linux-kernel - [PATCH 5.1 06/55] fs/binfmt_flat.c: make load_flat_shared

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Message-Id: <20190702080124.380905163@linuxfoundation.org>
Date:   Tue,  2 Jul 2019 10:01:14 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jann Horn <jannh@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Russell King <linux@...linux.org.uk>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.1 06/55] fs/binfmt_flat.c: make load_flat_shared_library() work

From: Jann Horn <jannh@...gle.com>

commit 867bfa4a5fcee66f2b25639acae718e8b28b25a5 upstream.

load_flat_shared_library() is broken: It only calls load_flat_file() if
prepare_binprm() returns zero, but prepare_binprm() returns the number of
bytes read - so this only happens if the file is empty.

Instead, call into load_flat_file() if the number of bytes read is
non-negative. (Even if the number of bytes is zero - in that case,
load_flat_file() will see nullbytes and return a nice -ENOEXEC.)

In addition, remove the code related to bprm creds and stop using
prepare_binprm() - this code is loading a library, not a main executable,
and it only actually uses the members "buf", "file" and "filename" of the
linux_binprm struct. Instead, call kernel_read() directly.

Link: http://lkml.kernel.org/r/20190524201817.16509-1-jannh@google.com
Fixes: 287980e49ffc ("remove lots of IS_ERR_VALUE abuses")
Signed-off-by: Jann Horn <jannh@...gle.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Kees Cook <keescook@...omium.org>
Cc: Nicolas Pitre <nicolas.pitre@...aro.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Russell King <linux@...linux.org.uk>
Cc: Greg Ungerer <gerg@...ux-m68k.org>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/binfmt_flat.c |   23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -856,9 +856,14 @@ err:
 
 static int load_flat_shared_library(int id, struct lib_info *libs)
 {
+	/*
+	 * This is a fake bprm struct; only the members "buf", "file" and
+	 * "filename" are actually used.
+	 */
 	struct linux_binprm bprm;
 	int res;
 	char buf[16];
+	loff_t pos = 0;
 
 	memset(&bprm, 0, sizeof(bprm));
 
@@ -872,25 +877,11 @@ static int load_flat_shared_library(int
 	if (IS_ERR(bprm.file))
 		return res;
 
-	bprm.cred = prepare_exec_creds();
-	res = -ENOMEM;
-	if (!bprm.cred)
-		goto out;
-
-	/* We don't really care about recalculating credentials at this point
-	 * as we're past the point of no return and are dealing with shared
-	 * libraries.
-	 */
-	bprm.called_set_creds = 1;
-
-	res = prepare_binprm(&bprm);
+	res = kernel_read(bprm.file, bprm.buf, BINPRM_BUF_SIZE, &pos);
 
-	if (!res)
+	if (res >= 0)
 		res = load_flat_file(&bprm, libs, id, NULL);
 
-	abort_creds(bprm.cred);
-
-out:
 	allow_write_access(bprm.file);
 	fput(bprm.file);