From: Zizhi Wo wozizhi@huawei.com
commit 31ad74b20227ce6b40910ff78b1c604e42975cf1 upstream.
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@huawei.com Link: https://lore.kernel.org/r/20241107110649.3980193-5-wozizhi@huawei.com Reviewed-by: David Howells dhowells@redhat.com Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Bin Lan lanbincn@qq.com --- fs/cachefiles/interface.c | 14 ++++++++++---- fs/cachefiles/ondemand.c | 30 ++++++++++++++++++++++++------ 2 files changed, 34 insertions(+), 10 deletions(-)
diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c index bde23e156a63..fd71775c703a 100644 --- a/fs/cachefiles/interface.c +++ b/fs/cachefiles/interface.c @@ -327,6 +327,8 @@ static void cachefiles_commit_object(struct cachefiles_object *object, static void cachefiles_clean_up_object(struct cachefiles_object *object, struct cachefiles_cache *cache) { + struct file *file; + if (test_bit(FSCACHE_COOKIE_RETIRED, &object->cookie->flags)) { if (!test_bit(CACHEFILES_OBJECT_USING_TMPFILE, &object->flags)) { cachefiles_see_object(object, cachefiles_obj_see_clean_delete); @@ -342,10 +344,14 @@ static void cachefiles_clean_up_object(struct cachefiles_object *object, }
cachefiles_unmark_inode_in_use(object, object->file); - if (object->file) { - fput(object->file); - object->file = NULL; - } + + spin_lock(&object->lock); + file = object->file; + object->file = NULL; + spin_unlock(&object->lock); + + if (file) + fput(file); }
/* diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c index d1a0264b08a6..3389a373faf6 100644 --- a/fs/cachefiles/ondemand.c +++ b/fs/cachefiles/ondemand.c @@ -61,20 +61,26 @@ 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; 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, &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); @@ -83,6 +89,8 @@ static ssize_t cachefiles_ondemand_fd_write_iter(struct kiocb *kiocb, kiocb->ki_pos += ret; }
+out: + fput(file); return ret; }
@@ -90,12 +98,22 @@ 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,