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authorMiklos Szeredi <mszeredi@redhat.com>2021-01-05 08:36:11 +0800
committerMiklos Szeredi <mszeredi@redhat.com>2021-01-28 10:22:48 +0100
commitb854cc659dcb80f172cb35dbedc15d39d49c383f (patch)
treea6e341ada6aa4808a949c043cad3e7d90cd168b8
parentf2b00be488730522d0fb7a8a5de663febdcefe0a (diff)
ovl: avoid deadlock on directory ioctl
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>
-rw-r--r--fs/overlayfs/readdir.c23
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);
}
}