linux-kernel - [PATCH v2] lsm: check size of writes

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Message-ID: <20241217182657.10080-2-leocstone@gmail.com>
Date: Tue, 17 Dec 2024 10:26:57 -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 v2] lsm: check size of writes

syzbot attempts to write a buffer with a large size to a sysfs entry
with writes handled by handle_policy_update(), 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>
---
v2: Make the check in handle_policy_update() to also cover
safesetid_uid_file_write(). Thanks for your feedback.
v1: https://lore.kernel.org/all/20241216030213.246804-2-leocstone@gmail.com/
---
 security/safesetid/securityfs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/security/safesetid/securityfs.c b/security/safesetid/securityfs.c
index 25310468bcdd..8e1ffd70b18a 100644
--- a/security/safesetid/securityfs.c
+++ b/security/safesetid/securityfs.c
@@ -143,6 +143,9 @@ static ssize_t handle_policy_update(struct file *file,
 	char *buf, *p, *end;
 	int err;
 
+	if (len >= KMALLOC_MAX_SIZE)
+		return -EINVAL;
+
 	pol = kmalloc(sizeof(struct setid_ruleset), GFP_KERNEL);
 	if (!pol)
 		return -ENOMEM;
-- 
2.43.0