linux-kernel - [PATCH v3] scsi: require CAP_SYS_ADMIN to write to procfs interface

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Date:   Sun,  5 Nov 2017 13:56:35 +1100
From:   Aleksa Sarai <asarai@...e.de>
To:     "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        containers@...ts.linux-foundation.org,
        Valentin Rothberg <vrothberg@...e.com>, cyphar@...har.com,
        Aleksa Sarai <asarai@...e.de>, stable@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH v3] scsi: require CAP_SYS_ADMIN to write to procfs interface

Previously, the only capability effectively required to operate on the
/proc/scsi interface was CAP_DAC_OVERRIDE (or for some other files,
having an fsuid of GLOBAL_ROOT_UID was enough). This means that
semi-privileged processes could interfere with core components of a
system (such as causing a DoS by removing the underlying SCSI device of
the host's / mount).

Cc: <stable@...r.kernel.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Aleksa Sarai <asarai@...e.de>
---
 drivers/scsi/scsi_proc.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_proc.c b/drivers/scsi/scsi_proc.c
index 480a597b3877..05d70e200c5f 100644
--- a/drivers/scsi/scsi_proc.c
+++ b/drivers/scsi/scsi_proc.c
@@ -27,6 +27,7 @@
 #include <linux/mutex.h>
 #include <linux/gfp.h>
 #include <linux/uaccess.h>
+#include <linux/capability.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_device.h>
@@ -51,7 +52,10 @@ static ssize_t proc_scsi_host_write(struct file *file, const char __user *buf,
 	struct Scsi_Host *shost = PDE_DATA(file_inode(file));
 	ssize_t ret = -ENOMEM;
 	char *page;
-    
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
 	if (count > PROC_BLOCK_SIZE)
 		return -EOVERFLOW;
 
@@ -313,6 +317,9 @@ static ssize_t proc_scsi_write(struct file *file, const char __user *buf,
 	char *buffer, *p;
 	int err;
 
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
 	if (!buf || length > PAGE_SIZE)
 		return -EINVAL;
 
-- 
2.14.3