Patch "cachefiles: flush all requests after setting CACHEFILES_DEAD" has been added to the 6.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    cachefiles: flush all requests after setting CACHEFILES_DEAD

to the 6.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cachefiles-flush-all-requests-after-setting-cachefil.patch
and it can be found in the queue-6.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5c89ce24677a374d4a64bd4958bb9f22f59c81ca
Author: Baokun Li <libaokun1@xxxxxxxxxx>
Date:   Wed May 22 19:43:07 2024 +0800

    cachefiles: flush all requests after setting CACHEFILES_DEAD
    
    [ Upstream commit 85e833cd7243bda7285492b0653c3abb1e2e757b ]
    
    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@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240522114308.2402121-12-libaokun@xxxxxxxxxxxxxxx
    Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
    Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index ccb7b707ea4b7..06cdf1a8a16f6 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 45c8bed605383..6845a90cdfcce 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, ...)			\