From 5e910e1d0319bfbe85d9675aa3de2060b9ca5226 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Tue, 25 May 2021 12:37:35 -0700 Subject: [PATCH] proc: Check /proc/$pid/attr/ writes against file opener commit bfb819ea20ce8bbeeba17e1a6418bf8bda91fc28 upstream. Fix another "confused deputy" weakness[1]. Writes to /proc/$pid/attr/ files need to check the opener credentials, since these fds do not transition state across execve(). Without this, it is possible to trick another process (which may have different credentials) to write to its own /proc/$pid/attr/ files, leading to unexpected and possibly exploitable behaviors. [1] https://www.kernel.org/doc/html/latest/security/credentials.html?highlight=confused#open-file-credentials Fixes: 1da177e4c3f41 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Kees Cook Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/proc/base.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/proc/base.c b/fs/proc/base.c index 1649be692592..9c6ae6beb41c 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2523,6 +2523,10 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf, ssize_t length; struct task_struct *task = get_proc_task(inode); + /* A task may only write when it was the opener. */ + if (file->f_cred != current_real_cred()) + return -EPERM; + length = -ESRCH; if (!task) goto out_no_task;