linux-kernel - [PATCH 6/7] exec: Factor bprm_stack_limits out of prepare_arg

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Date:   Tue, 14 Jul 2020 08:31:03 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     <linux-kernel@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        <linux-fsdevel@...r.kernel.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        linux-security-module@...r.kernel.org,
        "Serge E. Hallyn" <serge@...lyn.com>,
        James Morris <jmorris@...ei.org>,
        Kentaro Takeda <takedakn@...data.co.jp>,
        Casey Schaufler <casey@...aufler-ca.com>,
        John Johansen <john.johansen@...onical.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: [PATCH 6/7] exec: Factor bprm_stack_limits out of prepare_arg_pages


In preparation for implementiong kernel_execve (which will take kernel
pointers not userspace pointers) factor out bprm_stack_limits out of
prepare_arg_pages.  This separates the counting which depends upon the
getting data from userspace from the calculations of the stack limits
which is usable in kernel_execve.

The remove prepare_args_pages and compute bprm->argc and bprm->envc
directly in do_execveat_common, before bprm_stack_limits is called.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/exec.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 50508892fa71..f8135dc149b3 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -448,19 +448,10 @@ static int count(struct user_arg_ptr argv, int max)
 	return i;
 }
 
-static int prepare_arg_pages(struct linux_binprm *bprm,
-			struct user_arg_ptr argv, struct user_arg_ptr envp)
+static int bprm_stack_limits(struct linux_binprm *bprm)
 {
 	unsigned long limit, ptr_size;
 
-	bprm->argc = count(argv, MAX_ARG_STRINGS);
-	if (bprm->argc < 0)
-		return bprm->argc;
-
-	bprm->envc = count(envp, MAX_ARG_STRINGS);
-	if (bprm->envc < 0)
-		return bprm->envc;
-
 	/*
 	 * Limit to 1/4 of the max stack size or 3/4 of _STK_LIM
 	 * (whichever is smaller) for the argv+env strings.
@@ -1964,7 +1955,17 @@ static int do_execveat_common(int fd, struct filename *filename,
 		goto out_ret;
 	}
 
-	retval = prepare_arg_pages(bprm, argv, envp);
+	retval = count(argv, MAX_ARG_STRINGS);
+	if (retval < 0)
+		goto out_free;
+	bprm->argc = retval;
+
+	retval = count(envp, MAX_ARG_STRINGS);
+	if (retval < 0)
+		goto out_free;
+	bprm->envc = retval;
+
+	retval = bprm_stack_limits(bprm);
 	if (retval < 0)
 		goto out_free;
 
-- 
2.25.0