[RFC] scsi {add,remove}-single-device and /proc/scsi/scsi

Commit Message

Tony Battersby July 24, 2023, 8:43 p.m. UTC

I am trying to fix a bug in the parser for these commands:

echo "scsi add-single-device host channel id lun" > /proc/scsi/scsi
echo "scsi remove-single-device host channel id lun" > /proc/scsi/scsi

With the current parser, if you omit some of the fields (for example the
lun), then the kernel will usually fill in the missing parameters with a
0, but on rare occasion it might supply something else.  So my question
for linux-scsi is: does anyone rely on omitting some of the parameters
in the cmds above and expect the kernel to supply 0 for the missing
parameters (for example lun is often 0)?  If so, then I can make the
parser always supply a 0 for the missing parameters.  If not, then I can
make the parser return an error if there are paramters missing, on the
theory that guessing which device to add or remove is a bad idea.

Below is the patch to return an error for a missing parameter.  The
patch to use 0 instead of returning an error is similar but intead of
goto uses:

host    = (p < end) ? simple_strtoul(p, &p, 0) : 0;
channel = (p + 1 < end) ? simple_strtoul(p + 1, &p, 0) : 0;
id      = (p + 1 < end) ? simple_strtoul(p + 1, &p, 0) : 0;
lun     = (p + 1 < end) ? simple_strtoul(p + 1, &p, 0) : 0;

---

From 4f8f3291b18fddb2cf75581a2a2cf847fd2896a7 Mon Sep 17 00:00:00 2001
From: Tony Battersby <[e-mail]>
Date: Fri, 21 Jul 2023 11:12:27 -0400
Subject: [PATCH] scsi: core: fix parsing of scsi {add,remove}-single-device

When parsing the "scsi add-single-device" and
"scsi remove-single-device" commands written to /proc/scsi/scsi, make
sure the parser doesn't skip over the NUL string terminator and read
past the end of the user-supplied string.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: [e-mail]
Signed-off-by: Tony Battersby <[e-mail]>
---
 drivers/scsi/scsi_proc.c | 48 +++++++++++++++++++++++++++++++---------
 1 file changed, 37 insertions(+), 11 deletions(-)

Patch

diff --git a/drivers/scsi/scsi_proc.c b/drivers/scsi/scsi_proc.c
index 4a6eb1741be0..b27c8da83e62 100644
--- a/drivers/scsi/scsi_proc.c
+++ b/drivers/scsi/scsi_proc.c
@@ -406,7 +406,7 @@  static ssize_t proc_scsi_write(struct file *file, const char __user *buf,
 			       size_t length, loff_t *ppos)
 {
 	int host, channel, id, lun;
-	char *buffer, *p;
+	char *buffer, *end, *p;
 	int err;
 
 	if (!buf || length > PAGE_SIZE)
@@ -421,10 +421,14 @@  static ssize_t proc_scsi_write(struct file *file, const char __user *buf,
 		goto out;
 
 	err = -EINVAL;
-	if (length < PAGE_SIZE)
-		buffer[length] = '\0';
-	else if (buffer[PAGE_SIZE-1])
-		goto out;
+	if (length < PAGE_SIZE) {
+		end = buffer + length;
+		*end = '\0';
+	} else {
+		end = buffer + PAGE_SIZE - 1;
+		if (*end)
+			goto out;
+	}
 
 	/*
 	 * Usage: echo "scsi add-single-device 0 1 2 3" >/proc/scsi/scsi
@@ -432,11 +436,22 @@  static ssize_t proc_scsi_write(struct file *file, const char __user *buf,
 	 */
 	if (!strncmp("scsi add-single-device", buffer, 22)) {
 		p = buffer + 23;
+		if (p >= end)
+			goto out;
 
 		host = simple_strtoul(p, &p, 0);
-		channel = simple_strtoul(p + 1, &p, 0);
-		id = simple_strtoul(p + 1, &p, 0);
-		lun = simple_strtoul(p + 1, &p, 0);
+		if (++p >= end)
+			goto out;
+
+		channel = simple_strtoul(p, &p, 0);
+		if (++p >= end)
+			goto out;
+
+		id = simple_strtoul(p, &p, 0);
+		if (++p >= end)
+			goto out;
+
+		lun = simple_strtoul(p, &p, 0);
 
 		err = scsi_add_single_device(host, channel, id, lun);
 
@@ -446,11 +461,22 @@  static ssize_t proc_scsi_write(struct file *file, const char __user *buf,
 	 */
 	} else if (!strncmp("scsi remove-single-device", buffer, 25)) {
 		p = buffer + 26;
+		if (p >= end)
+			goto out;
 
 		host = simple_strtoul(p, &p, 0);
-		channel = simple_strtoul(p + 1, &p, 0);
-		id = simple_strtoul(p + 1, &p, 0);
-		lun = simple_strtoul(p + 1, &p, 0);
+		if (++p >= end)
+			goto out;
+
+		channel = simple_strtoul(p, &p, 0);
+		if (++p >= end)
+			goto out;
+
+		id = simple_strtoul(p, &p, 0);
+		if (++p >= end)
+			goto out;
+
+		lun = simple_strtoul(p, &p, 0);
 
 		err = scsi_remove_single_device(host, channel, id, lun);
 	}