[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>,
	"Marc-André Lureau" <marcandre.lureau@redhat.com>,
	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: Sat, 13 Jun 2020 21:19:40 -0400	[thread overview]
Message-ID: <20200614012001.18468-1-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 c4a0f26b2824..0e6d6717bf73 100644
--- a/arch/um/drivers/vector_user.c
+++ b/arch/um/drivers/vector_user.c
@@ -789,10 +789,12 @@ 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

