From: Kees Cook keescook@chromium.org
commit 591a22c14d3f45cc38bd1931c593c221df2f1881 upstream.
Commit bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener") tried to make sure that there could not be a confusion between the opener of a /proc/$pid/attr/ file and the writer. It used struct cred to make sure the privileges didn't change. However, there were existing cases where a more privileged thread was passing the opened fd to a differently privileged thread (during container setup). Instead, use mm_struct to track whether the opener and writer are still the same process. (This is what several other proc files already do, though for different reasons.)
Reported-by: Christian Brauner christian.brauner@ubuntu.com Reported-by: Andrea Righi andrea.righi@canonical.com Tested-by: Andrea Righi andrea.righi@canonical.com Fixes: bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener") Cc: stable@vger.kernel.org Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/proc/base.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
--- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2384,6 +2384,11 @@ out: }
#ifdef CONFIG_SECURITY +static int proc_pid_attr_open(struct inode *inode, struct file *file) +{ + return __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS); +} + static ssize_t proc_pid_attr_read(struct file * file, char __user * buf, size_t count, loff_t *ppos) { @@ -2414,7 +2419,7 @@ static ssize_t proc_pid_attr_write(struc 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()) + if (file->private_data != current->mm) return -EPERM;
length = -ESRCH; @@ -2455,9 +2460,11 @@ out_no_task: }
static const struct file_operations proc_pid_attr_operations = { + .open = proc_pid_attr_open, .read = proc_pid_attr_read, .write = proc_pid_attr_write, .llseek = generic_file_llseek, + .release = mem_release, };
static const struct pid_entry attr_dir_stuff[] = {