[PATCH v2 11/12] cachefiles: flush all requests after setting CACHEFILES_DEAD

libaokun
2024-05-15T08:56:44Z

From: Baokun Li <libaokun1@huawei.com>

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>
---
fs/cachefiles/daemon.c | 2 +-
fs/cachefiles/internal.h | 3 +++
2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index ccb7b707ea4b..06cdf1a8a16f 100644
--- 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 45c8bed60538..6845a90cdfcc 100644
--- 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, ...) \
--
2.39.2