[PATCH] Fix null pointer dereference in vector_user_bpf

From: Gaurav Singh <gaurav1086@gmail.com>
To: gaurav1086@gmail.com, Jeff Dike <jdike@addtoit.com>,
	Richard Weinberger <richard@nod.at>,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Alex Dewar <alex.dewar@gmx.co.uk>,
	linux-um@lists.infradead.org (open list:USER-MODE LINUX (UML)),
	linux-kernel@vger.kernel.org (open list),
	netdev@vger.kernel.org (open list:BPF (Safe dynamic programs and
	tools)),
	bpf@vger.kernel.org (open list:BPF (Safe dynamic programs and
	tools))
Subject: [PATCH] Fix null pointer dereference in vector_user_bpf
Date: Wed, 10 Jun 2020 22:40:36 -0400	[thread overview]
Message-ID: <20200611024053.10429-1-gaurav1086@gmail.com> (raw)

The bpf_prog is being checked for !NULL after uml_kmalloc but
later its used directly for example:
bpf_prog->filter = bpf and is also later returned upon success.
Fix this, do a NULL check and return right away.

Signed-off-by: Gaurav Singh <gaurav1086@gmail.com>
---
 arch/um/drivers/vector_user.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/um/drivers/vector_user.c b/arch/um/drivers/vector_user.c
index aa28e9eecb7b..71d043ae306f 100644
--- a/arch/um/drivers/vector_user.c
+++ b/arch/um/drivers/vector_user.c
@@ -730,10 +730,12 @@ void *uml_vector_user_bpf(char *filename)
 		return false;
 	}
 	bpf_prog = uml_kmalloc(sizeof(struct sock_fprog), UM_GFP_KERNEL);
-	if (bpf_prog != NULL) {
-		bpf_prog->len = statbuf.st_size / sizeof(struct sock_filter);
-		bpf_prog->filter = NULL;
+	if (bpf_prog == NULL) {
+		printk(KERN_ERR "Failed to allocate bpf prog buffer");
+		return NULL;
 	}
+	bpf_prog->len = statbuf.st_size / sizeof(struct sock_filter);
+	bpf_prog->filter = NULL;
 	ffd = os_open_file(filename, of_read(OPENFLAGS()), 0);
 	if (ffd < 0) {
 		printk(KERN_ERR "Error %d opening bpf file", -errno);
-- 
2.17.1

