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| author | Eric Biggers <ebiggers@google.com> | 2018-11-14 13:55:09 -0800 |
|---|---|---|
| committer | Jiri Kosina <jkosina@suse.cz> | 2018-11-19 14:25:15 +0100 |
| commit | 8c01db7619f07c85c5cd81ec5eb83608b56c88f5 (patch) | |
| tree | c9d6f98e9f9013c24985b5200728b97969fef2e3 | |
| parent | 0fd791841a6d67af1155a9c3de54dea51220721e (diff) | |
| download | linux-8c01db7619f07c85c5cd81ec5eb83608b56c88f5.tar.gz linux-8c01db7619f07c85c5cd81ec5eb83608b56c88f5.tar.bz2 linux-8c01db7619f07c85c5cd81ec5eb83608b56c88f5.zip | |
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.c | 12 |
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: |