linux-kernel - [PATCH] lsm: check size of writes

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Message-ID: <20241216030213.246804-2-leocstone@gmail.com>
Date: Sun, 15 Dec 2024 19:02:11 -0800
From: Leo Stone <leocstone@...il.com>
To: syzbot+4eb7a741b3216020043a@...kaller.appspotmail.com
Cc: Leo Stone <leocstone@...il.com>,
	jmorris@...ei.org,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	mortonm@...omium.org,
	paul@...l-moore.com,
	serge@...lyn.com,
	syzkaller-bugs@...glegroups.com
Subject: [PATCH] lsm: check size of writes

syzbot attempts to write a buffer with a large size to a sysfs entry
with writes handled by safesetid_gid_file_write(), triggering a warning
in kmalloc.

Check the size specified for write buffers before allocating.

Reported-by: syzbot+4eb7a741b3216020043a@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4eb7a741b3216020043a
Signed-off-by: Leo Stone <leocstone@...il.com>
---
 security/safesetid/securityfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/safesetid/securityfs.c b/security/safesetid/securityfs.c
index 25310468bcdd..5eba4c7f8d9e 100644
--- a/security/safesetid/securityfs.c
+++ b/security/safesetid/securityfs.c
@@ -254,7 +254,7 @@ static ssize_t safesetid_gid_file_write(struct file *file,
 	if (!file_ns_capable(file, &init_user_ns, CAP_MAC_ADMIN))
 		return -EPERM;
 
-	if (*ppos != 0)
+	if (*ppos != 0 || len >= KMALLOC_MAX_SIZE)
 		return -EINVAL;
 
 	return handle_policy_update(file, buf, len, GID);
-- 
2.43.0