Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex
From: Bernd Edlinger <hidden>
Date: 2020-03-13 01:06:04
Also in:
linux-api, linux-doc, linux-fsdevel, linux-mm, lkml
Subsystem:
exec & binfmt api, elf, filesystems (vfs and infrastructure), the rest · Maintainers:
Kees Cook, Alexander Viro, Christian Brauner, Linus Torvalds
Possibly related (same subject, not in this thread)
- 2020-03-12 · Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex · Kirill Tkhai <hidden>
- 2020-03-12 · Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex · Eric W. Biederman <hidden>
- 2020-03-12 · Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex · Kirill Tkhai <hidden>
- 2020-03-11 · Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex · Qian Cai <hidden>
- 2020-03-11 · Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex · Bernd Edlinger <hidden>
On 3/12/20 3:38 PM, Eric W. Biederman wrote:
Kirill Tkhai [off-list ref] writes:quoted
On 12.03.2020 15:24, Eric W. Biederman wrote:quoted
I actually need to switch the lock ordering here, and I haven't yet because my son was sick yesterday.
All the best wishes to you and your son. I hope he will get well soon. And sorry for not missing the issue in the review. The reason turns out that bprm_mm_init is called after prepare_bprm_creds, but there are error pathes between those where free_bprm is called up with cred != NULL and mm == NULL, but the mutex not locked. I figured out a possible fix for the problem that was pointed out: From ceb6f65b52b3a7f0280f4f20509a1564a439edf6 Mon Sep 17 00:00:00 2001 From: Bernd Edlinger <redacted> Date: Wed, 11 Mar 2020 15:31:07 +0100 Subject: [PATCH] Fix issues with exec_update_mutex Signed-off-by: Bernd Edlinger <redacted> --- fs/exec.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index ffeebb1..cde4937 100644
--- a/fs/exec.c
+++ b/fs/exec.c@@ -1021,8 +1021,14 @@ static int exec_mmap(struct mm_struct *mm) old_mm = current->mm; exec_mm_release(tsk, old_mm); - if (old_mm) { + if (old_mm) sync_mm_rss(old_mm); + + ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); + if (ret) + return ret; + + if (old_mm) { /* * Make sure that if there is a core dump in progress * for the old mm, we get out and die instead of going
@@ -1032,14 +1038,11 @@ static int exec_mmap(struct mm_struct *mm) down_read(&old_mm->mmap_sem); if (unlikely(old_mm->core_state)) { up_read(&old_mm->mmap_sem); + mutex_unlock(&tsk->signal->exec_update_mutex); return -EINTR; } } - ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); - if (ret) - return ret; - task_lock(tsk); active_mm = tsk->active_mm; membarrier_exec_mmap(mm);
@@ -1444,8 +1447,6 @@ static void free_bprm(struct linux_binprm *bprm) { free_arg_pages(bprm); if (bprm->cred) { - if (!bprm->mm) - mutex_unlock(¤t->signal->exec_update_mutex); mutex_unlock(¤t->signal->cred_guard_mutex); abort_creds(bprm->cred); }
@@ -1846,6 +1847,8 @@ static int __do_execve_file(int fd, struct filename *filename, would_dump(bprm, bprm->file); retval = exec_binprm(bprm); + if (bprm->cred && !bprm->mm) + mutex_unlock(¤t->signal->exec_update_mutex); if (retval < 0) goto out;
--
1.9.1