https://bugs.kde.org/show_bug.cgi?id=424018
Bug ID: 424018
Summary: Valgrind crashes with --trace-syscalls=yes if syscalls
use PRINT %s with a non-dereferenceable string
Product: valgrind
Version: unspecified
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
As a quick example, in the memcheck/tests/x86-linux directory if I run
../../../vg-in-place --trace-syscalls=yes ./scalar < scalar.c
then I get
-----------------------------------------------------
11: __NR_execve 3s 1m
-----------------------------------------------------
SYSCALL[13743,1](4) ... [async] --> Success(0x8b)
SYSCALL[13743,1](11) --13743-- VALGRIND INTERNAL ERROR: Valgrind received a
signal 11 (SIGSEGV) - exiting
--13743-- si_code=1; Faulting address: 0x1; sp: 0x8288bb28
valgrind: the 'impossible' happened:
Killed by fatal signal
host stacktrace:
==13743== at 0x5801E368: myvprintf_str (m_debuglog.c:623)
==13743== by 0x5801EBAD: vgPlain_debugLog_vprintf (m_debuglog.c:1027)
==13743== by 0x58028850: vprintf_WRK (m_libcprint.c:647)
==13743== by 0x58028C11: vgPlain_printf (m_libcprint.c:671)
==13743== by 0x58070414: vgSysWrap_generic_sys_execve_before
(syswrap-generic.c:3152)
==13743== by 0x58014F49: vgPlain_client_syscall (syswrap-main.c:1914)
==13743== by 0x580123F8: handle_syscall (scheduler.c:1208)
==13743== by 0x58013A19: vgPlain_scheduler (scheduler.c:1526)
==13743== by 0x58076D03: run_a_thread_NORETURN (syswrap-linux.c:101)
The code in scalar.c is
// __NR_execve 11
GO(__NR_execve, "3s 1m");
SY(__NR_execve, x0 + 1, x0 + 1, x0); FAIL;
The execve signature is
int execve(const char *filename, char *const argv[],
char *const envp[]);
As the stacktrace says, this is handled in syswrap-generic.c
PRINT("sys_execve ( %#" FMT_REGWORD "x(%s), %#" FMT_REGWORD "x, %#"
FMT_REGWORD "x )", ARG1, (HChar*)(Addr)ARG1, ARG2, ARG3);
The problem is with the "(%s)" dereferencing (HChar*)(Addr)ARG1, which is 1.
I suggest adding a new function such as
const HChar* ML_(sanitize_string)(Addr ptr)
{
if (ML_(safe_to_deref)((const void *)ptr, 1)) {
return (const HChar*)pr;
} else {
return "invalid string";
}
}
and changing the PRINT to
PRINT("sys_execve ( %#" FMT_REGWORD "x(%s), %#" FMT_REGWORD "x, %#"
FMT_REGWORD "x )", ARG1, ML_(sanitize_sring)((Addr)ARG1), ARG2, ARG3);
I'm not providing a patch as there are many other similar examples.
It might also be possible to change VG_(printf) to handle non-dereferenceable
pointers. That would require fewer code changes at the expense of always
checking pointers.
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