From patchwork Tue Jan 2 20:12:49 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 13509342 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3517516404; Tue, 2 Jan 2024 20:11:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EA8F3C433C7; Tue, 2 Jan 2024 20:11:48 +0000 (UTC) Date: Tue, 2 Jan 2024 15:12:49 -0500 From: Steven Rostedt To: LKML , Linux Trace Kernel Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , "Ubisectech Sirius" Subject: [PATCH v2] tracefs: Check for dentry->d_inode exists in set_gid() Message-ID: <20240102151249.05da244d@gandalf.local.home> X-Mailer: Claws Mail 3.19.1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: "Steven Rostedt (Google)" If a getdents() is called on the tracefs directory but does not get all the files, it can leave a "cursor" dentry in the d_subdirs list of tracefs dentry. This cursor dentry does not have a d_inode for it. Before referencing tracefs_inode from the dentry, the d_inode must first be checked if it has content. If not, then it's not a tracefs_inode and can be ignored. The following caused a crash: #define getdents64(fd, dirp, count) syscall(SYS_getdents64, fd, dirp, count) #define BUF_SIZE 256 #define TDIR "/tmp/file0" int main(void) { char buf[BUF_SIZE]; int fd; int n; mkdir(TDIR, 0777); mount(NULL, TDIR, "tracefs", 0, NULL); fd = openat(AT_FDCWD, TDIR, O_RDONLY); n = getdents64(fd, buf, BUF_SIZE); ret = mount(NULL, TDIR, NULL, MS_NOSUID|MS_REMOUNT|MS_RELATIME|MS_LAZYTIME, "gid=1000"); return 0; } That's because the 256 BUF_SIZE was not big enough to read all the dentries of the tracefs file system and it left a "cursor" dentry in the subdirs of the tracefs root inode. Then on remounting with "gid=1000", it would cause an iteration of all dentries which hit: ti = get_tracefs(dentry->d_inode); if (ti && (ti->flags & TRACEFS_EVENT_INODE)) eventfs_update_gid(dentry, gid); Which crashed because of the dereference of the cursor dentry which had a NULL d_inode. In the subdir loop of the dentry lookup of set_gid(), if a child has a NULL d_inode, simply skip it. Link: https://lore.kernel.org/all/20240102135637.3a21fb10@gandalf.local.home/ Cc: stable@vger.kernel.org Fixes: 7e8358edf503e ("eventfs: Fix file and directory uid and gid ownership") Reported-by: "Ubisectech Sirius" Signed-off-by: Steven Rostedt (Google) --- Changes since v1: https://lore.kernel.org/linux-trace-kernel/20240102142311.5670813d@gandalf.local.home - Simplify the logic to just continue the loop if the cursor dentry is hit. fs/tracefs/inode.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c index 62524b20964e..bc86ffdb103b 100644 --- a/fs/tracefs/inode.c +++ b/fs/tracefs/inode.c @@ -215,6 +215,10 @@ static void set_gid(struct dentry *parent, kgid_t gid) struct dentry *dentry = list_entry(tmp, struct dentry, d_child); next = tmp->next; + /* Note, getdents() can add a cursor dentry with no inode */ + if (!dentry->d_inode) + continue; + spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED); change_gid(dentry, gid);