On Mon, Sep 26, 2022 at 11:09:06PM +0800, Hawkins Jiawei wrote: > Syzkaller reports refcount bug as follows: "buffer overflow false positive" instead of "refcount bug" > ------------[ 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@xxxxxxxxxxxxxxxxxxxxxxxxx > Link: https://lore.kernel.org/all/00000000000070db2005e95a5984@xxxxxxxxxx/ > Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx> > Signed-off-by: Hawkins Jiawei <yin31149@xxxxxxxxx> Thanks for spinning this and getting it tested! Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -- Kees Cook
