linux-kernel - [RFC PATCH 2/5] mm: do not assume only the stack vma exists in setup_arg

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Date:   Mon, 27 Jul 2020 10:11:24 -0700
From:   Anthony Yznaga <anthony.yznaga@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-arch@...r.kernel.org
Cc:     mhocko@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org, arnd@...db.de,
        ebiederm@...ssion.com, keescook@...omium.org, gerg@...ux-m68k.org,
        ktkhai@...tuozzo.com, christian.brauner@...ntu.com,
        peterz@...radead.org, esyr@...hat.com, jgg@...pe.ca,
        christian@...lner.me, areber@...hat.com, cyphar@...har.com,
        steven.sistare@...cle.com
Subject: [RFC PATCH 2/5] mm: do not assume only the stack vma exists in setup_arg_pages()

In preparation for allowing vmas to be preserved across exec do not
assume that there is no prev vma to pass to mprotect_fixup() in
setup_arg_pages().
Also, setup_arg_pages() expands the initial stack of a process by
128k or to the stack size limit, whichever is smaller.  expand_stack()
assumes there is no vma between the vma passed to it and the
address to expand to, so check before calling it.

Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
---
 fs/exec.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index e6e8a9a70327..262112e5f9f8 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -720,7 +720,7 @@ int setup_arg_pages(struct linux_binprm *bprm,
 	unsigned long stack_shift;
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma = bprm->vma;
-	struct vm_area_struct *prev = NULL;
+	struct vm_area_struct *prev = vma->vm_prev;
 	unsigned long vm_flags;
 	unsigned long stack_base;
 	unsigned long stack_size;
@@ -819,6 +819,10 @@ int setup_arg_pages(struct linux_binprm *bprm,
 	else
 		stack_base = vma->vm_start - stack_expand;
 #endif
+	if (vma != find_vma(mm, stack_base)) {
+		ret = -EFAULT;
+		goto out_unlock;
+	}
 	current->mm->start_stack = bprm->p;
 	ret = expand_stack(vma, stack_base);
 	if (ret)
-- 
1.8.3.1