From: Baokun Li libaokun1@huawei.com

mainline inclusion from mainline-v6.9-rc3 commit 85e833cd7243bda7285492b0653c3abb1e2e757b category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IACZXJ CVE: CVE-2024-40935

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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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 Signed-off-by: Long Li leo.lilong@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 5f4df9588620..9072abfc154c 100644 --- a/fs/cachefiles/daemon.c +++ b/fs/cachefiles/daemon.c @@ -132,7 +132,7 @@ 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 2ad58c465208..e0a15150ed89 100644 --- a/fs/cachefiles/internal.h +++ b/fs/cachefiles/internal.h @@ -173,6 +173,7 @@ 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);

@@ -367,6 +368,8 @@ 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, ...) \