linux-kernel - Re: [syzbot] linux-next boot error: WARNING in find

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Date:   Wed, 4 Aug 2021 19:00:37 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Luigi Rizzo <lrizzo@...gle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-next@...r.kernel.org, sfr@...b.auug.org.au,
        syzkaller-bugs@...glegroups.com,
        Kentaro Takeda <takedakn@...data.co.jp>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        syzbot <syzbot+dcb8a1e30879e0d60e8c@...kaller.appspotmail.com>
Subject: Re: [syzbot] linux-next boot error: WARNING in find_vma

On 2021/08/04 5:24, Andrew Morton wrote:
> Thanks.  I'm suspecting "Add mmap_assert_locked() annotations to
> find_vma*()" found an error in Tomoyo - tomoyo_dump_page() should be
> holding mmap_lock?

Yes, TOMOYO needs the same protection which get_arg_page() needs.
Please fold below diff into "mm/pagemap: add mmap_assert_locked() annotations to find_vma*()".

diff --git a/fs/exec.c b/fs/exec.c
index 816c7e347c9c..c982de69fab9 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -214,8 +214,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
 		gup_flags |= FOLL_WRITE;
 
 	/*
-	 * We are doing an exec().  'current' is the process
-	 * doing the exec and bprm->mm is the new process's mm.
+	 * We are doing an exec(). bprm->mm is the new process's mm.
 	 */
 	mmap_read_lock(bprm->mm);
 	ret = get_user_pages_remote(bprm->mm, pos, 1, gup_flags,
diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
index 98d985895ec8..31af29f669d2 100644
--- a/security/tomoyo/domain.c
+++ b/security/tomoyo/domain.c
@@ -897,6 +897,9 @@ bool tomoyo_dump_page(struct linux_binprm *bprm, unsigned long pos,
 		      struct tomoyo_page_dump *dump)
 {
 	struct page *page;
+#ifdef CONFIG_MMU
+	int ret;
+#endif
 
 	/* dump->data is released by tomoyo_find_next_domain(). */
 	if (!dump->data) {
@@ -909,11 +912,13 @@ bool tomoyo_dump_page(struct linux_binprm *bprm, unsigned long pos,
 	/*
 	 * This is called at execve() time in order to dig around
 	 * in the argv/environment of the new proceess
-	 * (represented by bprm).  'current' is the process doing
-	 * the execve().
+	 * (represented by bprm).
 	 */
-	if (get_user_pages_remote(bprm->mm, pos, 1,
-				FOLL_FORCE, &page, NULL, NULL) <= 0)
+	mmap_read_lock(bprm->mm);
+	ret = get_user_pages_remote(bprm->mm, pos, 1,
+				    FOLL_FORCE, &page, NULL, NULL);
+	mmap_read_unlock(bprm->mm);
+	if (ret <= 0)
 		return false;
 #else
 	page = bprm->page[pos / PAGE_SIZE];