linux/fs/9p/vfs_dentry.c
Dominique Martinet c898afdc15 9p: add missing locking around taking dentry fid list
Fix a use-after-free on dentry's d_fsdata fid list when a thread
looks up a fid through dentry while another thread unlinks it:

UAF thread:
refcount_t: addition on 0; use-after-free.
 p9_fid_get linux/./include/net/9p/client.h:262
 v9fs_fid_find+0x236/0x280 linux/fs/9p/fid.c:129
 v9fs_fid_lookup_with_uid linux/fs/9p/fid.c:181
 v9fs_fid_lookup+0xbf/0xc20 linux/fs/9p/fid.c:314
 v9fs_vfs_getattr_dotl+0xf9/0x360 linux/fs/9p/vfs_inode_dotl.c:400
 vfs_statx+0xdd/0x4d0 linux/fs/stat.c:248

Freed by:
 p9_fid_destroy (inlined)
 p9_client_clunk+0xb0/0xe0 linux/net/9p/client.c:1456
 p9_fid_put linux/./include/net/9p/client.h:278
 v9fs_dentry_release+0xb5/0x140 linux/fs/9p/vfs_dentry.c:55
 v9fs_remove+0x38f/0x620 linux/fs/9p/vfs_inode.c:518
 vfs_unlink+0x29a/0x810 linux/fs/namei.c:4335

The problem is that d_fsdata was not accessed under d_lock, because
d_release() normally is only called once the dentry is otherwise no
longer accessible but since we also call it explicitly in v9fs_remove
that lock is required:
move the hlist out of the dentry under lock then unref its fids once
they are no longer accessible.

Fixes: 154372e67d ("fs/9p: fix create-unlink-getattr idiom")
Cc: stable@vger.kernel.org
Reported-by: Meysam Firouzi
Reported-by: Amirmohammad Eftekhar
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Message-ID: <20240521122947.1080227-1-asmadeus@codewreck.org>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
2024-05-23 20:29:09 +09:00

113 lines
2.5 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* This file contians vfs dentry ops for the 9P2000 protocol.
*
* Copyright (C) 2004 by Eric Van Hensbergen <ericvh@gmail.com>
* Copyright (C) 2002 by Ron Minnich <rminnich@lanl.gov>
*/
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/namei.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <net/9p/9p.h>
#include <net/9p/client.h>
#include "v9fs.h"
#include "v9fs_vfs.h"
#include "fid.h"
/**
* v9fs_cached_dentry_delete - called when dentry refcount equals 0
* @dentry: dentry in question
*
*/
static int v9fs_cached_dentry_delete(const struct dentry *dentry)
{
p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p)\n",
dentry, dentry);
/* Don't cache negative dentries */
if (d_really_is_negative(dentry))
return 1;
return 0;
}
/**
* v9fs_dentry_release - called when dentry is going to be freed
* @dentry: dentry that is being release
*
*/
static void v9fs_dentry_release(struct dentry *dentry)
{
struct hlist_node *p, *n;
struct hlist_head head;
p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p)\n",
dentry, dentry);
spin_lock(&dentry->d_lock);
hlist_move_list((struct hlist_head *)&dentry->d_fsdata, &head);
spin_unlock(&dentry->d_lock);
hlist_for_each_safe(p, n, &head)
p9_fid_put(hlist_entry(p, struct p9_fid, dlist));
}
static int v9fs_lookup_revalidate(struct dentry *dentry, unsigned int flags)
{
struct p9_fid *fid;
struct inode *inode;
struct v9fs_inode *v9inode;
if (flags & LOOKUP_RCU)
return -ECHILD;
inode = d_inode(dentry);
if (!inode)
goto out_valid;
v9inode = V9FS_I(inode);
if (v9inode->cache_validity & V9FS_INO_INVALID_ATTR) {
int retval;
struct v9fs_session_info *v9ses;
fid = v9fs_fid_lookup(dentry);
if (IS_ERR(fid))
return PTR_ERR(fid);
v9ses = v9fs_inode2v9ses(inode);
if (v9fs_proto_dotl(v9ses))
retval = v9fs_refresh_inode_dotl(fid, inode);
else
retval = v9fs_refresh_inode(fid, inode);
p9_fid_put(fid);
if (retval == -ENOENT)
return 0;
if (retval < 0)
return retval;
}
out_valid:
return 1;
}
const struct dentry_operations v9fs_cached_dentry_operations = {
.d_revalidate = v9fs_lookup_revalidate,
.d_weak_revalidate = v9fs_lookup_revalidate,
.d_delete = v9fs_cached_dentry_delete,
.d_release = v9fs_dentry_release,
};
const struct dentry_operations v9fs_dentry_operations = {
.d_delete = always_delete_dentry,
.d_release = v9fs_dentry_release,
};