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Subject[PATCH] exec: allow core_pipe recursion check to look for a value of 1 rather than 0
Hey all-
So, about 6 months ago, I made a set of changes to how the
core-dump-to-a-pipe feature in the kernel works. We had reports of several
races, including some reports of apps bypassing our recursion check so that a
process that was forked as part of a core_pattern setup could infinitely crash
and refork until the system crashed.

We fixes those by improving our recursion checks. The new check
basically refuses to fork a process if its core limit is zero, which works well.

Unfortunately, I've been getting grief from maintainer of user space
programs that are inserted as the forked process of core_pattern. They contend
that in order for their programs (such as abrt and apport) to work, all the
running processes in a system must have their core limits set to a non-zero
value, to which I say 'yes'. I did this by design, and think thats the right
way to do things.

But I've been asked to ease this burden on user space enough times that
I thought I would take a look at it. The first suggestion was to make the
recursion check fail on a non-zero 'special' number, like one. That way the
core collector process could set its core size ulimit to 1, and enable the
kernel's recursion detection. This isn't a bad idea on the surface, but I don't
like it since its opt-in, in that if a program like abrt or apport has a bug and
fails to set such a core limit, we're left with a recursively crashing system
again.

So I've come up with this. What I've done is modify the
call_usermodehelper api such that an extra parameter is added, a function
pointer which will be called by the user helper task, after it forks, but before
it exec's the required process. This will give the caller the opportunity to
get a call back in the processes context, allowing it to do whatever it needs to
to the process in the kernel prior to exec-ing the user space code. In the case
of do_coredump, this callback is ues to set the core ulimit of the helper
process to 1. This elimnates the opt-in problem that I had above, as it allows
the ulimit for core sizes to be set to the value of 1, which is what the
recursion check looks for in do_coredump.

This patch has been tested successfully by some of the Abrt maintainers
in fedora, with good results. Patch applies to the latest -mm tree as of this
AM.

Neil

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Tested-by: Jiri Moskovcak <jmoskovc@redhat.com>
CC: Ingo Molnar <mingo@redhat.com>
CC: drbd-dev@lists.linbit.com
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Thomas Sailer <t.sailer@alumni.ethz.ch>
CC: Adam Belay <abelay@mit.edu>
CC: Greg Kroah-Hartman <gregkh@suse.de>
CC: Michal Januszewski <spock@gentoo.org>
CC: Al Viro <viro@zeniv.linux.org.uk>
CC: Neil Brown <neilb@suse.de>
CC: Mark Fasheh <mfasheh@suse.com>
CC: Paul Menage <menage@google.com>
CC: Stephen Hemminger <shemminger@linux-foundation.org>
CC: Kentaro Takeda <takedakn@nttdata.co.jp>

arch/x86/kernel/cpu/mcheck/mce.c | 2 +-
drivers/block/drbd/drbd_nl.c | 2 +-
drivers/macintosh/therm_pm72.c | 2 +-
drivers/macintosh/windfarm_core.c | 2 +-
drivers/net/hamradio/baycom_epp.c | 2 +-
drivers/pnp/pnpbios/core.c | 2 +-
drivers/staging/rtl8187se/r8180_core.c | 2 +-
drivers/video/uvesafb.c | 2 +-
fs/exec.c | 18 +++++++++++++++---
fs/nfs/cache_lib.c | 2 +-
fs/ocfs2/stackglue.c | 2 +-
include/linux/kmod.h | 16 ++++++++++------
kernel/cgroup.c | 2 +-
kernel/kmod.c | 17 +++++++++++++----
kernel/sys.c | 2 +-
lib/kobject_uevent.c | 2 +-
net/bridge/br_stp_if.c | 4 ++--
security/keys/request_key.c | 2 +-
security/tomoyo/common.c | 2 +-
19 files changed, 55 insertions(+), 30 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index a8aacd4..1f59e0d 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1164,7 +1164,7 @@ static void mce_start_timer(unsigned long data)

static void mce_do_trigger(struct work_struct *work)
{
- call_usermodehelper(mce_helper, mce_helper_argv, NULL, UMH_NO_WAIT);
+ call_usermodehelper(mce_helper, mce_helper_argv, NULL, NULL, UMH_NO_WAIT);
}

static DECLARE_WORK(mce_trigger_work, mce_do_trigger);
diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index 4e0726a..ae2719b 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -172,7 +172,7 @@ int drbd_khelper(struct drbd_conf *mdev, char *cmd)
dev_info(DEV, "helper command: %s %s %s\n", usermode_helper, cmd, mb);

drbd_bcast_ev_helper(mdev, cmd);
- ret = call_usermodehelper(usermode_helper, argv, envp, 1);
+ ret = call_usermodehelper(usermode_helper, argv, envp, NULL, 1);
if (ret)
dev_warn(DEV, "helper command: %s %s %s exit code %u (0x%x)\n",
usermode_helper, cmd, mb,
diff --git a/drivers/macintosh/therm_pm72.c b/drivers/macintosh/therm_pm72.c
index 454bc50..899f895 100644
--- a/drivers/macintosh/therm_pm72.c
+++ b/drivers/macintosh/therm_pm72.c
@@ -1763,7 +1763,7 @@ static int call_critical_overtemp(void)
NULL };

return call_usermodehelper(critical_overtemp_path,
- argv, envp, UMH_WAIT_EXEC);
+ argv, envp, NULL, UMH_WAIT_EXEC);
}


diff --git a/drivers/macintosh/windfarm_core.c b/drivers/macintosh/windfarm_core.c
index 075b4d9..640c856 100644
--- a/drivers/macintosh/windfarm_core.c
+++ b/drivers/macintosh/windfarm_core.c
@@ -81,7 +81,7 @@ int wf_critical_overtemp(void)
NULL };

return call_usermodehelper(critical_overtemp_path,
- argv, envp, UMH_WAIT_EXEC);
+ argv, envp, NULL, UMH_WAIT_EXEC);
}
EXPORT_SYMBOL_GPL(wf_critical_overtemp);

diff --git a/drivers/net/hamradio/baycom_epp.c b/drivers/net/hamradio/baycom_epp.c
index a3c0dc9..daa2097 100644
--- a/drivers/net/hamradio/baycom_epp.c
+++ b/drivers/net/hamradio/baycom_epp.c
@@ -320,7 +320,7 @@ static int eppconfig(struct baycom_state *bc)
sprintf(portarg, "%ld", bc->pdev->port->base);
printk(KERN_DEBUG "%s: %s -s -p %s -m %s\n", bc_drvname, eppconfig_path, portarg, modearg);

- return call_usermodehelper(eppconfig_path, argv, envp, UMH_WAIT_PROC);
+ return call_usermodehelper(eppconfig_path, argv, envp, NULL, UMH_WAIT_PROC);
}

/* ---------------------------------------------------------------------- */
diff --git a/drivers/pnp/pnpbios/core.c b/drivers/pnp/pnpbios/core.c
index cfe8685..00bb172 100644
--- a/drivers/pnp/pnpbios/core.c
+++ b/drivers/pnp/pnpbios/core.c
@@ -142,7 +142,7 @@ static int pnp_dock_event(int dock, struct pnp_docking_station_info *info)
info->location_id, info->serial, info->capabilities);
envp[i] = NULL;

- value = call_usermodehelper(argv [0], argv, envp, UMH_WAIT_EXEC);
+ value = call_usermodehelper(argv [0], argv, envp, NULL, UMH_WAIT_EXEC);
kfree(buf);
kfree(envp);
return 0;
diff --git a/drivers/staging/rtl8187se/r8180_core.c b/drivers/staging/rtl8187se/r8180_core.c
index e0f13ef..aaafc00 100644
--- a/drivers/staging/rtl8187se/r8180_core.c
+++ b/drivers/staging/rtl8187se/r8180_core.c
@@ -4287,7 +4287,7 @@ void GPIOChangeRFWorkItemCallBack(struct work_struct *work)
argv[0] = RadioPowerPath;
argv[2] = NULL;

- call_usermodehelper(RadioPowerPath,argv,envp,1);
+ call_usermodehelper(RadioPowerPath,argv,envp,NULL,1);
}
}
}
diff --git a/drivers/video/uvesafb.c b/drivers/video/uvesafb.c
index 54fbb29..188aea3 100644
--- a/drivers/video/uvesafb.c
+++ b/drivers/video/uvesafb.c
@@ -120,7 +120,7 @@ static int uvesafb_helper_start(void)
NULL,
};

- return call_usermodehelper(v86d_path, argv, envp, 1);
+ return call_usermodehelper(v86d_path, argv, envp, NULL, 1);
}

/*
diff --git a/fs/exec.c b/fs/exec.c
index 632b02e..3f2f829 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1755,6 +1755,18 @@ static void wait_for_dump_helpers(struct file *file)

}

+/*
+ * This is used as a helper to set up the task that execs
+ * our user space core collector application
+ * Its called in the context of the task thats going to
+ * exec itself to be the helper, so we can modify current here
+ */
+void core_pipe_setup(void)
+{
+ task_lock(current->group_leader);
+ current->signal->rlim[RLIMIT_CORE].rlim_cur = 1;
+ task_unlock(current->group_leader);
+}

void do_coredump(long signr, int exit_code, struct pt_regs *regs)
{
@@ -1836,7 +1848,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
goto fail_unlock;

if (ispipe) {
- if (cprm.limit == 0) {
+ if (cprm.limit == 1) {
/*
* Normally core limits are irrelevant to pipes, since
* we're not writing to the file system, but we use
@@ -1852,7 +1864,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
* core_pattern process dies.
*/
printk(KERN_WARNING
- "Process %d(%s) has RLIMIT_CORE set to 0\n",
+ "Process %d(%s) has RLIMIT_CORE set to 1\n",
task_tgid_vnr(current), current->comm);
printk(KERN_WARNING "Aborting core\n");
goto fail_unlock;
@@ -1877,7 +1889,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)

/* SIGPIPE can happen, but it's just never processed */
if (call_usermodehelper_pipe(helper_argv[0], helper_argv, NULL,
- &cprm.file)) {
+ &cprm.file, core_pipe_setup)) {
printk(KERN_INFO "Core dump to %s pipe failed\n",
corename);
goto fail_dropcount;
diff --git a/fs/nfs/cache_lib.c b/fs/nfs/cache_lib.c
index b4ffd01..73d79e9 100644
--- a/fs/nfs/cache_lib.c
+++ b/fs/nfs/cache_lib.c
@@ -46,7 +46,7 @@ int nfs_cache_upcall(struct cache_detail *cd, char *entry_name)

if (nfs_cache_getent_prog[0] == '\0')
goto out;
- ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
+ ret = call_usermodehelper(argv[0], argv, envp, NULL, UMH_WAIT_EXEC);
/*
* Disable the upcall mechanism if we're getting an ENOENT or
* EACCES error. The admin can re-enable it on the fly by using
diff --git a/fs/ocfs2/stackglue.c b/fs/ocfs2/stackglue.c
index f3df0ba..dddf780 100644
--- a/fs/ocfs2/stackglue.c
+++ b/fs/ocfs2/stackglue.c
@@ -407,7 +407,7 @@ static void ocfs2_leave_group(const char *group)
envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
envp[2] = NULL;

- ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);
+ ret = call_usermodehelper(argv[0], argv, envp, NULL, UMH_WAIT_PROC);
if (ret < 0) {
printk(KERN_ERR
"ocfs2: Error %d running user helper "
diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index 384ca8b..ca5e531 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -48,7 +48,9 @@ struct subprocess_info;

/* Allocate a subprocess_info structure */
struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
- char **envp, gfp_t gfp_mask);
+ char **envp,
+ void (*finit)(void),
+ gfp_t gfp_mask);

/* Set various pieces of state into the subprocess_info structure */
void call_usermodehelper_setkeys(struct subprocess_info *info,
@@ -72,12 +74,13 @@ int call_usermodehelper_exec(struct subprocess_info *info, enum umh_wait wait);
void call_usermodehelper_freeinfo(struct subprocess_info *info);

static inline int
-call_usermodehelper(char *path, char **argv, char **envp, enum umh_wait wait)
+call_usermodehelper(char *path, char **argv, char **envp,
+ void (*finit)(void), enum umh_wait wait)
{
struct subprocess_info *info;
gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;

- info = call_usermodehelper_setup(path, argv, envp, gfp_mask);
+ info = call_usermodehelper_setup(path, argv, envp, finit, gfp_mask);
if (info == NULL)
return -ENOMEM;
return call_usermodehelper_exec(info, wait);
@@ -85,12 +88,13 @@ call_usermodehelper(char *path, char **argv, char **envp, enum umh_wait wait)

static inline int
call_usermodehelper_keys(char *path, char **argv, char **envp,
- struct key *session_keyring, enum umh_wait wait)
+ struct key *session_keyring,
+ void (*finit)(void), enum umh_wait wait)
{
struct subprocess_info *info;
gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;

- info = call_usermodehelper_setup(path, argv, envp, gfp_mask);
+ info = call_usermodehelper_setup(path, argv, envp, finit, gfp_mask);
if (info == NULL)
return -ENOMEM;

@@ -102,7 +106,7 @@ extern void usermodehelper_init(void);

struct file;
extern int call_usermodehelper_pipe(char *path, char *argv[], char *envp[],
- struct file **filp);
+ struct file **filp, void (*finit)(void));

extern int usermodehelper_disable(void);
extern void usermodehelper_enable(void);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1fbcc74..2dcbd51 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3780,7 +3780,7 @@ static void cgroup_release_agent(struct work_struct *work)
* since the exec could involve hitting disk and hence
* be a slow process */
mutex_unlock(&cgroup_mutex);
- call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
+ call_usermodehelper(argv[0], argv, envp, NULL, UMH_WAIT_EXEC);
mutex_lock(&cgroup_mutex);
continue_free:
kfree(pathbuf);
diff --git a/kernel/kmod.c b/kernel/kmod.c
index bf0e231..c80db3c 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -35,6 +35,7 @@
#include <linux/resource.h>
#include <linux/notifier.h>
#include <linux/suspend.h>
+#include <linux/gfp.h>
#include <asm/uaccess.h>

#include <trace/events/module.h>
@@ -117,7 +118,7 @@ int __request_module(bool wait, const char *fmt, ...)
trace_module_request(module_name, wait, _RET_IP_);

ret = call_usermodehelper(modprobe_path, argv, envp,
- wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
+ NULL, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
atomic_dec(&kmod_concurrent);
return ret;
}
@@ -134,6 +135,7 @@ struct subprocess_info {
enum umh_wait wait;
int retval;
struct file *stdin;
+ void (*finit)(void);
void (*cleanup)(char **argv, char **envp);
};

@@ -184,6 +186,9 @@ static int ____call_usermodehelper(void *data)
*/
set_user_nice(current, 0);

+ if (sub_info->finit)
+ sub_info->finit();
+
retval = kernel_execve(sub_info->path, sub_info->argv, sub_info->envp);

/* Exec failed? */
@@ -365,7 +370,9 @@ static inline void helper_unlock(void) {}
* exec the process and free the structure.
*/
struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
- char **envp, gfp_t gfp_mask)
+ char **envp,
+ void (*finit)(void),
+ gfp_t gfp_mask)
{
struct subprocess_info *sub_info;
sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
@@ -381,6 +388,7 @@ struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
kfree(sub_info);
return NULL;
}
+ sub_info->finit = finit;

out:
return sub_info;
@@ -510,12 +518,13 @@ EXPORT_SYMBOL(call_usermodehelper_exec);
* lower-level call_usermodehelper_* functions.
*/
int call_usermodehelper_pipe(char *path, char **argv, char **envp,
- struct file **filp)
+ struct file **filp,
+ void (*finit)(void))
{
struct subprocess_info *sub_info;
int ret;

- sub_info = call_usermodehelper_setup(path, argv, envp, GFP_KERNEL);
+ sub_info = call_usermodehelper_setup(path, argv, envp, finit, GFP_KERNEL);
if (sub_info == NULL)
return -ENOMEM;

diff --git a/kernel/sys.c b/kernel/sys.c
index 26a6b73..0ad1306 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1629,7 +1629,7 @@ int orderly_poweroff(bool force)
goto out;
}

- info = call_usermodehelper_setup(argv[0], argv, envp, GFP_ATOMIC);
+ info = call_usermodehelper_setup(argv[0], argv, envp, NULL, GFP_ATOMIC);
if (info == NULL) {
argv_free(argv);
goto out;
diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index 920a3ca..df55126 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -258,7 +258,7 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
goto exit;

retval = call_usermodehelper(argv[0], argv,
- env->envp, UMH_WAIT_EXEC);
+ env->envp, NULL, UMH_WAIT_EXEC);
}

exit:
diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
index 9a52ac5..9d75e7d 100644
--- a/net/bridge/br_stp_if.c
+++ b/net/bridge/br_stp_if.c
@@ -123,7 +123,7 @@ static void br_stp_start(struct net_bridge *br)
char *argv[] = { BR_STP_PROG, br->dev->name, "start", NULL };
char *envp[] = { NULL };

- r = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC);
+ r = call_usermodehelper(BR_STP_PROG, argv, envp, NULL, UMH_WAIT_PROC);
if (r == 0) {
br->stp_enabled = BR_USER_STP;
printk(KERN_INFO "%s: userspace STP started\n", br->dev->name);
@@ -146,7 +146,7 @@ static void br_stp_stop(struct net_bridge *br)
char *envp[] = { NULL };

if (br->stp_enabled == BR_USER_STP) {
- r = call_usermodehelper(BR_STP_PROG, argv, envp, 1);
+ r = call_usermodehelper(BR_STP_PROG, argv, envp, NULL, 1);
printk(KERN_INFO "%s: userspace STP stopped, return code %d\n",
br->dev->name, r);

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 03fe63e..f929b69 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -139,7 +139,7 @@ static int call_sbin_request_key(struct key_construction *cons,

/* do it */
ret = call_usermodehelper_keys(argv[0], argv, envp, keyring,
- UMH_WAIT_PROC);
+ NULL, UMH_WAIT_PROC);
kdebug("usermode -> 0x%x", ret);
if (ret >= 0) {
/* ret is the exit/wait code */
diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
index e0d0354..4aeefd7 100644
--- a/security/tomoyo/common.c
+++ b/security/tomoyo/common.c
@@ -1882,7 +1882,7 @@ void tomoyo_load_policy(const char *filename)
envp[0] = "HOME=/";
envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
envp[2] = NULL;
- call_usermodehelper(argv[0], argv, envp, 1);
+ call_usermodehelper(argv[0], argv, envp, NULL, 1);

printk(KERN_INFO "TOMOYO: 2.2.0 2009/04/01\n");
printk(KERN_INFO "Mandatory Access Control activated.\n");

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