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 <han...@stressinduktion.org>
Cc: Eric Dumazet <eduma...@google.com>
Cc: <sta...@vger.kernel.org>
Reported-by: Sasha Levin <sasha.le...@oracle.com>
Signed-off-by: Andrey Ryabinin <a.ryabi...@samsung.com>
---
net/compat.c | 9 +++++----
net/core/iovec.c | 6 +++---
2 files changed, 8 insertions(+), 7 deletions(-)
diff --git a/net/compat.c b/net/compat.c
index 9a76eaf..bc8aeef 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -85,7 +85,7 @@ int verify_compat_iovec(struct msghdr *kern_msg, struct iovec
*kern_iov,
{
int tot_len;
- if (kern_msg->msg_namelen) {
+ if (kern_msg->msg_name && kern_msg->msg_namelen) {
if (mode == VERIFY_READ) {
int err = move_addr_to_kernel(kern_msg->msg_name,
kern_msg->msg_namelen,
@@ -93,10 +93,11 @@ int verify_compat_iovec(struct msghdr *kern_msg, struct
iovec *kern_iov,
if (err < 0)
return err;
}
- if (kern_msg->msg_name)
- kern_msg->msg_name = kern_address;
- } else
+ kern_msg->msg_name = kern_address;
+ } else {
kern_msg->msg_name = NULL;
+ kern_msg->msg_namelen = 0;
+ }
tot_len = iov_from_user_compat_to_kern(kern_iov,
(struct compat_iovec __user
*)kern_msg->msg_iov,
diff --git a/net/core/iovec.c b/net/core/iovec.c
index 827dd6b..e1ec45a 100644
--- a/net/core/iovec.c
+++ b/net/core/iovec.c
@@ -39,7 +39,7 @@ int verify_iovec(struct msghdr *m, struct iovec *iov, struct
sockaddr_storage *a
{
int size, ct, err;
- if (m->msg_namelen) {
+ if (m->msg_name && m->msg_namelen) {
if (mode == VERIFY_READ) {
void __user *namep;
namep = (void __user __force *) m->msg_name;
@@ -48,10 +48,10 @@ int verify_iovec(struct msghdr *m, struct iovec *iov,
struct sockaddr_storage *a
if (err < 0)
return err;
}
- if (m->msg_name)
- m->msg_name = address;
+ m->msg_name = address;
} else {
m->msg_name = NULL;
+ m->msg_namelen = 0;
}
size = m->msg_iovlen * sizeof(struct iovec);
--
1.8.5.5
--
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