From 0258b5fd7c7124b87e185a1a9322d2c66b1876b7 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Wed, 22 Sep 2021 11:24:02 -0500
Subject: coredump: Limit coredumps to a single thread group
Today when a signal is delivered with a handler of SIG_DFL whose
default behavior is to generate a core dump not only that process but
every process that shares the mm is killed.
In the case of vfork this looks like a real world problem. Consider
the following well defined sequence.
if (vfork() == 0) {
execve(...);
_exit(EXIT_FAILURE);
}
If a signal that generates a core dump is received after vfork but
before the execve changes the mm the process that called vfork will
also be killed (as the mm is shared).
Similarly if the execve fails after the point of no return the kernel
delivers SIGSEGV which will kill both the exec'ing process and because
the mm is shared the process that called vfork as well.
As far as I can tell this behavior is a violation of people's
reasonable expectations, POSIX, and is unnecessarily fragile when the
system is low on memory.
Solve this by making a userspace visible change to only kill a single
process/thread group. This is possible because Jann Horn recently
modified[1] the coredump code so that the mm can safely be modified
while the coredump is happening. With LinuxThreads long gone I don't
expect anyone to have a notice this behavior change in practice.
To accomplish this move the core_state pointer from mm_struct to
signal_struct, which allows different thread groups to coredump
simultatenously.
In zap_threads remove the work to kill anything except for the current
thread group.
v2: Remove core_state from the VM_BUG_ON_MM print to fix
compile failure when CONFIG_DEBUG_VM is enabled.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
[1] a07279c9a8cd ("binfmt_elf, binfmt_elf_fdpic: use a VMA list snapshot")
Fixes: d89f3847def4 ("[PATCH] thread-aware coredumps, 2.5.43-C3")
History-tree: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Link: https://lkml.kernel.org/r/87y27mvnke.fsf@disp2133
Link: https://lkml.kernel.org/r/20211007144701.67592574@canb.auug.org.au
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/binfmt_elf.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
(limited to 'fs/binfmt_elf.c')
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 69d900a8473d..796e5327ee7d 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1834,7 +1834,7 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
/*
* Allocate a structure for each thread.
*/
- for (ct = &dump_task->mm->core_state->dumper; ct; ct = ct->next) {
+ for (ct = &dump_task->signal->core_state->dumper; ct; ct = ct->next) {
t = kzalloc(offsetof(struct elf_thread_core_info,
notes[info->thread_notes]),
GFP_KERNEL);
@@ -2024,7 +2024,7 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
if (!elf_note_info_init(info))
return 0;
- for (ct = current->mm->core_state->dumper.next;
+ for (ct = current->signal->core_state->dumper.next;
ct; ct = ct->next) {
ets = kzalloc(sizeof(*ets), GFP_KERNEL);
if (!ets)
--
cgit