wifi: wext: use flex array destination for memcpy()

commit e3e6e1d16a4cf7b63159ec71774e822194071954 upstream.

Syzkaller reports buffer overflow false positive as follows:
------------[ cut here ]------------
memcpy: detected field-spanning write (size 8) of single field
	"&compat_event->pointer" at net/wireless/wext-core.c:623 (size 4)
WARNING: CPU: 0 PID: 3607 at net/wireless/wext-core.c:623
	wireless_send_event+0xab5/0xca0 net/wireless/wext-core.c:623
Modules linked in:
CPU: 1 PID: 3607 Comm: syz-executor659 Not tainted
	6.0.0-rc6-next-20220921-syzkaller #0
[...]
Call Trace:
 <TASK>
 ioctl_standard_call+0x155/0x1f0 net/wireless/wext-core.c:1022
 wireless_process_ioctl+0xc8/0x4c0 net/wireless/wext-core.c:955
 wext_ioctl_dispatch net/wireless/wext-core.c:988 [inline]
 wext_ioctl_dispatch net/wireless/wext-core.c:976 [inline]
 wext_handle_ioctl+0x26b/0x280 net/wireless/wext-core.c:1049
 sock_ioctl+0x285/0x640 net/socket.c:1220
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
 [...]
 </TASK>

Wireless events will be sent on the appropriate channels in
wireless_send_event(). Different wireless events may have different
payload structure and size, so kernel uses **len** and **cmd** field
in struct __compat_iw_event as wireless event common LCP part, uses
**pointer** as a label to mark the position of remaining different part.

Yet the problem is that, **pointer** is a compat_caddr_t type, which may
be smaller than the relative structure at the same position. So during
wireless_send_event() tries to parse the wireless events payload, it may
trigger the memcpy() run-time destination buffer bounds checking when the
relative structure's data is copied to the position marked by **pointer**.

This patch solves it by introducing flexible-array field **ptr_bytes**,
to mark the position of the wireless events remaining part next to
LCP part. What's more, this patch also adds **ptr_len** variable in
wireless_send_event() to improve its maintainability.

Reported-and-tested-by: syzbot+473754e5af963cf014cf@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/00000000000070db2005e95a5984@google.com/
Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/wireless.h b/include/linux/wireless.h
index 2d1b545..e6e34d7 100644 (file)
--- a/include/linux/wireless.h
+++ b/include/linux/wireless.h
@@ -26,7 +26,15 @@ struct compat_iw_point {
 struct __compat_iw_event {
        __u16           len;                    /* Real length of this stuff */
        __u16           cmd;                    /* Wireless IOCTL */
-       compat_caddr_t  pointer;
+
+       union {
+               compat_caddr_t  pointer;
+
+               /* we need ptr_bytes to make memcpy() run-time destination
+                * buffer bounds checking happy, nothing special
+                */
+               DECLARE_FLEX_ARRAY(__u8, ptr_bytes);
+       };
 };
 #define IW_EV_COMPAT_LCP_LEN offsetof(struct __compat_iw_event, pointer)
 #define IW_EV_COMPAT_POINT_OFF offsetof(struct compat_iw_point, length)

diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
index 76a80a4..fe8765c 100644 (file)
--- a/net/wireless/wext-core.c
+++ b/net/wireless/wext-core.c
@@ -468,6 +468,7 @@ void wireless_send_event(struct net_device *        dev,
        struct __compat_iw_event *compat_event;
        struct compat_iw_point compat_wrqu;
        struct sk_buff *compskb;
+       int ptr_len;
 #endif
 
        /*
@@ -582,6 +583,9 @@ void wireless_send_event(struct net_device *        dev,
        nlmsg_end(skb, nlh);
 #ifdef CONFIG_COMPAT
        hdr_len = compat_event_type_size[descr->header_type];
+
+       /* ptr_len is remaining size in event header apart from LCP */
+       ptr_len = hdr_len - IW_EV_COMPAT_LCP_LEN;
        event_len = hdr_len + extra_len;
 
        compskb = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
@@ -612,16 +616,15 @@ void wireless_send_event(struct net_device *      dev,
        if (descr->header_type == IW_HEADER_TYPE_POINT) {
                compat_wrqu.length = wrqu->data.length;
                compat_wrqu.flags = wrqu->data.flags;
-               memcpy(&compat_event->pointer,
-                       ((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
-                       hdr_len - IW_EV_COMPAT_LCP_LEN);
+               memcpy(compat_event->ptr_bytes,
+                      ((char *)&compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
+                       ptr_len);
                if (extra_len)
-                       memcpy(((char *) compat_event) + hdr_len,
-                               extra, extra_len);
+                       memcpy(&compat_event->ptr_bytes[ptr_len],
+                              extra, extra_len);
        } else {
                /* extra_len must be zero, so no if (extra) needed */
-               memcpy(&compat_event->pointer, wrqu,
-                       hdr_len - IW_EV_COMPAT_LCP_LEN);
+               memcpy(compat_event->ptr_bytes, wrqu, ptr_len);
        }
 
        nlmsg_end(compskb, nlh);