From 8c01db7619f07c85c5cd81ec5eb83608b56c88f5 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Wed, 14 Nov 2018 13:55:09 -0800 Subject: 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: # v3.6+ Cc: Jann Horn Cc: Andy Lutomirski Signed-off-by: Eric Biggers Reviewed-by: Jann Horn Signed-off-by: Jiri Kosina --- drivers/hid/uhid.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'drivers/hid/uhid.c') 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 #include +#include #include #include #include @@ -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: -- cgit v1.2.3 From 4d26d1d1e8065bb3326a7c06d5d4698e581443a9 Mon Sep 17 00:00:00 2001 From: David Herrmann Date: Wed, 14 Nov 2018 14:16:42 +0100 Subject: Revert "HID: uhid: use strlcpy() instead of strncpy()" This reverts commit 336fd4f5f25157e9e8bd50e898a1bbcd99eaea46. Please note that `strlcpy()` does *NOT* do what you think it does. strlcpy() *ALWAYS* reads the full input string, regardless of the 'length' parameter. That is, if the input is not zero-terminated, strlcpy() will *READ* beyond input boundaries. It does this, because it always returns the size it *would* copy if the target was big enough, not the truncated size it actually copied. The original code was perfectly fine. The hid device is zero-initialized and the strncpy() functions copied up to n-1 characters. The result is always zero-terminated this way. This is the third time someone tried to replace strncpy with strlcpy in this function, and gets it wrong. I now added a comment that should at least make people reconsider. Signed-off-by: David Herrmann Signed-off-by: Jiri Kosina --- drivers/hid/uhid.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) (limited to 'drivers/hid/uhid.c') diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c index 051639c09f72..840634e0f1e3 100644 --- a/drivers/hid/uhid.c +++ b/drivers/hid/uhid.c @@ -497,12 +497,13 @@ static int uhid_dev_create2(struct uhid_device *uhid, goto err_free; } - len = min(sizeof(hid->name), sizeof(ev->u.create2.name)); - strlcpy(hid->name, ev->u.create2.name, len); - len = min(sizeof(hid->phys), sizeof(ev->u.create2.phys)); - strlcpy(hid->phys, ev->u.create2.phys, len); - len = min(sizeof(hid->uniq), sizeof(ev->u.create2.uniq)); - strlcpy(hid->uniq, ev->u.create2.uniq, len); + /* @hid is zero-initialized, strncpy() is correct, strlcpy() not */ + len = min(sizeof(hid->name), sizeof(ev->u.create2.name)) - 1; + strncpy(hid->name, ev->u.create2.name, len); + len = min(sizeof(hid->phys), sizeof(ev->u.create2.phys)) - 1; + strncpy(hid->phys, ev->u.create2.phys, len); + len = min(sizeof(hid->uniq), sizeof(ev->u.create2.uniq)) - 1; + strncpy(hid->uniq, ev->u.create2.uniq, len); hid->ll_driver = &uhid_hid_driver; hid->bus = ev->u.create2.bus; -- cgit v1.2.3