Revision 79a8a642bf05cd0dced20621f6fef9d884124abd authored by Kees Cook on 08 February 2018, 01:44:38 UTC, committed by David S. Miller on 08 February 2018, 20:15:48 UTC
Most callers of put_cmsg() use a "sizeof(foo)" for the length argument.
Within put_cmsg(), a copy_to_user() call is made with a dynamic size, as a
result of the cmsg header calculations. This means that hardened usercopy
will examine the copy, even though it was technically a fixed size and
should be implicitly whitelisted. All the put_cmsg() calls being built
from values in skbuff_head_cache are coming out of the protocol-defined
"cb" field, so whitelist this field entirely instead of creating per-use
bounce buffers, for which there are concerns about performance.
Original report was:
Bad or missing usercopy whitelist? Kernel memory exposure attempt detected from SLAB object 'skbuff_head_cache' (offset 64, size 16)!
WARNING: CPU: 0 PID: 3663 at mm/usercopy.c:81 usercopy_warn+0xdb/0x100 mm/usercopy.c:76
...
__check_heap_object+0x89/0xc0 mm/slab.c:4426
check_heap_object mm/usercopy.c:236 [inline]
__check_object_size+0x272/0x530 mm/usercopy.c:259
check_object_size include/linux/thread_info.h:112 [inline]
check_copy_size include/linux/thread_info.h:143 [inline]
copy_to_user include/linux/uaccess.h:154 [inline]
put_cmsg+0x233/0x3f0 net/core/scm.c:242
sock_recv_errqueue+0x200/0x3e0 net/core/sock.c:2913
packet_recvmsg+0xb2e/0x17a0 net/packet/af_packet.c:3296
sock_recvmsg_nosec net/socket.c:803 [inline]
sock_recvmsg+0xc9/0x110 net/socket.c:810
___sys_recvmsg+0x2a4/0x640 net/socket.c:2179
__sys_recvmmsg+0x2a9/0xaf0 net/socket.c:2287
SYSC_recvmmsg net/socket.c:2368 [inline]
SyS_recvmmsg+0xc4/0x160 net/socket.c:2352
entry_SYSCALL_64_fastpath+0x29/0xa0
Reported-by: syzbot+e2d6cfb305e9f3911dea@syzkaller.appspotmail.com
Fixes: 6d07d1cd300f ("usercopy: Restrict non-usercopy caches to size 0")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 parent e728789
uledmon.c
// SPDX-License-Identifier: GPL-2.0
/*
* uledmon.c
*
* This program creates a new userspace LED class device and monitors it. A
* timestamp and brightness value is printed each time the brightness changes.
*
* Usage: uledmon <device-name>
*
* <device-name> is the name of the LED class device to be created. Pressing
* CTRL+C will exit.
*/
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <linux/uleds.h>
int main(int argc, char const *argv[])
{
struct uleds_user_dev uleds_dev;
int fd, ret;
int brightness;
struct timespec ts;
if (argc != 2) {
fprintf(stderr, "Requires <device-name> argument\n");
return 1;
}
strncpy(uleds_dev.name, argv[1], LED_MAX_NAME_SIZE);
uleds_dev.max_brightness = 100;
fd = open("/dev/uleds", O_RDWR);
if (fd == -1) {
perror("Failed to open /dev/uleds");
return 1;
}
ret = write(fd, &uleds_dev, sizeof(uleds_dev));
if (ret == -1) {
perror("Failed to write to /dev/uleds");
close(fd);
return 1;
}
while (1) {
ret = read(fd, &brightness, sizeof(brightness));
if (ret == -1) {
perror("Failed to read from /dev/uleds");
close(fd);
return 1;
}
clock_gettime(CLOCK_MONOTONIC, &ts);
printf("[%ld.%09ld] %u\n", ts.tv_sec, ts.tv_nsec, brightness);
}
close(fd);
return 0;
}
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