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authorEric Biggers <ebiggers@google.com>2018-11-14 13:55:09 -0800
committerJiri Kosina <jkosina@suse.cz>2018-11-19 14:25:15 +0100
commit8c01db7619f07c85c5cd81ec5eb83608b56c88f5 (patch)
treec9d6f98e9f9013c24985b5200728b97969fef2e3
parent0fd791841a6d67af1155a9c3de54dea51220721e (diff)
HID: uhid: forbid UHID_CREATE under KERNEL_DS or elevated privileges
When a UHID_CREATE command is written to the uhid char device, a copy_from_user() is done from a user pointer embedded in the command. When the address limit is KERNEL_DS, e.g. as is the case during sys_sendfile(), this can read from kernel memory. Alternatively, information can be leaked from a setuid binary that is tricked to write to the file descriptor. Therefore, forbid UHID_CREATE in these cases. No other commands in uhid_char_write() are affected by this bug and UHID_CREATE is marked as "obsolete", so apply the restriction to UHID_CREATE only rather than to uhid_char_write() entirely. Thanks to Dmitry Vyukov for adding uhid definitions to syzkaller and to Jann Horn for commit 9da3f2b740544 ("x86/fault: BUG() when uaccess helpers fault on kernel addresses"), allowing this bug to be found. Reported-by: syzbot+72473edc9bf4eb1c6556@syzkaller.appspotmail.com Fixes: d365c6cfd337 ("HID: uhid: add UHID_CREATE and UHID_DESTROY events") Cc: <stable@vger.kernel.org> # v3.6+ Cc: Jann Horn <jannh@google.com> Cc: Andy Lutomirski <luto@kernel.org> Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Jann Horn <jannh@google.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
-rw-r--r--drivers/hid/uhid.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 3c5507313606..051639c09f72 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -12,6 +12,7 @@
#include <linux/atomic.h>
#include <linux/compat.h>
+#include <linux/cred.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/hid.h>
@@ -722,6 +723,17 @@ static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
switch (uhid->input_buf.type) {
case UHID_CREATE:
+ /*
+ * 'struct uhid_create_req' contains a __user pointer which is
+ * copied from, so it's unsafe to allow this with elevated
+ * privileges (e.g. from a setuid binary) or via kernel_write().
+ */
+ if (file->f_cred != current_cred() || uaccess_kernel()) {
+ pr_err_once("UHID_CREATE from different security context by process %d (%s), this is not allowed.\n",
+ task_tgid_vnr(current), current->comm);
+ ret = -EACCES;
+ goto unlock;
+ }
ret = uhid_dev_create(uhid, &uhid->input_buf);
break;
case UHID_CREATE2: