[PATCH] lsm: check size of writes

[Leo Stone <leocstone@gmail.com>]

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@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4eb7a741b3216020043a
Signed-off-by: Leo Stone <leocstone@gmail.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