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Message-Id: <20180716165154.58794-1-jannh@google.com>
Date: Mon, 16 Jul 2018 18:51:54 +0200
From: Jann Horn <jannh@...gle.com>
To: Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...nel.dk>,
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>, linux-block@...r.kernel.org,
linux-scsi@...r.kernel.org, jannh@...gle.com
Cc: linux-kernel@...r.kernel.org, Douglas Gilbert <dgilbert@...erlog.com>,
Al Viro <viro@...iv.linux.org.uk>, jejb@...ux.vnet.ibm.com,
martin.petersen@...cle.com, kernel-hardening@...ts.openwall.com,
security@...nel.org, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH v4] bsg: mitigate read/write abuse, block uaccess in release
As Al Viro noted in commit 128394eff343 ("sg_write()/bsg_write() is not fit
to be called under KERNEL_DS"), bsg improperly accesses userspace
memory outside the provided buffer, permitting kernel memory corruption via
splice().
But bsg doesn't just do it on ->write(), also on ->read() and ->release().
As a band-aid, make sure that the ->read() and ->write() handlers can not
be called in weird contexts (kernel context or credentials different from
file opener), like for ib_safe_file_access().
Also, completely prevent user memory accesses in ->release() context.
Also put a deprecation warning in the read/write handlers.
This is similar to commit 26b5b874aff5 ("scsi: sg: mitigate read/write
abuse"), which deals with similar issues in /dev/sg*.
Fixes: 3d6392cfbd7d ("bsg: support for full generic block layer SG v3")
Cc: <stable@...r.kernel.org>
Signed-off-by: Jann Horn <jannh@...gle.com>
---
Resending for bsg as requested by Christoph Hellwig.
("PATCH v4" is a bit of a misnomer, but probably less confusing than
anything else I could have put in the subject line? Is there a canonical
way to deal with patch series that have been split up?)
changes:
- fix control flow in bsg_transport_complete_rq (v1 had a bug there)
- extract bsg part, since sg part has already landed separately
(Christoph Hellwig)
- put deprecation warning in read/write handlers, similar to Linus'
suggested patch for sg
block/bsg-lib.c | 7 +++++--
block/bsg.c | 43 ++++++++++++++++++++++++++++++++++---------
include/linux/bsg.h | 3 ++-
3 files changed, 41 insertions(+), 12 deletions(-)
diff --git a/block/bsg-lib.c b/block/bsg-lib.c
index 9419def8c017..e21f246526e2 100644
--- a/block/bsg-lib.c
+++ b/block/bsg-lib.c
@@ -53,7 +53,8 @@ static int bsg_transport_fill_hdr(struct request *rq, struct sg_io_v4 *hdr,
return 0;
}
-static int bsg_transport_complete_rq(struct request *rq, struct sg_io_v4 *hdr)
+static int bsg_transport_complete_rq(struct request *rq, struct sg_io_v4 *hdr,
+ bool cleaning_up)
{
struct bsg_job *job = blk_mq_rq_to_pdu(rq);
int ret = 0;
@@ -79,7 +80,9 @@ static int bsg_transport_complete_rq(struct request *rq, struct sg_io_v4 *hdr)
if (job->reply_len && hdr->response) {
int len = min(hdr->max_response_len, job->reply_len);
- if (copy_to_user(uptr64(hdr->response), job->reply, len))
+ if (cleaning_up)
+ ret = -EINVAL;
+ else if (copy_to_user(uptr64(hdr->response), job->reply, len))
ret = -EFAULT;
else
hdr->response_len = len;
diff --git a/block/bsg.c b/block/bsg.c
index 3da540faf673..deedce8c9ec2 100644
--- a/block/bsg.c
+++ b/block/bsg.c
@@ -21,6 +21,7 @@
#include <linux/idr.h>
#include <linux/bsg.h>
#include <linux/slab.h>
+#include <linux/cred.h> /* for bsg_check_file_access() */
#include <scsi/scsi.h>
#include <scsi/scsi_ioctl.h>
@@ -159,7 +160,8 @@ static int bsg_scsi_fill_hdr(struct request *rq, struct sg_io_v4 *hdr,
return 0;
}
-static int bsg_scsi_complete_rq(struct request *rq, struct sg_io_v4 *hdr)
+static int bsg_scsi_complete_rq(struct request *rq, struct sg_io_v4 *hdr,
+ bool cleaning_up)
{
struct scsi_request *sreq = scsi_req(rq);
int ret = 0;
@@ -179,7 +181,9 @@ static int bsg_scsi_complete_rq(struct request *rq, struct sg_io_v4 *hdr)
int len = min_t(unsigned int, hdr->max_response_len,
sreq->sense_len);
- if (copy_to_user(uptr64(hdr->response), sreq->sense, len))
+ if (cleaning_up)
+ ret = -EINVAL;
+ else if (copy_to_user(uptr64(hdr->response), sreq->sense, len))
ret = -EFAULT;
else
hdr->response_len = len;
@@ -381,11 +385,12 @@ static struct bsg_command *bsg_get_done_cmd(struct bsg_device *bd)
}
static int blk_complete_sgv4_hdr_rq(struct request *rq, struct sg_io_v4 *hdr,
- struct bio *bio, struct bio *bidi_bio)
+ struct bio *bio, struct bio *bidi_bio,
+ bool cleaning_up)
{
int ret;
- ret = rq->q->bsg_dev.ops->complete_rq(rq, hdr);
+ ret = rq->q->bsg_dev.ops->complete_rq(rq, hdr, cleaning_up);
if (rq->next_rq) {
blk_rq_unmap_user(bidi_bio);
@@ -451,7 +456,7 @@ static int bsg_complete_all_commands(struct bsg_device *bd)
break;
tret = blk_complete_sgv4_hdr_rq(bc->rq, &bc->hdr, bc->bio,
- bc->bidi_bio);
+ bc->bidi_bio, true);
if (!ret)
ret = tret;
@@ -486,7 +491,7 @@ __bsg_read(char __user *buf, size_t count, struct bsg_device *bd,
* bsg_complete_work() cannot do that for us
*/
ret = blk_complete_sgv4_hdr_rq(bc->rq, &bc->hdr, bc->bio,
- bc->bidi_bio);
+ bc->bidi_bio, false);
if (copy_to_user(buf, &bc->hdr, sizeof(bc->hdr)))
ret = -EFAULT;
@@ -523,6 +528,15 @@ static inline int err_block_err(int ret)
return 0;
}
+static int bsg_check_file_access(struct file *file, const char *caller)
+{
+ if (file->f_cred != current_real_cred())
+ return -EPERM;
+ if (uaccess_kernel())
+ return -EACCES;
+ return 0;
+}
+
static ssize_t
bsg_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
@@ -532,6 +546,13 @@ bsg_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
bsg_dbg(bd, "read %zd bytes\n", count);
+ pr_err_once("process %d (%s) does direct read on /dev/bsg/*\n",
+ task_tgid_vnr(current), current->comm);
+
+ ret = bsg_check_file_access(file, __func__);
+ if (ret)
+ return ret;
+
bsg_set_block(bd, file);
bytes_read = 0;
@@ -606,8 +627,12 @@ bsg_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
bsg_dbg(bd, "write %zd bytes\n", count);
- if (unlikely(uaccess_kernel()))
- return -EINVAL;
+ pr_err_once("process %d (%s) does direct write on /dev/bsg/*\n",
+ task_tgid_vnr(current), current->comm);
+
+ ret = bsg_check_file_access(file, __func__);
+ if (ret)
+ return ret;
bsg_set_block(bd, file);
@@ -857,7 +882,7 @@ static long bsg_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
at_head = (0 == (hdr.flags & BSG_FLAG_Q_AT_TAIL));
blk_execute_rq(bd->queue, NULL, rq, at_head);
- ret = blk_complete_sgv4_hdr_rq(rq, &hdr, bio, bidi_bio);
+ ret = blk_complete_sgv4_hdr_rq(rq, &hdr, bio, bidi_bio, false);
if (copy_to_user(uarg, &hdr, sizeof(hdr)))
return -EFAULT;
diff --git a/include/linux/bsg.h b/include/linux/bsg.h
index dac37b6e00ec..c22bc359552a 100644
--- a/include/linux/bsg.h
+++ b/include/linux/bsg.h
@@ -11,7 +11,8 @@ struct bsg_ops {
int (*check_proto)(struct sg_io_v4 *hdr);
int (*fill_hdr)(struct request *rq, struct sg_io_v4 *hdr,
fmode_t mode);
- int (*complete_rq)(struct request *rq, struct sg_io_v4 *hdr);
+ int (*complete_rq)(struct request *rq, struct sg_io_v4 *hdr,
+ bool cleaning_up);
void (*free_rq)(struct request *rq);
};
--
2.18.0.203.gfac676dfb9-goog
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