linux-kernel - [PATCH] Fix null pointer dereference in vector_user

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Message-Id: <20200610034314.9290-1-gaurav1086@gmail.com>
Date:   Tue,  9 Jun 2020 23:43:00 -0400
From:   Gaurav Singh <gaurav1086@...il.com>
To:     gaurav1086@...il.com, Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Alex Dewar <alex.dewar@....co.uk>,
        linux-um@...ts.infradead.org (open list:USER-MODE LINUX (UML)),
        linux-kernel@...r.kernel.org (open list),
        netdev@...r.kernel.org (open list:BPF (Safe dynamic programs and tools)),
        bpf@...r.kernel.org (open list:BPF (Safe dynamic programs and tools))
Subject: [PATCH] Fix null pointer dereference in vector_user_bpf

Signed-off-by: Gaurav Singh <gaurav1086@...il.com>

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.

---
 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