At present, the object->file has the NULL pointer dereference problem in ondemand-mode. The root cause is that the allocated fd and object->file lifetime are inconsistent, and the user-space invocation to anon_fd uses object->file. Following is the process that triggers the issue: [write fd] [umount] cachefiles_ondemand_fd_write_iter fscache_cookie_state_machine cachefiles_withdraw_cookie if (!file) return -ENOBUFS cachefiles_clean_up_object cachefiles_unmark_inode_in_use fput(object->file) object->file = NULL // file NULL pointer dereference! __cachefiles_write(..., file, ...) Fix this issue by add an additional reference count to the object->file before write/llseek, and decrement after it finished. Fixes: c8383054506c ("cachefiles: notify the user daemon when looking up cookie") Signed-off-by: Zizhi Wo <wozizhi@xxxxxxxxxx> --- fs/cachefiles/interface.c | 3 +++ fs/cachefiles/ondemand.c | 30 ++++++++++++++++++++++++------ 2 files changed, 27 insertions(+), 6 deletions(-) diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c index 35ba2117a6f6..d30127ead911 100644 --- a/fs/cachefiles/interface.c +++ b/fs/cachefiles/interface.c @@ -342,10 +342,13 @@ static void cachefiles_clean_up_object(struct cachefiles_object *object, } cachefiles_unmark_inode_in_use(object, object->file); + + spin_lock(&object->lock); if (object->file) { fput(object->file); object->file = NULL; } + spin_unlock(&object->lock); } /* diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c index 38ca6dce8ef2..fe3de9ad57bf 100644 --- a/fs/cachefiles/ondemand.c +++ b/fs/cachefiles/ondemand.c @@ -60,20 +60,26 @@ static ssize_t cachefiles_ondemand_fd_write_iter(struct kiocb *kiocb, { struct cachefiles_object *object = kiocb->ki_filp->private_data; struct cachefiles_cache *cache = object->volume->cache; - struct file *file = object->file; + struct file *file; size_t len = iter->count, aligned_len = len; loff_t pos = kiocb->ki_pos; const struct cred *saved_cred; int ret; - if (!file) + spin_lock(&object->lock); + file = object->file; + if (!file) { + spin_unlock(&object->lock); return -ENOBUFS; + } + get_file(file); + spin_unlock(&object->lock); cachefiles_begin_secure(cache, &saved_cred); ret = __cachefiles_prepare_write(object, file, &pos, &aligned_len, len, true); cachefiles_end_secure(cache, saved_cred); if (ret < 0) - return ret; + goto out; trace_cachefiles_ondemand_fd_write(object, file_inode(file), pos, len); ret = __cachefiles_write(object, file, pos, iter, NULL, NULL); @@ -82,6 +88,8 @@ static ssize_t cachefiles_ondemand_fd_write_iter(struct kiocb *kiocb, kiocb->ki_pos += ret; } +out: + fput(file); return ret; } @@ -89,12 +97,22 @@ static loff_t cachefiles_ondemand_fd_llseek(struct file *filp, loff_t pos, int whence) { struct cachefiles_object *object = filp->private_data; - struct file *file = object->file; + struct file *file; + loff_t ret; - if (!file) + spin_lock(&object->lock); + file = object->file; + if (!file) { + spin_unlock(&object->lock); return -ENOBUFS; + } + get_file(file); + spin_unlock(&object->lock); - return vfs_llseek(file, pos, whence); + ret = vfs_llseek(file, pos, whence); + fput(file); + + return ret; } static long cachefiles_ondemand_fd_ioctl(struct file *filp, unsigned int ioctl, -- 2.39.2