From bce9332220bd677d83b19d21502776ad555a0e73 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 5 Dec 2022 12:09:06 -0800
Subject: [PATCH] proc: proc_skip_spaces() shouldn't think it is working on C strings
Git-commit: bce9332220bd677d83b19d21502776ad555a0e73
Patch-mainline: v6.1
References: CVE-2022-4378 bsc#1206207

proc_skip_spaces() seems to think it is working on C strings, and ends
up being just a wrapper around skip_spaces() with a really odd calling
convention.

Instead of basing it on skip_spaces(), it should have looked more like
proc_skip_char(), which really is the exact same function (except it
skips a particular character, rather than whitespace).  So use that as
inspiration, odd coding and all.

Now the calling convention actually makes sense and works for the
intended purpose.

Reported-and-tested-by: Kyle Zeng <zengyhkyle@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 kernel/sysctl.c |   25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2169,13 +2169,14 @@ int proc_dostring(struct ctl_table *tabl
 			       (char __user *)buffer, lenp, ppos);
 }
 
-static size_t proc_skip_spaces(char **buf)
+static void proc_skip_spaces(char **buf, size_t *size)
 {
-	size_t ret;
-	char *tmp = skip_spaces(*buf);
-	ret = tmp - *buf;
-	*buf = tmp;
-	return ret;
+	while (*size) {
+		if (!isspace(**buf))
+			break;
+		(*size)--;
+		(*buf)++;
+	}
 }
 
 static void proc_skip_char(char **buf, size_t *size, const char v)
@@ -2412,7 +2413,7 @@ static int __do_proc_dointvec(void *tbl_
 		bool neg;
 
 		if (write) {
-			left -= proc_skip_spaces(&p);
+			proc_skip_spaces(&p, &left);
 
 			if (!left)
 				break;
@@ -2443,7 +2444,7 @@ static int __do_proc_dointvec(void *tbl_
 	if (!write && !first && left && !err)
 		err = proc_put_char(&buffer, &left, '\n');
 	if (write && !err && left)
-		left -= proc_skip_spaces(&p);
+		proc_skip_spaces(&p, &left);
 	if (write) {
 		kfree(kbuf);
 		if (first)
@@ -2492,7 +2493,7 @@ static int do_proc_douintvec_w(unsigned
 	if (IS_ERR(kbuf))
 		return -EINVAL;
 
-	left -= proc_skip_spaces(&p);
+	proc_skip_spaces(&p, &left);
 	if (!left) {
 		err = -EINVAL;
 		goto out_free;
@@ -2512,7 +2513,7 @@ static int do_proc_douintvec_w(unsigned
 	}
 
 	if (!err && left)
-		left -= proc_skip_spaces(&p);
+		proc_skip_spaces(&p, &left);
 
 out_free:
 	kfree(kbuf);
@@ -2926,7 +2927,7 @@ static int __do_proc_doulongvec_minmax(v
 		if (write) {
 			bool neg;
 
-			left -= proc_skip_spaces(&p);
+			proc_skip_spaces(&p, &left);
 			if (!left)
 				break;
 
@@ -2959,7 +2960,7 @@ static int __do_proc_doulongvec_minmax(v
 	if (!write && !first && left && !err)
 		err = proc_put_char(&buffer, &left, '\n');
 	if (write && !err)
-		left -= proc_skip_spaces(&p);
+		proc_skip_spaces(&p, &left);
 	if (write) {
 		kfree(kbuf);
 		if (first)