[PATCH] scsi: sg: fix v3 compat read/write interface

Arnd Bergmann
2019-12-04T14:08:28Z

In the v5.4 merge window, a cleanup patch from Al Viro conflicted
with my rework of the compat handling for sg.c read(). Linus Torvalds
did a correct merge but pointed out that the resulting code is still
unsatisfactory.

I later noticed that the sg_new_read() function still gets the compat
mode wrong, when the 'count' argument is large enough to pass a
compat_sg_io_hdr object, but not a nativ sg_io_hdr.

To address both of these, move the definition of compat_sg_io_hdr
into a scsi/sg.h to make it visible to sg.c and rewrite the logic
for reading req_pack_id as well as the size check to a simpler
version that gets the expected results.

Fixes: c35a5cfb4150 ("scsi: sg: sg_read(): simplify reading ->pack_id of userland sg_io_hdr_t")
Fixes: 98aaaec4a150 ("compat_ioctl: reimplement SG_IO handling")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
Not tested
---
block/scsi_ioctl.c | 29 +----------
drivers/scsi/sg.c | 126 +++++++++++++++++++++------------------------
include/scsi/sg.h | 30 +++++++++++
3 files changed, 91 insertions(+), 94 deletions(-)

diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index 650bade5ea5a..b61dbf4d8443 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -20,6 +20,7 @@
#include <scsi/scsi.h>
#include <scsi/scsi_ioctl.h>
#include <scsi/scsi_cmnd.h>
+#include <scsi/sg.h>

struct blk_cmd_filter {
unsigned long read_ok[BLK_SCSI_CMD_PER_LONG];
@@ -550,34 +551,6 @@ static inline int blk_send_start_stop(struct request_queue *q,
return __blk_send_generic(q, bd_disk, GPCMD_START_STOP_UNIT, data);
}

-#ifdef CONFIG_COMPAT
-struct compat_sg_io_hdr {
- compat_int_t interface_id; /* [i] 'S' for SCSI generic (required) */
- compat_int_t dxfer_direction; /* [i] data transfer direction */
- unsigned char cmd_len; /* [i] SCSI command length ( <= 16 bytes) */
- unsigned char mx_sb_len; /* [i] max length to write to sbp */
- unsigned short iovec_count; /* [i] 0 implies no scatter gather */
- compat_uint_t dxfer_len; /* [i] byte count of data transfer */
- compat_uint_t dxferp; /* [i], [*io] points to data transfer memory
- or scatter gather list */
- compat_uptr_t cmdp; /* [i], [*i] points to command to perform */
- compat_uptr_t sbp; /* [i], [*o] points to sense_buffer memory */
- compat_uint_t timeout; /* [i] MAX_UINT->no timeout (unit: millisec) */
- compat_uint_t flags; /* [i] 0 -> default, see SG_FLAG... */
- compat_int_t pack_id; /* [i->o] unused internally (normally) */
- compat_uptr_t usr_ptr; /* [i->o] unused internally */
- unsigned char status; /* [o] scsi status */
- unsigned char masked_status; /* [o] shifted, masked scsi status */
- unsigned char msg_status; /* [o] messaging level data (optional) */
- unsigned char sb_len_wr; /* [o] byte count actually written to sbp */
- unsigned short host_status; /* [o] errors from host adapter */
- unsigned short driver_status; /* [o] errors from software driver */
- compat_int_t resid; /* [o] dxfer_len - actual_transferred */
- compat_uint_t duration; /* [o] time taken by cmd (unit: millisec) */
- compat_uint_t info; /* [o] auxiliary information */
-};
-#endif
-
int put_sg_io_hdr(const struct sg_io_hdr *hdr, void __user *argp)
{
#ifdef CONFIG_COMPAT
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 160748ad9c0f..bc761059f1a8 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -405,6 +405,37 @@ sg_release(struct inode *inode, struct file *filp)
return 0;
}

+static int get_sg_io_pack_id(int *pack_id, void __user *buf, size_t count)
+{
+ struct sg_header __user *old_hdr = buf;
+ int reply_len;
+
+ if (count < SZ_SG_HEADER)
+ goto unknown_id;
+
+ /* negative reply_len means v3 format, otherwise v1/v2 */
+ if (get_user(reply_len, &old_hdr->reply_len))
+ return -EFAULT;
+ if (reply_len >= 0)
+ return get_user(*pack_id, &old_hdr->pack_id);
+
+#ifdef CONFIG_COMPAT
+ if (in_compat_syscall() && count >= sizeof(struct compat_sg_io_hdr)) {
+ struct compat_sg_io_hdr __user *hp = buf;
+ return get_user(*pack_id, &hp->pack_id);
+ }
+#endif
+ if (count >= sizeof(struct sg_io_hdr)) {
+ struct sg_io_hdr __user *hp = buf;
+ return get_user(*pack_id, &hp->pack_id);
+ }
+
+unknown_id:
+ /* no valid header was passed, so ignore the pack_id */
+ *pack_id = -1;
+ return 0;
+}
+
static ssize_t
sg_read(struct file *filp, char __user *buf, size_t count, loff_t * ppos)
{
@@ -413,8 +444,8 @@ sg_read(struct file *filp, char __user *buf, size_t count, loff_t * ppos)
Sg_request *srp;
int req_pack_id = -1;
sg_io_hdr_t *hp;
- struct sg_header *old_hdr = NULL;
- int retval = 0;
+ struct sg_header *old_hdr;
+ int retval;

/*
* This could cause a response to be stranded. Close the associated
@@ -429,79 +460,34 @@ sg_read(struct file *filp, char __user *buf, size_t count, loff_t * ppos)
SCSI_LOG_TIMEOUT(3, sg_printk(KERN_INFO, sdp,
"sg_read: count=%d\n", (int) count));

- if (sfp->force_packid && (count >= SZ_SG_HEADER)) {
- old_hdr = memdup_user(buf, SZ_SG_HEADER);
- if (IS_ERR(old_hdr))
- return PTR_ERR(old_hdr);
- if (old_hdr->reply_len < 0) {
- if (count >= SZ_SG_IO_HDR) {
- /*
- * This is stupid.
- *
- * We're copying the whole sg_io_hdr_t from user
- * space just to get the 'pack_id' field. But the
- * field is at different offsets for the compat
- * case, so we'll use "get_sg_io_hdr()" to copy
- * the whole thing and convert it.
- *
- * We could do something like just calculating the
- * offset based of 'in_compat_syscall()', but the
- * 'compat_sg_io_hdr' definition is in the wrong
- * place for that.
- */
- sg_io_hdr_t *new_hdr;
- new_hdr = kmalloc(SZ_SG_IO_HDR, GFP_KERNEL);
- if (!new_hdr) {
- retval = -ENOMEM;
- goto free_old_hdr;
- }
- retval = get_sg_io_hdr(new_hdr, buf);
- req_pack_id = new_hdr->pack_id;
- kfree(new_hdr);
- if (retval) {
- retval = -EFAULT;
- goto free_old_hdr;
- }
- }
- } else
- req_pack_id = old_hdr->pack_id;
- }
+ if (sfp->force_packid)
+ retval = get_sg_io_pack_id(&req_pack_id, buf, count);
+ if (retval)
+ return retval;
+
srp = sg_get_rq_mark(sfp, req_pack_id);
if (!srp) { /* now wait on packet to arrive */
- if (atomic_read(&sdp->detaching)) {
- retval = -ENODEV;
- goto free_old_hdr;
- }
- if (filp->f_flags & O_NONBLOCK) {
- retval = -EAGAIN;
- goto free_old_hdr;
- }
+ if (atomic_read(&sdp->detaching))
+ return -ENODEV;
+ if (filp->f_flags & O_NONBLOCK)
+ return -EAGAIN;
retval = wait_event_interruptible(sfp->read_wait,
(atomic_read(&sdp->detaching) ||
(srp = sg_get_rq_mark(sfp, req_pack_id))));
- if (atomic_read(&sdp->detaching)) {
- retval = -ENODEV;
- goto free_old_hdr;
- }
- if (retval) {
+ if (atomic_read(&sdp->detaching))
+ return -ENODEV;
+ if (retval)
/* -ERESTARTSYS as signal hit process */
- goto free_old_hdr;
- }
- }
- if (srp->header.interface_id != '\0') {
- retval = sg_new_read(sfp, buf, count, srp);
- goto free_old_hdr;
+ return retval;
}
+ if (srp->header.interface_id != '\0')
+ return sg_new_read(sfp, buf, count, srp);

hp = &srp->header;
- if (old_hdr == NULL) {
- old_hdr = kmalloc(SZ_SG_HEADER, GFP_KERNEL);
- if (! old_hdr) {
- retval = -ENOMEM;
- goto free_old_hdr;
- }
- }
- memset(old_hdr, 0, SZ_SG_HEADER);
+ old_hdr = kzalloc(SZ_SG_HEADER, GFP_KERNEL);
+ if (!old_hdr)
+ return -ENOMEM;
+
old_hdr->reply_len = (int) hp->timeout;
old_hdr->pack_len = old_hdr->reply_len; /* old, strange behaviour */
old_hdr->pack_id = hp->pack_id;
@@ -575,6 +561,14 @@ sg_new_read(Sg_fd * sfp, char __user *buf, size_t count, Sg_request * srp)
int err = 0, err2;
int len;

+#ifdef CONFIG_COMPAT
+ if (in_compat_syscall()) {
+ if (count < sizeof(struct compat_sg_io_hdr)) {
+ err = -EINVAL;
+ goto err_out;
+ }
+ } else
+#endif
if (count < SZ_SG_IO_HDR) {
err = -EINVAL;
goto err_out;
diff --git a/include/scsi/sg.h b/include/scsi/sg.h
index f91bcca604e4..c802739bde2f 100644
--- a/include/scsi/sg.h
+++ b/include/scsi/sg.h
@@ -68,6 +68,36 @@ typedef struct sg_io_hdr
unsigned int info; /* [o] auxiliary information */
} sg_io_hdr_t; /* 64 bytes long (on i386) */

+#if defined(__KERNEL__) && defined(CONFIG_COMPAT)
+#include <linux/compat.h>
+
+struct compat_sg_io_hdr {
+ compat_int_t interface_id; /* [i] 'S' for SCSI generic (required) */
+ compat_int_t dxfer_direction; /* [i] data transfer direction */
+ unsigned char cmd_len; /* [i] SCSI command length ( <= 16 bytes) */
+ unsigned char mx_sb_len; /* [i] max length to write to sbp */
+ unsigned short iovec_count; /* [i] 0 implies no scatter gather */
+ compat_uint_t dxfer_len; /* [i] byte count of data transfer */
+ compat_uint_t dxferp; /* [i], [*io] points to data transfer memory
+ or scatter gather list */
+ compat_uptr_t cmdp; /* [i], [*i] points to command to perform */
+ compat_uptr_t sbp; /* [i], [*o] points to sense_buffer memory */
+ compat_uint_t timeout; /* [i] MAX_UINT->no timeout (unit: millisec) */
+ compat_uint_t flags; /* [i] 0 -> default, see SG_FLAG... */
+ compat_int_t pack_id; /* [i->o] unused internally (normally) */
+ compat_uptr_t usr_ptr; /* [i->o] unused internally */
+ unsigned char status; /* [o] scsi status */
+ unsigned char masked_status; /* [o] shifted, masked scsi status */
+ unsigned char msg_status; /* [o] messaging level data (optional) */
+ unsigned char sb_len_wr; /* [o] byte count actually written to sbp */
+ unsigned short host_status; /* [o] errors from host adapter */
+ unsigned short driver_status; /* [o] errors from software driver */
+ compat_int_t resid; /* [o] dxfer_len - actual_transferred */
+ compat_uint_t duration; /* [o] time taken by cmd (unit: millisec) */
+ compat_uint_t info; /* [o] auxiliary information */
+};
+#endif
+
#define SG_INTERFACE_ID_ORIG 'S'

/* Use negative values to flag difference from original sg_header structure */
--
2.20.0