Fix: getgrnam is not MT-Safe, use getgrnam_r

Running the test suite under a Yocto musl build resulted in musl
coredump due to double freeing.

We get the following backtraces:

0  a_crash () at ./arch/x86_64/atomic_arch.h:108
1  unmap_chunk (self=<optimized out>) at src/malloc/malloc.c:515
2  free (p=<optimized out>) at src/malloc/malloc.c:526
3  0x00007f46d9dc3849 in __getgrent_a (f=f@entry=0x7f46d9d1f7e0, gr=gr@entry=0x7f46d9e24460 <gr>, line=line@entry=0x7f46d9e26058 <line>, size=size@entry=0x7f46d92db550, mem=mem@entry=0x7f46d9e26050 <mem>, nmem=nmem@entry=0x7f46d92db558, res=0x7f46d92db548) at src/passwd/getgrent_a.c:45
4  0x00007f46d9dc2e6b in __getgr_a (name=0x487242 "tracing", gid=gid@entry=0, gr=gr@entry=0x7f46d9e24460 <gr>, buf=buf@entry=0x7f46d9e26058 <line>, size=size@entry=0x7f46d92db550, mem=mem@entry=0x7f46d9e26050 <mem>, nmem=0x7f46d92db558, res=0x7f46d92db548) at src/passwd/getgr_a.c:30
5  0x00007f46d9dc3733 in getgrnam (name=<optimized out>) at src/passwd/getgrent.c:37
6  0x0000000000460b29 in utils_get_group_id (name=<optimized out>) at ../../../lttng-tools-2.10.6/src/common/utils.c:1241
7  0x000000000044ee69 in thread_manage_health (data=<optimized out>) at ../../../../lttng-tools-2.10.6/src/bin/lttng-sessiond/main.c:4115
8  0x00007f46d9de1541 in start (p=<optimized out>) at src/thread/pthread_create.c:195
9  0x00007f46d9dee661 in __clone () at src/thread/x86_64/clone.s:22

From another run:

0  a_crash () at ./arch/x86_64/atomic_arch.h:108
1  unmap_chunk (self=<optimized out>) at src/malloc/malloc.c:515
2  free (p=<optimized out>) at src/malloc/malloc.c:526
3  0x00007f5abc210849 in __getgrent_a (f=f@entry=0x7f5abc2733e0, gr=gr@entry=0x7f5abc271460 <gr>, line=line@entry=0x7f5abc273058 <line>, size=size@entry=0x7f5abaef5510, mem=mem@entry=0x7f5abc273050 <mem>, nmem=nmem@entry=0x7f5abaef5518, res=0x7f5abaef5508) at src/passwd/getgrent_a.c:45
4  0x00007f5abc20fe6b in __getgr_a (name=0x487242 "tracing", gid=gid@entry=0, gr=gr@entry=0x7f5abc271460 <gr>, buf=buf@entry=0x7f5abc273058 <line>, size=size@entry=0x7f5abaef5510, mem=mem@entry=0x7f5abc273050 <mem>, nmem=0x7f5abaef5518, res=0x7f5abaef5508) at src/passwd/getgr_a.c:30
5  0x00007f5abc210733 in getgrnam (name=<optimized out>) at src/passwd/getgrent.c:37
6  0x0000000000460b29 in utils_get_group_id (name=<optimized out>) at ../../../lttng-tools-2.10.6/src/common/utils.c:1241
7  0x000000000042dee4 in notification_channel_socket_create () at ../../../../lttng-tools-2.10.6/src/bin/lttng-sessiond/notification-thread.c:238
8  init_thread_state (state=0x7f5abaef5560, handle=0x7f5abbf9be40) at ../../../../lttng-tools-2.10.6/src/bin/lttng-sessiond/notification-thread.c:375
9  thread_notification (data=0x7f5abbf9be40) at ../../../../lttng-tools-2.10.6/src/bin/lttng-sessiond/notification-thread.c:495
10 0x00007f5abc22e541 in start (p=<optimized out>) at src/thread/pthread_create.c:195
11 0x00007f5abc23b661 in __clone () at src/thread/x86_64/clone.s:22

The problem was easily reproducible (~6 crash on ~300 runs). A prototype fix
using mutex around the getgrnam yielded no crash in over 1000 runs. This
patch yielded the same results as the prototype fix.

Unfortunately we cannot rely on a mutex in liblttng-ctl since we cannot
enforce the locking for the application using the lib.

Use getgrnam_r instead.

The previous implementation of utils_get_group_id returned the gid of
the root group (0) on error/not found. lttng_check_tracing_group needs
to know if an error/not found occured, returning the root group is not
enough. We now return the gid via the passed parameter. The caller is
responsible for either defaulting to the root group or propagating the
error.

We also do not want to warn when used in liblttng-ctl context. We might
want to move the warning elsewhere in the future. For now, pass a bool
if we need to warn or not.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/src/bin/lttng-consumerd/health-consumerd.c b/src/bin/lttng-consumerd/health-consumerd.c
index 1e2f31e488b51cb3f42af09adb299ea7448afac2..15b71a1abc7cc68214972e56a0eb923e31098d78 100644 (file)
--- a/src/bin/lttng-consumerd/health-consumerd.c
+++ b/src/bin/lttng-consumerd/health-consumerd.c
@@ -184,8 +184,15 @@ void *thread_manage_health(void *data)
        is_root = !getuid();
        if (is_root) {
                /* lttng health client socket path permissions */
-               ret = chown(health_unix_sock_path, 0,
-                               utils_get_group_id(tracing_group_name));
+               gid_t gid;
+
+               ret = utils_get_group_id(tracing_group_name, true, &gid);
+               if (ret) {
+                       /* Default to root group. */
+                       gid = 0;
+               }
+
+               ret = chown(health_unix_sock_path, 0, gid);
                if (ret < 0) {
                        ERR("Unable to set group on %s", health_unix_sock_path);
                        PERROR("chown");

diff --git a/src/bin/lttng-relayd/health-relayd.c b/src/bin/lttng-relayd/health-relayd.c
index ba996621b0058ca62f94a7d1c4b001a5737b1b2e..9b4eefcd55f93e7ad6e9e5e018a398b76fc75f5a 100644 (file)
--- a/src/bin/lttng-relayd/health-relayd.c
+++ b/src/bin/lttng-relayd/health-relayd.c
@@ -105,8 +105,15 @@ static int create_lttng_rundir_with_perm(const char *rundir)
                int is_root = !getuid();
 
                if (is_root) {
-                       ret = chown(rundir, 0,
-                                       utils_get_group_id(tracing_group_name));
+                       gid_t gid;
+
+                       ret = utils_get_group_id(tracing_group_name, true, &gid);
+                       if (ret) {
+                               /* Default to root group. */
+                               gid = 0;
+                       }
+
+                       ret = chown(rundir, 0, gid);
                        if (ret < 0) {
                                ERR("Unable to set group on %s", rundir);
                                PERROR("chown");
@@ -256,8 +263,15 @@ void *thread_manage_health(void *data)
        is_root = !getuid();
        if (is_root) {
                /* lttng health client socket path permissions */
-               ret = chown(health_unix_sock_path, 0,
-                               utils_get_group_id(tracing_group_name));
+               gid_t gid;
+
+               ret = utils_get_group_id(tracing_group_name, true, &gid);
+               if (ret) {
+                       /* Default to root group. */
+                       gid = 0;
+               }
+
+               ret = chown(health_unix_sock_path, 0, gid);
                if (ret < 0) {
                        ERR("Unable to set group on %s", health_unix_sock_path);
                        PERROR("chown");

diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index fa6fa4830e468efc0180a88e1888434f67955a25..577936a89ff2d8f1e09aa68c14a4052f8581efe0 100644 (file)
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -4111,9 +4111,17 @@ static void *thread_manage_health(void *data)
        }
 
        if (is_root) {
+               gid_t gid;
+
                /* lttng health client socket path permissions */
+               ret = utils_get_group_id(config.tracing_group_name.value, true,
+                               &gid);
+               if (ret) {
+                       /* Default to root group. */
+                       gid = 0;
+               }
                ret = chown(config.health_unix_sock_path.value, 0,
-                               utils_get_group_id(config.tracing_group_name.value));
+                               gid);
                if (ret < 0) {
                        ERR("Unable to set group on %s", config.health_unix_sock_path.value);
                        PERROR("chown");
@@ -5238,7 +5246,11 @@ static int set_permissions(char *rundir)
        int ret;
        gid_t gid;
 
-       gid = utils_get_group_id(config.tracing_group_name.value);
+       ret = utils_get_group_id(config.tracing_group_name.value, true, &gid);
+       if (ret) {
+               /* Default to root group. */
+               gid = 0;
+       }
 
        /* Set lttng run dir */
        ret = chown(rundir, 0, gid);
@@ -5349,7 +5361,16 @@ static int set_consumer_sockets(struct consumer_data *consumer_data)
                goto error;
        }
        if (is_root) {
-               ret = chown(path, 0, utils_get_group_id(config.tracing_group_name.value));
+               gid_t gid;
+
+               ret = utils_get_group_id(config.tracing_group_name.value, true,
+                               &gid);
+               if (ret) {
+                       /* Default to root group. */
+                       gid = 0;
+               }
+
+               ret = chown(path, 0, gid);
                if (ret < 0) {
                        ERR("Unable to set group on %s", path);
                        PERROR("chown");

diff --git a/src/bin/lttng-sessiond/notification-thread.c b/src/bin/lttng-sessiond/notification-thread.c
index 92ac597fa00a58e7720f6710579df372c22cd6a6..9ee208bafc88140178f96bca5be6932b64d31622 100644 (file)
--- a/src/bin/lttng-sessiond/notification-thread.c
+++ b/src/bin/lttng-sessiond/notification-thread.c
@@ -235,8 +235,16 @@ int notification_channel_socket_create(void)
        }
 
        if (getuid() == 0) {
-               ret = chown(sock_path, 0,
-                               utils_get_group_id(config.tracing_group_name.value));
+               gid_t gid;
+
+               ret =  utils_get_group_id(config.tracing_group_name.value, true,
+                               &gid);
+               if (ret) {
+                       /* Default to root group. */
+                       gid = 0;
+               }
+
+               ret = chown(sock_path, 0, gid);
                if (ret) {
                        ERR("Failed to set the notification channel socket's group");
                        ret = -1;

diff --git a/src/common/utils.c b/src/common/utils.c
index c0bb031e9dc02f48d9cc5fdb425826fbe84907ba..8ac143cb20f3779a9112009c5ca6dc795de109e7 100644 (file)
--- a/src/common/utils.c
+++ b/src/common/utils.c
@@ -37,6 +37,7 @@
 #include <common/compat/getenv.h>
 #include <common/compat/string.h>
 #include <common/compat/dirent.h>
+#include <common/dynamic-buffer.h>
 #include <lttng/constant.h>
 
 #include "utils.h"
@@ -1231,24 +1232,77 @@ size_t utils_get_current_time_str(const char *format, char *dst, size_t len)
 }
 
 /*
- * Return the group ID matching name, else 0 if it cannot be found.
+ * Return 0 on success and set *gid to the group_ID matching the passed name.
+ * Else -1 if it cannot be found or an error occurred.
  */
 LTTNG_HIDDEN
-gid_t utils_get_group_id(const char *name)
+int utils_get_group_id(const char *name, bool warn, gid_t *gid)
 {
-       struct group *grp;
+       static volatile int warn_once;
+       int ret;
+       long sys_len;
+       size_t len;
+       struct group grp;
+       struct group *result;
+       struct lttng_dynamic_buffer buffer;
+
+       /* Get the system limit, if it exists. */
+       sys_len = sysconf(_SC_GETGR_R_SIZE_MAX);
+       if (sys_len == -1) {
+               len = 1024;
+       } else {
+               len = (size_t) sys_len;
+       }
+
+       lttng_dynamic_buffer_init(&buffer);
+       ret = lttng_dynamic_buffer_set_size(&buffer, len);
+       if (ret) {
+               ERR("Failed to allocate group info buffer");
+               ret = -1;
+               goto error;
+       }
 
-       grp = getgrnam(name);
-       if (!grp) {
-               static volatile int warn_once;
+       while ((ret = getgrnam_r(name, &grp, buffer.data, buffer.size, &result)) == ERANGE) {
+               const size_t new_len = 2 * buffer.size;
 
-               if (!warn_once) {
-                       WARN("No tracing group detected");
-                       warn_once = 1;
+               /* Buffer is not big enough, increase its size. */
+               if (new_len < buffer.size) {
+                       ERR("Group info buffer size overflow");
+                       ret = -1;
+                       goto error;
                }
-               return 0;
+
+               ret = lttng_dynamic_buffer_set_size(&buffer, new_len);
+               if (ret) {
+                       ERR("Failed to grow group info buffer to %zu bytes",
+                                       new_len);
+                       ret = -1;
+                       goto error;
+               }
+       }
+       if (ret) {
+               PERROR("Failed to get group file entry for group name \"%s\"",
+                               name);
+               ret = -1;
+               goto error;
+       }
+
+       /* Group not found. */
+       if (!result) {
+               ret = -1;
+               goto error;
        }
-       return grp->gr_gid;
+
+       *gid = result->gr_gid;
+       ret = 0;
+
+error:
+       if (ret && warn && !warn_once) {
+               WARN("No tracing group detected");
+               warn_once = 1;
+       }
+       lttng_dynamic_buffer_reset(&buffer);
+       return ret;
 }
 
 /*

diff --git a/src/common/utils.h b/src/common/utils.h
index 18f19ef1abd078bc19ac9f5aca21100e67d9e997..9c72431df3bc036fb6a6b0bc0cf48452ed93134a 100644 (file)
--- a/src/common/utils.h
+++ b/src/common/utils.h
@@ -22,6 +22,8 @@
 #include <unistd.h>
 #include <stdint.h>
 #include <getopt.h>
+#include <stdbool.h>
+#include <sys/types.h>
 
 #define KIBI_LOG2 10
 #define MEBI_LOG2 20
@@ -52,7 +54,7 @@ int utils_get_count_order_u64(uint64_t x);
 char *utils_get_home_dir(void);
 char *utils_get_user_home_dir(uid_t uid);
 size_t utils_get_current_time_str(const char *format, char *dst, size_t len);
-gid_t utils_get_group_id(const char *name);
+int utils_get_group_id(const char *name, bool warn, gid_t *gid);
 char *utils_generate_optstring(const struct option *long_options,
                size_t opt_count);
 int utils_create_lock_file(const char *filepath);

diff --git a/src/lib/lttng-ctl/lttng-ctl.c b/src/lib/lttng-ctl/lttng-ctl.c
index 2d84aad90238904440f377eae0d945f59c0ecb20..561b0bcfba4e39a76eee320968985d8f09a18ef5 100644 (file)
--- a/src/lib/lttng-ctl/lttng-ctl.c
+++ b/src/lib/lttng-ctl/lttng-ctl.c
@@ -208,15 +208,13 @@ end:
 LTTNG_HIDDEN
 int lttng_check_tracing_group(void)
 {
-       struct group *grp_tracing;      /* no free(). See getgrnam(3) */
-       gid_t *grp_list;
+       gid_t *grp_list, tracing_gid;
        int grp_list_size, grp_id, i;
        int ret = -1;
        const char *grp_name = tracing_group;
 
        /* Get GID of group 'tracing' */
-       grp_tracing = getgrnam(grp_name);
-       if (!grp_tracing) {
+       if (utils_get_group_id(grp_name, false, &tracing_gid)) {
                /* If grp_tracing is NULL, the group does not exist. */
                goto end;
        }
@@ -241,7 +239,7 @@ int lttng_check_tracing_group(void)
        }
 
        for (i = 0; i < grp_list_size; i++) {
-               if (grp_list[i] == grp_tracing->gr_gid) {
+               if (grp_list[i] == tracing_gid) {
                        ret = 1;
                        break;
                }