linux-kernel - [PATCH 5.10 121/199] proc_sysctl: fix oops caused by incorrect command parameters

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Message-Id: <20210125183221.332143557@linuxfoundation.org>
Date:   Mon, 25 Jan 2021 19:39:03 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xiaoming Ni <nixiaoming@...wei.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Michal Hocko <mhocko@...e.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.10 121/199] proc_sysctl: fix oops caused by incorrect command parameters

From: Xiaoming Ni <nixiaoming@...wei.com>

commit 697edcb0e4eadc41645fe88c991fe6a206b1a08d upstream.

The process_sysctl_arg() does not check whether val is empty before
invoking strlen(val).  If the command line parameter () is incorrectly
configured and val is empty, oops is triggered.

For example:
  "hung_task_panic=1" is incorrectly written as "hung_task_panic", oops is
  triggered. The call stack is as follows:
    Kernel command line: .... hung_task_panic
    ......
    Call trace:
    __pi_strlen+0x10/0x98
    parse_args+0x278/0x344
    do_sysctl_args+0x8c/0xfc
    kernel_init+0x5c/0xf4
    ret_from_fork+0x10/0x30

To fix it, check whether "val" is empty when "phram" is a sysctl field.
Error codes are returned in the failure branch, and error logs are
generated by parse_args().

Link: https://lkml.kernel.org/r/20210118133029.28580-1-nixiaoming@huawei.com
Fixes: 3db978d480e2843 ("kernel/sysctl: support setting sysctl parameters from kernel command line")
Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Cc: Luis Chamberlain <mcgrof@...nel.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Iurii Zaikin <yzaikin@...gle.com>
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Heiner Kallweit <hkallweit1@...il.com>
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: <stable@...r.kernel.org>	[5.8+]
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/proc/proc_sysctl.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -1770,6 +1770,12 @@ static int process_sysctl_arg(char *para
 			return 0;
 	}
 
+	if (!val)
+		return -EINVAL;
+	len = strlen(val);
+	if (len == 0)
+		return -EINVAL;
+
 	/*
 	 * To set sysctl options, we use a temporary mount of proc, look up the
 	 * respective sys/ file and write to it. To avoid mounting it when no
@@ -1811,7 +1817,6 @@ static int process_sysctl_arg(char *para
 				file, param, val);
 		goto out;
 	}
-	len = strlen(val);
 	wret = kernel_write(file, val, len, &pos);
 	if (wret < 0) {
 		err = wret;