projects / thirdparty / kernel / stable-queue.git / blame
| Commit | Line | Data |
|---|---|---|
| 80ae7e1e GKH |
1 | From f6581f5b55141a95657ef5742cf6a6bfa20a109f Mon Sep 17 00:00:00 2001 |
| 2 | From: Jann Horn <jannh@google.com> | |
| 3 | Date: Wed, 29 May 2019 13:31:57 +0200 | |
| 4 | Subject: ptrace: restore smp_rmb() in __ptrace_may_access() | |
| 5 | ||
| 6 | From: Jann Horn <jannh@google.com> | |
| 7 | ||
| 8 | commit f6581f5b55141a95657ef5742cf6a6bfa20a109f upstream. | |
| 9 | ||
| 10 | Restore the read memory barrier in __ptrace_may_access() that was deleted | |
| 11 | a couple years ago. Also add comments on this barrier and the one it pairs | |
| 12 | with to explain why they're there (as far as I understand). | |
| 13 | ||
| 14 | Fixes: bfedb589252c ("mm: Add a user_ns owner to mm_struct and fix ptrace permission checks") | |
| 15 | Cc: stable@vger.kernel.org | |
| 16 | Acked-by: Kees Cook <keescook@chromium.org> | |
| 17 | Acked-by: Oleg Nesterov <oleg@redhat.com> | |
| 18 | Signed-off-by: Jann Horn <jannh@google.com> | |
| 19 | Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> | |
| 20 | Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> | |
| 21 | ||
| 22 | --- | |
| 23 | kernel/cred.c | 9 +++++++++ | |
| 24 | kernel/ptrace.c | 10 ++++++++++ | |
| 25 | 2 files changed, 19 insertions(+) | |
| 26 | ||
| 27 | --- a/kernel/cred.c | |
| 28 | +++ b/kernel/cred.c | |
| 29 | @@ -448,6 +448,15 @@ int commit_creds(struct cred *new) | |
| 30 | if (task->mm) | |
| 31 | set_dumpable(task->mm, suid_dumpable); | |
| 32 | task->pdeath_signal = 0; | |
| 33 | + /* | |
| 34 | + * If a task drops privileges and becomes nondumpable, | |
| 35 | + * the dumpability change must become visible before | |
| 36 | + * the credential change; otherwise, a __ptrace_may_access() | |
| 37 | + * racing with this change may be able to attach to a task it | |
| 38 | + * shouldn't be able to attach to (as if the task had dropped | |
| 39 | + * privileges without becoming nondumpable). | |
| 40 | + * Pairs with a read barrier in __ptrace_may_access(). | |
| 41 | + */ | |
| 42 | smp_wmb(); | |
| 43 | } | |
| 44 | ||
| 45 | --- a/kernel/ptrace.c | |
| 46 | +++ b/kernel/ptrace.c | |
| 47 | @@ -323,6 +323,16 @@ static int __ptrace_may_access(struct ta | |
| 48 | return -EPERM; | |
| 49 | ok: | |
| 50 | rcu_read_unlock(); | |
| 51 | + /* | |
| 52 | + * If a task drops privileges and becomes nondumpable (through a syscall | |
| 53 | + * like setresuid()) while we are trying to access it, we must ensure | |
| 54 | + * that the dumpability is read after the credentials; otherwise, | |
| 55 | + * we may be able to attach to a task that we shouldn't be able to | |
| 56 | + * attach to (as if the task had dropped privileges without becoming | |
| 57 | + * nondumpable). | |
| 58 | + * Pairs with a write barrier in commit_creds(). | |
| 59 | + */ | |
| 60 | + smp_rmb(); | |
| 61 | mm = task->mm; | |
| 62 | if (mm && | |
| 63 | ((get_dumpable(mm) != SUID_DUMP_USER) && |