Messages in this thread Patch in this message | | | From | Kees Cook <> | Subject | [PATCH] proc: Check /proc/$pid/attr/ writes against file opener | Date | Tue, 25 May 2021 12:37:35 -0700 |
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Fix another "confused deputy" weakness[1]. Writes to /proc/$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 <keescook@chromium.org> --- fs/proc/base.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/fs/proc/base.c b/fs/proc/base.c index 3851bfcdba56..58bbf334265b 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2703,6 +2703,10 @@ 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) { -- 2.25.1
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