Hi Mark, On Sun, Jun 20, 2021 at 10:44:29AM +0100, Mark Grant wrote: > Package: src:linux > Version: 4.19.194-1 > Severity: normal > > Dear Maintainer, > > After upgrading from linux-image-4.19.0-16-amd64 to > linux-image-4.19.0-17-amd64 > attaching an unprivileged linux container fails with the message: > lxc-attach: debian-buster-amd64-basic: lsm/lsm.c: lsm_process_label_set_at: > 174 > Operation not permitted - Failed to set AppArmor label "unconfined" > Rebooting into linux-image-4.19.0-16-amd64 with no other changes, the lxc > system works as expected.
I think this is the same issue as in #990072, would you be able to test the patch as commited https://salsa.debian.org/kernel-team/linux/-/commit/d3fc7c8514bed949d8797cfd3a50a1bed95629c0 ? Regards, Salvatore
From: Kees Cook <keesc...@chromium.org> Date: Tue, 8 Jun 2021 10:12:21 -0700 Subject: proc: Track /proc/$pid/attr/ opener mm_struct Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit?id=1f41b8f9577907fba56684231c7be89c8243d960 Bug-Debian: https://bugs.debian.org/990072 commit 591a22c14d3f45cc38bd1931c593c221df2f1881 upstream. Commit bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener") tried to make sure that there could not be a confusion between the opener of a /proc/$pid/attr/ file and the writer. It used struct cred to make sure the privileges didn't change. However, there were existing cases where a more privileged thread was passing the opened fd to a differently privileged thread (during container setup). Instead, use mm_struct to track whether the opener and writer are still the same process. (This is what several other proc files already do, though for different reasons.) Reported-by: Christian Brauner <christian.brau...@ubuntu.com> Reported-by: Andrea Righi <andrea.ri...@canonical.com> Tested-by: Andrea Righi <andrea.ri...@canonical.com> Fixes: bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener") Cc: sta...@vger.kernel.org Signed-off-by: Kees Cook <keesc...@chromium.org> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- fs/proc/base.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index bc736ea1192a..9f331abc202d 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2535,6 +2535,11 @@ static int proc_pident_readdir(struct file *file, struct dir_context *ctx, } #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) { @@ -2565,7 +2570,7 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf, int rv; /* 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; rcu_read_lock(); @@ -2613,9 +2618,11 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf, } 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[] = { -- 2.32.0
