diff options
Diffstat (limited to 'meta-openbmc-mods/meta-common/recipes-kernel/linux/linux-aspeed/0109-signal-Extend-exec_id-to-64bits.patch')
| -rw-r--r-- | meta-openbmc-mods/meta-common/recipes-kernel/linux/linux-aspeed/0109-signal-Extend-exec_id-to-64bits.patch | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/meta-openbmc-mods/meta-common/recipes-kernel/linux/linux-aspeed/0109-signal-Extend-exec_id-to-64bits.patch b/meta-openbmc-mods/meta-common/recipes-kernel/linux/linux-aspeed/0109-signal-Extend-exec_id-to-64bits.patch new file mode 100644 index 000000000..7d879ab82 --- /dev/null +++ b/meta-openbmc-mods/meta-common/recipes-kernel/linux/linux-aspeed/0109-signal-Extend-exec_id-to-64bits.patch @@ -0,0 +1,88 @@ +From 5f2d04139aa5ed04eab54b84e8a25bab87a2449c Mon Sep 17 00:00:00 2001 +From: "Eric W. Biederman" <ebiederm@xmission.com> +Date: Mon, 30 Mar 2020 19:01:04 -0500 +Subject: [PATCH] signal: Extend exec_id to 64bits + +commit d1e7fd6462ca9fc76650fbe6ca800e35b24267da upstream. + +Replace the 32bit exec_id with a 64bit exec_id to make it impossible +to wrap the exec_id counter. With care an attacker can cause exec_id +wrap and send arbitrary signals to a newly exec'd parent. This +bypasses the signal sending checks if the parent changes their +credentials during exec. + +The severity of this problem can been seen that in my limited testing +of a 32bit exec_id it can take as little as 19s to exec 65536 times. +Which means that it can take as little as 14 days to wrap a 32bit +exec_id. Adam Zabrocki has succeeded wrapping the self_exe_id in 7 +days. Even my slower timing is in the uptime of a typical server. +Which means self_exec_id is simply a speed bump today, and if exec +gets noticably faster self_exec_id won't even be a speed bump. + +Extending self_exec_id to 64bits introduces a problem on 32bit +architectures where reading self_exec_id is no longer atomic and can +take two read instructions. Which means that is is possible to hit +a window where the read value of exec_id does not match the written +value. So with very lucky timing after this change this still +remains expoiltable. + +I have updated the update of exec_id on exec to use WRITE_ONCE +and the read of exec_id in do_notify_parent to use READ_ONCE +to make it clear that there is no locking between these two +locations. + +Link: https://lore.kernel.org/kernel-hardening/20200324215049.GA3710@pi3.com.pl +Fixes: 2.3.23pre2 +Cc: stable@vger.kernel.org +Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> +Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> +--- + fs/exec.c | 2 +- + include/linux/sched.h | 4 ++-- + kernel/signal.c | 2 +- + 3 files changed, 4 insertions(+), 4 deletions(-) + +diff --git a/fs/exec.c b/fs/exec.c +index c27231234764..fc2870f2aca9 100644 +--- a/fs/exec.c ++++ b/fs/exec.c +@@ -1383,7 +1383,7 @@ void setup_new_exec(struct linux_binprm * bprm) + + /* An exec changes our domain. We are no longer part of the thread + group */ +- current->self_exec_id++; ++ WRITE_ONCE(current->self_exec_id, current->self_exec_id + 1); + flush_signal_handlers(current, 0); + } + EXPORT_SYMBOL(setup_new_exec); +diff --git a/include/linux/sched.h b/include/linux/sched.h +index b968d736833b..5710b80f8050 100644 +--- a/include/linux/sched.h ++++ b/include/linux/sched.h +@@ -934,8 +934,8 @@ struct task_struct { + struct seccomp seccomp; + + /* Thread group tracking: */ +- u32 parent_exec_id; +- u32 self_exec_id; ++ u64 parent_exec_id; ++ u64 self_exec_id; + + /* Protection against (de-)allocation: mm, files, fs, tty, keyrings, mems_allowed, mempolicy: */ + spinlock_t alloc_lock; +diff --git a/kernel/signal.c b/kernel/signal.c +index eea748174ade..7d3d35eb7a0b 100644 +--- a/kernel/signal.c ++++ b/kernel/signal.c +@@ -1931,7 +1931,7 @@ bool do_notify_parent(struct task_struct *tsk, int sig) + * This is only possible if parent == real_parent. + * Check if it has changed security domain. + */ +- if (tsk->parent_exec_id != tsk->parent->self_exec_id) ++ if (tsk->parent_exec_id != READ_ONCE(tsk->parent->self_exec_id)) + sig = SIGCHLD; + } + +-- +2.7.4 + |