From: Samuel Page fuse_add_dirent_to_cache() computes a serialized dirent size from the server-controlled namelen field and copies the dirent into a single page-cache page. The existing logic only checks whether the dirent fits in the remaining space of the current page and advances to a fresh page if not. It never checks whether the dirent itself exceeds PAGE_SIZE. As a result, a malicious FUSE server can return a dirent with namelen=4095, producing a serialized record size of 4120 bytes. On 4 KiB page systems this causes memcpy() to overflow the cache page by 24 bytes into the following kernel page. Reject dirents that cannot fit in a single page before copying them into the readdir cache. Fixes: 69e34551152a ("fuse: allow caching readdir") Cc: stable@vger.kernel.org # v6.16+ Assisted-by: Bynario AI Signed-off-by: Samuel Page Reported-by: Qi Tang Reported-by: Zijun Hu Signed-off-by: Miklos Szeredi --- fs/fuse/readdir.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/fuse/readdir.c b/fs/fuse/readdir.c index c88194e52d18..db5ae8ec1030 100644 --- a/fs/fuse/readdir.c +++ b/fs/fuse/readdir.c @@ -41,6 +41,10 @@ static void fuse_add_dirent_to_cache(struct file *file, unsigned int offset; void *addr; + /* Dirent doesn't fit in readdir cache page? Skip caching. */ + if (reclen > PAGE_SIZE) + return; + spin_lock(&fi->rdc.lock); /* * Is cache already completed? Or this entry does not go at the end of -- 2.53.0