* to check if it will be possible to reconnect an overlay dentry from the real
* lower decoded dentry. This is done by following the overlay ancestry up to a
* "layer N connected" ancestor and verifying that all parents along the way are
* "layer N connectable". If an ancestor that is NOT "layer N connectable" is
* found, we need to copy up an ancestor, which is "layer N connectable", thus
* making that ancestor "layer N connected". For example:
*
* layer 1: /a
* layer 2: /a/b/c
*
* The overlay dentry /a is NOT "layer 2 connectable", because if dir /a is
* copied up and renamed, upper dir /a will be indexed by lower dir /a from
* layer 1. The dir /a from layer 2 will never be indexed, so the algorithm (*)
* in ovl_lookup_real_ancestor() will not be able to lookup a connected overlay
* dentry from the connected lower dentry /a/b/c.
*
* To avoid this problem on decode time, we need to copy up an ancestor of
* /a/b/c, which is "layer 2 connectable", on encode time. That ancestor is
* /a/b. After copy up (and index) of /a/b, it will become "layer 2 connected"
* and when the time comes to decode the file handle from lower dentry /a/b/c,
* ovl_lookup_real_ancestor() will find the indexed ancestor /a/b and decoding
* a connected overlay dentry will be accomplished.
*
* (*) the algorithm in ovl_lookup_real_ancestor() can be improved to lookup an
* entry /a in the lower layers above layer N and find the indexed dir /a from
* layer 1. If that improvement is made, then the check for "layer N connected"
* will need to verify there are no redirects in lower layers above N. In the
* example above, /a will be "layer 2 connectable". However, if layer 2 dir /a
* is a target of a layer 1 redirect, then /a will NOT be "layer 2 connectable":
*
* layer 1: /A (redirect = /a)
* layer 2: /a/b/c
*/
/* Return the lowest layer for encoding a connectable file handle */
static int ovl_connectable_layer(struct dentry *dentry)
{
struct ovl_entry *oe = OVL_E(dentry);
/* We can get overlay root from root of any layer */
if (dentry == dentry->d_sb->s_root)
return oe->numlower;
/*
* If it's an unindexed merge dir, then it's not connectable with any
* lower layer
*/
if (ovl_dentry_upper(dentry) &&
!ovl_test_flag(OVL_INDEX, d_inode(dentry)))
return 0;
/* We can get upper/overlay path from indexed/lower dentry */
return oe->lowerstack[0].layer->idx;
}
/*
* @dentry is "connected" if all ancestors up to root or a "connected" ancestor
* have the same uppermost lower layer as the origin's layer. We may need to
* copy up a "connectable" ancestor to make it "connected". A "connected" dentry
* cannot become non "connected", so cache positive result in dentry flags.
*
* Return the connected origin layer or < 0 on error.
*/
static int ovl_connect_layer(struct dentry *dentry)
{
struct dentry *next, *parent = NULL;
int origin_layer;
int err = 0;
if (WARN_ON(dentry == dentry->d_sb->s_root) ||
WARN_ON(!ovl_dentry_lower(dentry)))
return -EIO;
origin_layer = OVL_E(dentry)->lowerstack[0].layer->idx;
if (ovl_dentry_test_flag(OVL_E_CONNECTED, dentry))
return origin_layer;
/* Find the topmost origin layer connectable ancestor of @dentry */
next = dget(dentry);
for (;;) {
parent = dget_parent(next);
if (WARN_ON(parent == next)) {
err = -EIO;
break;
}
/*
* If @parent is not origin layer connectable, then copy up
* @next which is origin layer connectable and we are done.
*/
if (ovl_connectable_layer(parent) < origin_layer) {
err = ovl_encode_maybe_copy_up(next);
break;
}
/* If @parent is connected or indexed we are done */
if (ovl_dentry_test_flag(OVL_E_CONNECTED, parent) ||
ovl_test_flag(OVL_INDEX, d_inode(parent)))
break;
dput(next);
next = parent;
}
dput(parent);
dput(next);
if (!err)
ovl_dentry_set_flag(OVL_E_CONNECTED, dentry);
return err ?: origin_layer;
}
/*
* We only need to encode origin if there is a chance that the same object was
* encoded pre copy up and then we need to stay consistent with the same
@ -41,73 +177,59 @@
* L = lower file handle
*
* (*) Connecting an overlay dir from real lower dentry is not always
* possible when there are redirects in lower layers. To mitigate this case,
* we copy up the lower dir first and then encode an upper dir file handle.
* possible when there are redirects in lower layers and non-indexed merge dirs.
* To mitigate those case, we may copy up the lower dir ancestor before encode
* a lower dir file handle.
*
* Return 0 for upper file handle, > 0 for lower file handle or < 0 on error.
*/
static bool ovl_should_encode_origin(struct dentry *dentry)
static int ovl_check_encode_origin(struct dentry *dentry)
{
struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
/* Upper file handle for pure upper */
if (!ovl_dentry_lower(dentry))
return false;
/*
* Decoding a merge dir, whose origin's parent is under a redirected
* lower dir is not always possible. As a simple aproximation, we do
* not encode lower dir file handles when overlay has multiple lower
* layers and origin is below the topmost lower layer.
*
* TODO: copy up only the parent that is under redirected lower.
*/
if (d_is_dir(dentry) && ofs->upper_mnt &&
OVL_E(dentry)->lowerstack[0].layer->idx > 1)
return false;
/* Decoding a non-indexed upper from origin is not implemented */
if (ovl_dentry_upper(dentry) &&
!ovl_test_flag(OVL_INDEX, d_inode(dentry)))
return false;
return true;
}
static int ovl_encode_maybe_copy_up(struct dentry *dentry)
{
int err;
if (ovl_dentry_upper(dentry))
return 0;
err = ovl_want_write(dentry);
if (err)
return err;
/*
* Upper file handle for non-indexed upper.
*
* Root is never indexed, so if there's an upper layer, encode upper for
* root.
*/
if (ovl_dentry_upper(dentry) &&
!ovl_test_flag(OVL_INDEX, d_inode(dentry)))
return 0;
err = ovl_copy_up(dentry);
/*
* Decoding a merge dir, whose origin's ancestor is under a redirected
* lower dir or under a non-indexed upper is not always possible.
* ovl_connect_layer() will try to make origin's layer "connected" by
* copying up a "connectable" ancestor.
*/
if (d_is_dir(dentry) && ofs->upper_mnt)
return ovl_connect_layer(dentry);
ovl_drop_write(dentry);
return err;
/* Lower file handle for indexed and non-upper dir/non-dir */
return 1;
}
static int ovl_d_to_fh(struct dentry *dentry, char *buf, int buflen)
{
struct dentry *origin = ovl_dentry_lower(dentry);
struct ovl_fh *fh = NULL;
int err;
int err, enc_lower;
/*
* If we should not encode a lower dir file handle, copy up and encode
* an upper dir file handle.
* Check if we should encode a lower or upper file handle and maybe
* copy up an ancestor to make lower file handle connectable.
*/
if (!ovl_should_encode_origin(dentry)) {
err = ovl_encode_maybe_copy_up(dentry);
if (err)
goto fail;
err = enc_lower = ovl_check_encode_origin(dentry);
if (enc_lower < 0)
goto fail;
origin = NULL;
}
/* Encode an upper or origin file handle */
fh = ovl_encode_fh(origin ?: ovl_dentry_upper(dentry), !origin);
/* Encode an upper or lower file handle */
fh = ovl_encode_fh(enc_lower ? ovl_dentry_lower(dentry) :
ovl_dentry_upper(dentry), !enc_lower);
err = PTR_ERR(fh);
if (IS_ERR(fh))
goto fail;
@ -355,8 +477,8 @@ static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
dput(upper);
}
if (!this)
return NULL;
if (IS_ERR_OR_NULL(this))
return this;
if (WARN_ON(ovl_dentry_real_at(this, layer->idx) != real)) {
dput(this);
@ -498,7 +620,7 @@ static struct dentry *ovl_lookup_real(struct super_block *sb,
if (err == -ECHILD) {
this = ovl_lookup_real_ancestor(sb, real,
layer);
err = IS_ERR(this) ? PTR_ERR(this) : 0;
err = PTR_ERR_OR_ZERO(this);
}
if (!err) {
dput(connected);

58
fs/overlayfs/inode.c
View file

@ -669,38 +669,59 @@ struct inode *ovl_lookup_inode(struct super_block *sb, struct dentry *real,
return inode;
}
/*
* Does overlay inode need to be hashed by lower inode?
*/
static bool ovl_hash_bylower(struct super_block *sb, struct dentry *upper,
struct dentry *lower, struct dentry *index)
{
struct ovl_fs *ofs = sb->s_fs_info;
/* No, if pure upper */
if (!lower)
return false;
/* Yes, if already indexed */
if (index)
return true;
/* Yes, if won't be copied up */
if (!ofs->upper_mnt)
return true;
/* No, if lower hardlink is or will be broken on copy up */
if ((upper || !ovl_indexdir(sb)) &&
!d_is_dir(lower) && d_inode(lower)->i_nlink > 1)
return false;
/* No, if non-indexed upper with NFS export */
if (sb->s_export_op && upper)
return false;
/* Otherwise, hash by lower inode for fsnotify */
return true;
}
struct inode *ovl_get_inode(struct super_block *sb, struct dentry *upperdentry,
struct dentry *lowerdentry, struct dentry *index,
unsigned int numlower)
{
struct ovl_fs *ofs = sb->s_fs_info;
struct inode *realinode = upperdentry ? d_inode(upperdentry) : NULL;
struct inode *inode;
/* Already indexed or could be indexed on copy up? */
bool indexed = (index || (ovl_indexdir(sb) && !upperdentry));
struct dentry *origin = indexed ? lowerdentry : NULL;
bool bylower = ovl_hash_bylower(sb, upperdentry, lowerdentry, index);
bool is_dir;
if (WARN_ON(upperdentry && indexed && !lowerdentry))
return ERR_PTR(-EIO);
if (!realinode)
realinode = d_inode(lowerdentry);
/*
* Copy up origin (lower) may exist for non-indexed non-dir upper, but
* we must not use lower as hash key in that case.
* Hash non-dir that is or could be indexed by origin inode.
* Hash dir that is or could be merged by origin inode.
* Hash pure upper and non-indexed non-dir by upper inode.
* Hash non-indexed dir by upper inode for NFS export.
* Copy up origin (lower) may exist for non-indexed upper, but we must
* not use lower as hash key if this is a broken hardlink.
*/
is_dir = S_ISDIR(realinode->i_mode);
if (is_dir && (indexed || !sb->s_export_op || !ofs->upper_mnt))
origin = lowerdentry;
if (upperdentry || origin) {
struct inode *key = d_inode(origin ?: upperdentry);
if (upperdentry || bylower) {
struct inode *key = d_inode(bylower ? lowerdentry :
upperdentry);
unsigned int nlink = is_dir ? 1 : realinode->i_nlink;
inode = iget5_locked(sb, (unsigned long) key,
@ -728,6 +749,7 @@ struct inode *ovl_get_inode(struct super_block *sb, struct dentry *upperdentry,
nlink = ovl_get_nlink(lowerdentry, upperdentry, nlink);
set_nlink(inode, nlink);
} else {
/* Lower hardlink that will be broken on copy up */
inode = new_inode(sb);
if (!inode)
goto out_nomem;

6
fs/overlayfs/namei.c
View file

@ -913,9 +913,6 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
stack[ctr].layer = lower.layer;
ctr++;
if (d.stop)
break;
/*
* Following redirects can have security consequences: it's like
* a symlink into the lower layer without the permission checks.
@ -933,6 +930,9 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
goto out_put;
}
if (d.stop)
break;
if (d.redirect && d.redirect[0] == '/' && poe != roe) {
poe = roe;
/* Find the current layer on the root dentry */

1
fs/overlayfs/overlayfs.h
View file

@ -40,6 +40,7 @@ enum ovl_inode_flag {
enum ovl_entry_flag {
OVL_E_UPPER_ALIAS,
OVL_E_OPAQUE,
OVL_E_CONNECTED,
};
/*

1
fs/overlayfs/super.c
View file

@ -1359,6 +1359,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
/* Root is always merge -> can have whiteouts */
ovl_set_flag(OVL_WHITEOUTS, d_inode(root_dentry));
ovl_dentry_set_flag(OVL_E_CONNECTED, root_dentry);
ovl_inode_init(d_inode(root_dentry), upperpath.dentry,
ovl_dentry_lower(root_dentry));