[PATCH v2] scsi: require CAP_SYS_ADMIN to write to procfs interface

From: Aleksa Sarai <asarai@suse.de>
To: "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
	containers@lists.linux-foundation.org,
	Valentin Rothberg <vrothberg@suse.com>,
	cyphar@cyphar.com, Aleksa Sarai <asarai@suse.de>,
	stable@vger.kernel.org,
	"Eric W. Biederman" <ebiederm@xmission.com>
Subject: [PATCH v2] scsi: require CAP_SYS_ADMIN to write to procfs interface
Date: Sun,  5 Nov 2017 07:26:24 +1100	[thread overview]
Message-ID: <20171104202624.6605-1-asarai@suse.de> (raw)

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@vger.kernel.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Aleksa Sarai <asarai@suse.de>
---
 drivers/scsi/scsi_proc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_proc.c b/drivers/scsi/scsi_proc.c
index 480a597b3877..8c891ab16b11 100644
--- a/drivers/scsi/scsi_proc.c
+++ b/drivers/scsi/scsi_proc.c
@@ -51,7 +51,10 @@ 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 +316,9 @@ 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
