On Sa, 2014-07-26 at 21:26 +0400, Andrey Ryabinin wrote: > Sasha's report: > > While fuzzing with trinity inside a KVM tools guest running the latest -next > > kernel with the KASAN patchset, I've stumbled on the following spew: > > > > [ 4448.949424] ================================================================== > > [ 4448.951737] AddressSanitizer: user-memory-access on address 0 > > [ 4448.952988] Read of size 2 by thread T19638: > > [ 4448.954510] CPU: 28 PID: 19638 Comm: trinity-c76 Not tainted 3.16.0-rc4-next-20140711-sasha-00046-g07d3099-dirty #813 > > [ 4448.956823] ffff88046d86ca40 0000000000000000 ffff880082f37e78 ffff880082f37a40 > > [ 4448.958233] ffffffffb6e47068 ffff880082f37a68 ffff880082f37a58 ffffffffb242708d > > [ 4448.959552] 0000000000000000 ffff880082f37a88 ffffffffb24255b1 0000000000000000 > > [ 4448.961266] Call Trace: > > [ 4448.963158] dump_stack (lib/dump_stack.c:52) > > [ 4448.964244] kasan_report_user_access (mm/kasan/report.c:184) > > [ 4448.965507] __asan_load2 (mm/kasan/kasan.c:352) > > [ 4448.966482] ? netlink_sendmsg (net/netlink/af_netlink.c:2339) > > [ 4448.967541] netlink_sendmsg (net/netlink/af_netlink.c:2339) > > [ 4448.968537] ? get_parent_ip (kernel/sched/core.c:2555) > > [ 4448.970103] sock_sendmsg (net/socket.c:654) > > [ 4448.971584] ? might_fault (mm/memory.c:3741) > > [ 4448.972526] ? might_fault (./arch/x86/include/asm/current.h:14 mm/memory.c:3740) > > [ 4448.973596] ? verify_iovec (net/core/iovec.c:64) > > [ 4448.974522] ___sys_sendmsg (net/socket.c:2096) > > [ 4448.975797] ? put_lock_stats.isra.13 (./arch/x86/include/asm/preempt.h:98 kernel/locking/lockdep.c:254) > > [ 4448.977030] ? lock_release_holdtime (kernel/locking/lockdep.c:273) > > [ 4448.978197] ? lock_release_non_nested (kernel/locking/lockdep.c:3434 (discriminator 1)) > > [ 4448.979346] ? check_chain_key (kernel/locking/lockdep.c:2188) > > [ 4448.980535] __sys_sendmmsg (net/socket.c:2181) > > [ 4448.981592] ? trace_hardirqs_on_caller (kernel/locking/lockdep.c:2600) > > [ 4448.982773] ? trace_hardirqs_on (kernel/locking/lockdep.c:2607) > > [ 4448.984458] ? syscall_trace_enter (arch/x86/kernel/ptrace.c:1500 (discriminator 2)) > > [ 4448.985621] ? trace_hardirqs_on_caller (kernel/locking/lockdep.c:2600) > > [ 4448.986754] SyS_sendmmsg (net/socket.c:2201) > > [ 4448.987708] tracesys (arch/x86/kernel/entry_64.S:542) > > [ 4448.988929] ================================================================== > > This reports means that we've come to netlink_sendmsg() with msg->msg_name == NULL and msg->msg_namelen > 0. > > After this report there was no usual "Unable to handle kernel NULL pointer dereference" > and this gave me a clue that address 0 is mapped and contains valid socket address structure in it. > > This bug was introduced in f3d3342602f8bcbf37d7c46641cb9bca7618eb1c > (net: rework recvmsg handler msg_name and msg_namelen logic). > Commit message states that: > "Set msg->msg_name = NULL if user specified a NULL in msg_name but had a > non-null msg_namelen in verify_iovec/verify_compat_iovec. This doesn't > affect sendto as it would bail out earlier while trying to copy-in the > address." > But in fact this affects sendto when address 0 is mapped and contains > socket address structure in it. In such case copy-in address will succeed, > verify_iovec() function will successfully exit with msg->msg_namelen > 0 > and msg->msg_name == NULL. > > This patch fixes it by setting msg_namelen to 0 if msg_name == NULL. > > Cc: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx> > Cc: Eric Dumazet <edumazet@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx> > Signed-off-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> Acked-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx> Thank you! -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html