fix 319235 --db-attach=yes is broken with Yama ptrace scoping enabled
On Ubuntu systems, ptrace_scoping could forbid a process to ptrace another.
This ptrace scoping was already handled for vgdb by using SET_PTRACER
(the valgrind process must be ptraced by vgdb when it is blocked
in a syscall).
set_ptracer is however also needed when the old mechanism --db-attach=yes
is used.
The following changes are done:
* make the set_ptracer logic callable outside gdbserver
* make set_ptracer less restrictive (i.e. allow all
processes of the user to ptrace). This removes a limitation for vgdb.
* call the set_ptracer in the child launched for --db-attach=yes
* cleaned up the ptrace scope restriction message and doc as vgdb
is now working properly by default, even with ptrace_scope enabled.
git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13384 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/NEWS b/NEWS
index 7de23c4..e4f6768 100644
--- a/NEWS
+++ b/NEWS
@@ -222,6 +222,7 @@
315959 [390] valgrind man page has bogus SGCHECK (and no BBV) OPTIONS section
316144 [390] valgrind.1 manpage contains unknown ??? strings for some core option references
316145 [390] callgrind command line options in manpage reference (unknown) callgrind manual
+319235 [390] --db-attach=yes is broken with Yama ptrace scoping enabled
n-i-bz [390] report error for vgdb snapshot requested before execution
n-i-bz [390] Some wrong command line options could be ignored
n-i-bz [390] same as 303624 (fixed in 3.8.0), but for x86 android
diff --git a/coregrind/m_debugger.c b/coregrind/m_debugger.c
index e53094b..1c967ef 100644
--- a/coregrind/m_debugger.c
+++ b/coregrind/m_debugger.c
@@ -35,6 +35,7 @@
#include "pub_core_xarray.h"
#include "pub_core_clientstate.h"
#include "pub_core_debugger.h"
+#include "pub_core_gdbserver.h"
#include "pub_core_libcbase.h"
#include "pub_core_libcprint.h"
#include "pub_core_libcproc.h"
@@ -363,6 +364,7 @@
if (pid == 0) {
/* child */
+ VG_(set_ptracer)();
rc = VG_(ptrace)(VKI_PTRACE_TRACEME, 0, NULL, NULL);
vg_assert(rc == 0);
rc = VG_(kill)(VG_(getpid)(), VKI_SIGSTOP);
diff --git a/coregrind/m_gdbserver/remote-utils.c b/coregrind/m_gdbserver/remote-utils.c
index 8a9c969..59a698e 100644
--- a/coregrind/m_gdbserver/remote-utils.c
+++ b/coregrind/m_gdbserver/remote-utils.c
@@ -105,12 +105,7 @@
return 0; // all is ok.
}
-/* On systems that defines PR_SET_PTRACER, verify if ptrace_scope is
- is permissive enough for vgdb. Otherwise, call set_ptracer.
- This is especially aimed at Ubuntu >= 10.10 which has added
- the ptrace_scope context. */
-static
-void set_ptracer(void)
+void VG_(set_ptracer)(void)
{
#ifdef PR_SET_PTRACER
SysRes o;
@@ -132,11 +127,16 @@
dlog(1, "ptrace_scope %c\n", ptrace_scope);
if (ptrace_scope != '0') {
/* insufficient default ptrace_scope.
- Indicate to the kernel that we accept to be
- ptraced by our vgdb. */
- ret = VG_(prctl) (PR_SET_PTRACER, shared->vgdb_pid, 0, 0, 0);
- dlog(1, "set_ptracer to vgdb_pid %d result %d\n",
- shared->vgdb_pid, ret);
+ Indicate to the kernel that we accept to be ptraced. */
+#ifdef PR_SET_PTRACER_ANY
+ ret = VG_(prctl) (PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0);
+ dlog(1, "set_ptracer to PR_SET_PTRACER_ANY result %d\n", ret);
+#else
+ ret = VG_(prctl) (PR_SET_PTRACER, 1, 0, 0, 0);
+ dlog(1, "set_ptracer to 1 result %d\n", ret);
+#endif
+ if (ret)
+ VG_(umsg)("error calling PR_SET_PTRACER, vgdb might block\n");
}
} else {
dlog(0, "Could not read the ptrace_scope setting from %s\n",
@@ -181,7 +181,6 @@
be reasonably sure someone is reading on the other
side of the fifo. */
if (!vgdb_state_looks_bad("bad?@ensure_write_remote_desc")) {
- set_ptracer();
write_remote_desc = open_fifo ("write", to_gdb, VKI_O_WRONLY);
}
}
@@ -293,7 +292,7 @@
if (!mknod_done) {
mknod_done++;
-
+ VG_(set_ptracer)();
/*
* Unlink just in case a previous process with the same PID had been
* killed and hence Valgrind hasn't had the chance yet to remove these.
diff --git a/coregrind/pub_core_gdbserver.h b/coregrind/pub_core_gdbserver.h
index f4286c3..9cb06c9 100644
--- a/coregrind/pub_core_gdbserver.h
+++ b/coregrind/pub_core_gdbserver.h
@@ -53,6 +53,12 @@
// gdbserver is then stopped (using VG_(gdbserver) (0))
void VG_(gdbserver_exit) (ThreadId tid, VgSchedReturnCode tids_schedretcode);
+/* On systems that defines PR_SET_PTRACER, verify if ptrace_scope is
+ is permissive enough for vgdb or --db-attach=yes.
+ Otherwise, call set_ptracer.
+ This is especially aimed at Ubuntu >= 10.10 which has added
+ the ptrace_scope context. */
+void VG_(set_ptracer)(void);
/* Called by low level to insert or remove a break or watch point.
Break or watch point implementation is done using help from the tool.
diff --git a/coregrind/vgdb.c b/coregrind/vgdb.c
index fed0d92..dc3beda 100644
--- a/coregrind/vgdb.c
+++ b/coregrind/vgdb.c
@@ -101,14 +101,12 @@
#if defined(PTRACEINVOKER)
#include <sys/user.h>
#if defined(VGO_linux)
-# include <sys/prctl.h>
# include <linux/ptrace.h>
#endif
#endif
-// Outputs information for the user about ptrace_scope protection
-// or ptrace not working.
+// Outputs information for the user about ptrace not working.
static void ptrace_restrictions_msg(void);
static int debuglevel;
@@ -869,11 +867,7 @@
// address pushed on the stack should ensure this is detected.
/* Not yet attached. If problem, vgdb can abort,
- no cleanup needed.
-
- On Ubuntu>= 10.10, a /proc setting can disable ptrace.
- So, Valgrind has to SET_PTRACER this vgdb. Once this
- is done, this vgdb can ptrace the valgrind process. */
+ no cleanup needed. */
DEBUG(1, "attach to 'main' pid %d\n", pid);
if (!attach(pid, "attach main pid")) {
@@ -2049,27 +2043,6 @@
static
void ptrace_restrictions_msg(void)
{
-# ifdef PR_SET_PTRACER
- const char *ptrace_scope_setting_file = "/proc/sys/kernel/yama/ptrace_scope";
- int fd = -1;
- char ptrace_scope = 'X';
- fd = open (ptrace_scope_setting_file, O_RDONLY, 0);
- if (fd >= 0 && (read (fd, &ptrace_scope, 1) == 1) && (ptrace_scope != '0')) {
- fprintf (stderr,
- "Note: your kernel restricts ptrace invoker using %s\n"
- "vgdb will only be able to attach to a Valgrind process\n"
- "blocked in a system call *after* an initial successful attach\n",
- ptrace_scope_setting_file);
- } else if (ptrace_scope == 'X') {
- DEBUG (1,
- "PR_SET_PTRACER defined"
- " but could not determine ptrace scope from %s\n",
- ptrace_scope_setting_file);
- }
- if (fd >= 0)
- close (fd);
-# endif
-
# ifndef PTRACEINVOKER
fprintf(stderr,
"Note: ptrace invoker not implemented\n"
diff --git a/docs/xml/manual-core-adv.xml b/docs/xml/manual-core-adv.xml
index ff17351..870996f 100644
--- a/docs/xml/manual-core-adv.xml
+++ b/docs/xml/manual-core-adv.xml
@@ -995,7 +995,8 @@
<para>Connecting to or interrupting a Valgrind process blocked in
a system call requires the "ptrace" system call to be usable.
- This may be disabled in your kernel for security reasons.</para>
+ This may be disabled in your kernel for security reasons.
+ </para>
<para>When running your program, Valgrind's scheduler
periodically checks whether there is any work to be handled by
@@ -1043,24 +1044,9 @@
<para>Ubuntu versions 10.10 and later may restrict the scope of
ptrace to the children of the process calling ptrace. As the
Valgrind process is not a child of vgdb, such restricted scoping
- causes the ptrace calls to fail. To avoid that, when Valgrind
- gdbserver receives the first packet from a vgdb, it calls
- <computeroutput>prctl(PR_SET_PTRACER, vgdb_pid, 0, 0,
- 0)</computeroutput> to ensure vgdb can reliably use ptrace.
- Once <computeroutput>vgdb_pid</computeroutput> has been marked as
- a ptracer, vgdb can then properly force the invocation of
- Valgrind gdbserver when needed. To ensure the vgdb is set as a
- ptracer before the Valgrind process gets blocked in a system
- call, connect your GDB to the Valgrind gdbserver at startup by
- passing <option>--vgdb-error=0</option> to Valgrind.</para>
-
- <para>Note that
- this "set ptracer" technique does not solve the problem in the
- case where a standalone vgdb process wants to connect to the
- gdbserver, since the first command to be sent by a standalone
- vgdb must wake up the Valgrind process before Valgrind gdbserver
- will mark vgdb as a ptracer.
- </para>
+ causes the ptrace calls to fail. To avoid that, Valgrind will
+ automatically allow all processes belonging to the same userid to
+ "ptrace" a Valgrind process, by using PR_SET_PTRACER.</para>
<para>Unblocking processes blocked in system calls is not
currently implemented on Mac OS X and Android. So you cannot
diff --git a/gdbserver_tests/make_local_links b/gdbserver_tests/make_local_links
index 8e50093..73a2f00 100755
--- a/gdbserver_tests/make_local_links
+++ b/gdbserver_tests/make_local_links
@@ -99,8 +99,7 @@
# if ptrace not implemented in vgdb or OS restricts the initial attach,
# some tests would block for a loooonnnng time.
if gdbserver_tests/vgdb --help 2>&1 |
- grep -e 'ptrace invoker not implemented' \
- -e 'kernel restricts ptrace invoker' > /dev/null
+ grep -e 'ptrace invoker not implemented' > /dev/null
then
rm -f gdbserver_tests/vgdb.ptraceinvoker
else
