The function ovl_dir_real_file() currently uses the semaphore of the inode to synchronize write to the upperfile cache field.
However, this function will get called by ovl_ioctl_set_flags(), which utilizes the inode semaphore 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.
Define a dedicated semaphore for the upperfile cache, so that the deadlock won't happen.
Fixes: 61536bed2149 ("ovl: support [S|G]ETFLAGS and FS[S|G]ETXATTR ioctls for directories") Cc: stable@vger.kernel.org # v5.10 Signed-off-by: Icenowy Zheng icenowy@aosc.io --- fs/overlayfs/readdir.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c index 01620ebae1bd..f10701aabb71 100644 --- a/fs/overlayfs/readdir.c +++ b/fs/overlayfs/readdir.c @@ -56,6 +56,7 @@ struct ovl_dir_file { struct list_head *cursor; struct file *realfile; struct file *upperfile; + struct semaphore upperfile_sem; };
static struct ovl_cache_entry *ovl_cache_entry_from_node(struct rb_node *n) @@ -883,7 +884,7 @@ struct file *ovl_dir_real_file(const struct file *file, bool want_upper) ovl_path_upper(dentry, &upperpath); realfile = ovl_dir_open_realfile(file, &upperpath);
- inode_lock(inode); + down(&od->upperfile_sem); if (!od->upperfile) { if (IS_ERR(realfile)) { inode_unlock(inode); @@ -896,7 +897,7 @@ struct file *ovl_dir_real_file(const struct file *file, bool want_upper) fput(realfile); realfile = od->upperfile; } - inode_unlock(inode); + up(&od->upperfile_sem); } }
@@ -959,6 +960,7 @@ static int ovl_dir_open(struct inode *inode, struct file *file) od->realfile = realfile; od->is_real = ovl_dir_is_real(file->f_path.dentry); od->is_upper = OVL_TYPE_UPPER(type); + sema_init(&od->upperfile_sem, 1); file->private_data = od;
return 0;