linux-kernel - [PATCH] exec: fix linux_binprm::exec in transfer_args_to

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Message-Id: <20240320182607.1472887-1-jcmvbkbc@gmail.com>
Date: Wed, 20 Mar 2024 11:26:07 -0700
From: Max Filippov <jcmvbkbc@...il.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org,
	Eric Biederman <ebiederm@...ssion.com>,
	Kees Cook <keescook@...omium.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	Rich Felker <dalias@...c.org>,
	Max Filippov <jcmvbkbc@...il.com>,
	stable@...r.kernel.org
Subject: [PATCH] exec: fix linux_binprm::exec in transfer_args_to_stack()

In NUMMU kernel the value of linux_binprm::p is the offset inside the
temporary program arguments array maintained in separate pages in the
linux_binprm::page. linux_binprm::exec being a copy of linux_binprm::p
thus must be adjusted when that array is copied to the user stack.
Without that adjustment the value passed by the NOMMU kernel to the ELF
program in the AT_EXECFN entry of the aux array doesn't make any sense
and it may break programs that try to access memory pointed to by that
entry.

Adjust linux_binprm::exec before the successful return from the
transfer_args_to_stack().

Cc: stable@...r.kernel.org
Signed-off-by: Max Filippov <jcmvbkbc@...il.com>
---
 fs/exec.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/exec.c b/fs/exec.c
index af4fbb61cd53..5ee2545c3e18 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -895,6 +895,7 @@ int transfer_args_to_stack(struct linux_binprm *bprm,
 			goto out;
 	}

+	bprm->exec += *sp_location - MAX_ARG_PAGES * PAGE_SIZE;
 	*sp_location = sp;

 out:
-- 
2.39.2