linux-kernel - [PATCH] exec: load_script: kill the onstack interp[BINPRM_BUF

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Message-ID: <20170918163446.GA26793@redhat.com>
Date:   Mon, 18 Sep 2017 18:34:46 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Ben Woodard <woodard@...hat.com>,
        Travis Gummels <tgummels@...hat.com>, tdhooge@...l.gov,
        linux-kernel@...r.kernel.org
Subject: [PATCH] exec: load_script: kill the onstack interp[BINPRM_BUF_SIZE]
 array

load_script() can simply use i_name instead, it points into bprm->buf[]
and nobody can change this memory until we call prepare_binprm().

The only complication is that we need to also change the signature of
bprm_change_interp() but this change looks good too.

While at it, do whitespace/style cleanups.

NOTE: the real motivation for this change is that people want to increase
BINPRM_BUF_SIZE, we need to change load_misc_binary() too but this looks
more complicated because afaics it is very buggy.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 fs/binfmt_script.c      | 17 +++++++++--------
 fs/exec.c               |  2 +-
 include/linux/binfmts.h |  2 +-
 3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index afdf4e3..7cde3f4 100644
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -19,7 +19,6 @@ static int load_script(struct linux_binprm *bprm)
 	const char *i_arg, *i_name;
 	char *cp;
 	struct file *file;
-	char interp[BINPRM_BUF_SIZE];
 	int retval;
 
 	if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
@@ -55,7 +54,7 @@ static int load_script(struct linux_binprm *bprm)
 			break;
 	}
 	for (cp = bprm->buf+2; (*cp == ' ') || (*cp == '\t'); cp++);
-	if (*cp == '\0') 
+	if (*cp == '\0')
 		return -ENOEXEC; /* No interpreter name found */
 	i_name = cp;
 	i_arg = NULL;
@@ -65,7 +64,6 @@ static int load_script(struct linux_binprm *bprm)
 		*cp++ = '\0';
 	if (*cp)
 		i_arg = cp;
-	strcpy (interp, i_name);
 	/*
 	 * OK, we've parsed out the interpreter name and
 	 * (optional) argument.
@@ -80,24 +78,27 @@ static int load_script(struct linux_binprm *bprm)
 	if (retval)
 		return retval;
 	retval = copy_strings_kernel(1, &bprm->interp, bprm);
-	if (retval < 0) return retval; 
+	if (retval < 0)
+		return retval;
 	bprm->argc++;
 	if (i_arg) {
 		retval = copy_strings_kernel(1, &i_arg, bprm);
-		if (retval < 0) return retval; 
+		if (retval < 0)
+			return retval;
 		bprm->argc++;
 	}
 	retval = copy_strings_kernel(1, &i_name, bprm);
-	if (retval) return retval; 
+	if (retval)
+		return retval;
 	bprm->argc++;
-	retval = bprm_change_interp(interp, bprm);
+	retval = bprm_change_interp(i_name, bprm);
 	if (retval < 0)
 		return retval;
 
 	/*
 	 * OK, now restart the process with the interpreter's dentry.
 	 */
-	file = open_exec(interp);
+	file = open_exec(i_name);
 	if (IS_ERR(file))
 		return PTR_ERR(file);
 
diff --git a/fs/exec.c b/fs/exec.c
index 01a9fb9..8a665ec 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1429,7 +1429,7 @@ static void free_bprm(struct linux_binprm *bprm)
 	kfree(bprm);
 }
 
-int bprm_change_interp(char *interp, struct linux_binprm *bprm)
+int bprm_change_interp(const char *interp, struct linux_binprm *bprm)
 {
 	/* If a binfmt changed the interp, free it first. */
 	if (bprm->interp != bprm->filename)
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index fb44d61..18d05b5 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -131,7 +131,7 @@ extern int setup_arg_pages(struct linux_binprm * bprm,
 			   int executable_stack);
 extern int transfer_args_to_stack(struct linux_binprm *bprm,
 				  unsigned long *sp_location);
-extern int bprm_change_interp(char *interp, struct linux_binprm *bprm);
+extern int bprm_change_interp(const char *interp, struct linux_binprm *bprm);
 extern int copy_strings_kernel(int argc, const char *const *argv,
 			       struct linux_binprm *bprm);
 extern int prepare_bprm_creds(struct linux_binprm *bprm);
-- 
2.5.0