Re: net: socket: NULL ptr deref in sendmsg
From: Andrey Ryabinin
Date: Fri Jul 25 2014 - 11:29:49 EST
On 07/14/14 01:50, Sasha Levin wrote:
>
> I've tried debugging it, but I don't see a code path that could lead to that.
>
I finally found some time to take look at this and I've found where the problem is.
Sasha, I suppose there was no usual "Unable to handle NULL pointer deference" after KASAN's report, right?
This gave me a clue that address 0 is actually mapped and contains valid socket address structure in it.
I've managed to write a simple code (in attachment), which could easily reproduce this bug.
I've fixed it with the following patch, please take a look.
From: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
Subject: [PATCH] net: sendmsg: fix NULL pointer dereference
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 assigning m->msg_name to address if move_addr_to_kernel()
was successful.
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>
---
net/compat.c | 6 ++++--
net/core/iovec.c | 6 ++++--
2 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/net/compat.c b/net/compat.c
index 9a76eaf..eefd989 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -92,9 +92,11 @@ int verify_compat_iovec(struct msghdr *kern_msg, struct iovec *kern_iov,
kern_address);
if (err < 0)
return err;
- }
- if (kern_msg->msg_name)
+
kern_msg->msg_name = kern_address;
+ } else
+ if (kern_msg->msg_name)
+ kern_msg->msg_name = kern_address;
} else
kern_msg->msg_name = NULL;
diff --git a/net/core/iovec.c b/net/core/iovec.c
index 827dd6b..16bd954 100644
--- a/net/core/iovec.c
+++ b/net/core/iovec.c
@@ -47,9 +47,11 @@ int verify_iovec(struct msghdr *m, struct iovec *iov, struct sockaddr_storage *a
address);
if (err < 0)
return err;
- }
- if (m->msg_name)
+
m->msg_name = address;
+ } else
+ if (m->msg_name)
+ m->msg_name = address;
} else {
m->msg_name = NULL;
}
--
1.8.5.5
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#define PAYLOAD 1024
int main(void)
{
struct sockaddr_nl src_addr;
struct sockaddr_nl *dest_addr;
struct nlmsghdr *nlh = NULL;
struct iovec iov;
struct msghdr msg;
int fd;
memset(&msg, 0, sizeof(msg));
fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
if (fd < 0) {
perror("socket:");
return -1;
}
dest_addr = mmap(0, sizeof(*dest_addr), PROT_READ|PROT_WRITE,
MAP_FIXED|MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
if (dest_addr == MAP_FAILED) {
perror("mmap:");
close(fd);
return -1;
}
memset(&src_addr, 0, sizeof(src_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid();
bind(fd, (struct sockaddr*)&src_addr, sizeof(src_addr));
memset(dest_addr, 0, sizeof(*dest_addr));
dest_addr->nl_family = AF_NETLINK;
dest_addr->nl_pid = 0;
dest_addr->nl_groups = 0;
nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(PAYLOAD));
memset(nlh, 0, NLMSG_SPACE(PAYLOAD));
nlh->nlmsg_len = NLMSG_SPACE(PAYLOAD);
nlh->nlmsg_pid = getpid();
nlh->nlmsg_flags = 0;
strcpy(NLMSG_DATA(nlh), "Die kernel! Die!");
iov.iov_base = (void *)nlh;
iov.iov_len = nlh->nlmsg_len;
msg.msg_name = dest_addr;
msg.msg_namelen = sizeof(*dest_addr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
if (sendmsg(fd, &msg, 0) < 0) {
perror("sendmsg:");
close(fd);
return -1;
}
close(fd);
return 0;
}