diff options
| author | Miklos Szeredi <mszeredi@redhat.com> | 2021-01-05 08:36:11 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-02-10 09:29:15 +0100 |
| commit | a66f82a1de028878bb158cfaac178f3a710ebdeb (patch) | |
| tree | e2f8607981cc6753e6b48c9b324ac353605f972c /fs | |
| parent | fb8caef7c020267ad30e868a5aeaa5da6ccf0c6e (diff) | |
ovl: avoid deadlock on directory ioctl
commit b854cc659dcb80f172cb35dbedc15d39d49c383f upstream.
The function ovl_dir_real_file() currently uses the inode lock to serialize
writes to the od->upperfile field.
However, this function will get called by ovl_ioctl_set_flags(), which
utilizes the inode lock too. In this case ovl_dir_real_file() will try to
claim a lock that is owned by a function in its call stack, which won't get
released before ovl_dir_real_file() returns.
Fix by replacing the open coded compare and exchange by an explicit atomic
op.
Fixes: 61536bed2149 ("ovl: support [S|G]ETFLAGS and FS[S|G]ETXATTR ioctls for directories")
Cc: stable@vger.kernel.org # v5.10
Reported-by: Icenowy Zheng <icenowy@aosc.io>
Tested-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/overlayfs/readdir.c | 23 |
1 files changed, 7 insertions, 16 deletions
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c index 01620ebae1bd..60d751f28fea 100644 --- a/fs/overlayfs/readdir.c +++ b/fs/overlayfs/readdir.c @@ -865,7 +865,7 @@ struct file *ovl_dir_real_file(const struct file *file, bool want_upper) struct ovl_dir_file *od = file->private_data; struct dentry *dentry = file->f_path.dentry; - struct file *realfile = od->realfile; + struct file *old, *realfile = od->realfile; if (!OVL_TYPE_UPPER(ovl_path_type(dentry))) return want_upper ? NULL : realfile; @@ -874,29 +874,20 @@ struct file *ovl_dir_real_file(const struct file *file, bool want_upper) * Need to check if we started out being a lower dir, but got copied up */ if (!od->is_upper) { - struct inode *inode = file_inode(file); - realfile = READ_ONCE(od->upperfile); if (!realfile) { struct path upperpath; ovl_path_upper(dentry, &upperpath); realfile = ovl_dir_open_realfile(file, &upperpath); + if (IS_ERR(realfile)) + return realfile; - inode_lock(inode); - if (!od->upperfile) { - if (IS_ERR(realfile)) { - inode_unlock(inode); - return realfile; - } - smp_store_release(&od->upperfile, realfile); - } else { - /* somebody has beaten us to it */ - if (!IS_ERR(realfile)) - fput(realfile); - realfile = od->upperfile; + old = cmpxchg_release(&od->upperfile, NULL, realfile); + if (old) { + fput(realfile); + realfile = old; } - inode_unlock(inode); } } |