From fb003a1bd60358c0ccee0145079de258a6cf0ba8 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Tue, 25 May 2021 12:37:35 -0700 Subject: 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(+) (limited to 'fs/proc') diff --git a/fs/proc/base.c b/fs/proc/base.c index 55ce0ee9c5c7..297ea12b3cfd 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2704,6 +2704,10 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf, void *page; int rv; + /* A task may only write when it was the opener. */ + if (file->f_cred != current_real_cred()) + return -EPERM; + rcu_read_lock(); task = pid_task(proc_pid(inode), PIDTYPE_PID); if (!task) { -- cgit v1.2.3