cachefiles: flush all requests after setting CACHEFILES_DEAD

In ondemand mode, when the daemon is processing an open request, if the
kernel flags the cache as CACHEFILES_DEAD, the cachefiles_daemon_write()
will always return -EIO, so the daemon can't pass the copen to the kernel.
Then the kernel process that is waiting for the copen triggers a hung_task.

Since the DEAD state is irreversible, it can only be exited by closing
/dev/cachefiles. Therefore, after calling cachefiles_io_error() to mark
the cache as CACHEFILES_DEAD, if in ondemand mode, flush all requests to
avoid the above hungtask. We may still be able to read some of the cached
data before closing the fd of /dev/cachefiles.

Note that this relies on the patch that adds reference counting to the req,
otherwise it may UAF.

Fixes: c8383054506c ("cachefiles: notify the user daemon when looking up cookie")
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Link: https://lore.kernel.org/r/20240522114308.2402121-12-libaokun@huaweicloud.com
Acked-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index ccb7b707ea4b7643962e79c88129051081b65d7e..06cdf1a8a16f6a1359d770d1b591af9cc27f57b7 100644 (file)
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -133,7 +133,7 @@ static int cachefiles_daemon_open(struct inode *inode, struct file *file)
        return 0;
 }
 
-static void cachefiles_flush_reqs(struct cachefiles_cache *cache)
+void cachefiles_flush_reqs(struct cachefiles_cache *cache)
 {
        struct xarray *xa = &cache->reqs;
        struct cachefiles_req *req;

diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index 45c8bed6053834cbfc76f132709f1d93d704ce83..6845a90cdfcce90325fd7b5e2d9108a11509409c 100644 (file)
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -188,6 +188,7 @@ extern int cachefiles_has_space(struct cachefiles_cache *cache,
  * daemon.c
  */
 extern const struct file_operations cachefiles_daemon_fops;
+extern void cachefiles_flush_reqs(struct cachefiles_cache *cache);
 extern void cachefiles_get_unbind_pincount(struct cachefiles_cache *cache);
 extern void cachefiles_put_unbind_pincount(struct cachefiles_cache *cache);
 
@@ -426,6 +427,8 @@ do {                                                        \
        pr_err("I/O Error: " FMT"\n", ##__VA_ARGS__);   \
        fscache_io_error((___cache)->cache);            \
        set_bit(CACHEFILES_DEAD, &(___cache)->flags);   \
+       if (cachefiles_in_ondemand_mode(___cache))      \
+               cachefiles_flush_reqs(___cache);        \
 } while (0)
 
 #define cachefiles_io_error_obj(object, FMT, ...)                      \