From 28ab59d0baef178a8629ec9fb517ba75efb46ea8 Mon Sep 17 00:00:00 2001 From: Jonathan Rajotte Date: Mon, 1 Apr 2019 16:33:41 -0400 Subject: [PATCH] Fix: getgrnam is not MT-Safe, use getgrnam_r MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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=) at src/malloc/malloc.c:515 2 free (p=) at src/malloc/malloc.c:526 3 0x00007f46d9dc3849 in __getgrent_a (f=f@entry=0x7f46d9d1f7e0, gr=gr@entry=0x7f46d9e24460 , line=line@entry=0x7f46d9e26058 , size=size@entry=0x7f46d92db550, mem=mem@entry=0x7f46d9e26050 , 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 , buf=buf@entry=0x7f46d9e26058 , size=size@entry=0x7f46d92db550, mem=mem@entry=0x7f46d9e26050 , nmem=0x7f46d92db558, res=0x7f46d92db548) at src/passwd/getgr_a.c:30 5 0x00007f46d9dc3733 in getgrnam (name=) at src/passwd/getgrent.c:37 6 0x0000000000460b29 in utils_get_group_id (name=) at ../../../lttng-tools-2.10.6/src/common/utils.c:1241 7 0x000000000044ee69 in thread_manage_health (data=) at ../../../../lttng-tools-2.10.6/src/bin/lttng-sessiond/main.c:4115 8 0x00007f46d9de1541 in start (p=) 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=) at src/malloc/malloc.c:515 2 free (p=) at src/malloc/malloc.c:526 3 0x00007f5abc210849 in __getgrent_a (f=f@entry=0x7f5abc2733e0, gr=gr@entry=0x7f5abc271460 , line=line@entry=0x7f5abc273058 , size=size@entry=0x7f5abaef5510, mem=mem@entry=0x7f5abc273050 , 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 , buf=buf@entry=0x7f5abc273058 , size=size@entry=0x7f5abaef5510, mem=mem@entry=0x7f5abc273050 , nmem=0x7f5abaef5518, res=0x7f5abaef5508) at src/passwd/getgr_a.c:30 5 0x00007f5abc210733 in getgrnam (name=) at src/passwd/getgrent.c:37 6 0x0000000000460b29 in utils_get_group_id (name=) 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=) 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 Signed-off-by: Jérémie Galarneau --- src/bin/lttng-consumerd/health-consumerd.c | 11 ++- src/bin/lttng-relayd/health-relayd.c | 22 ++++-- src/bin/lttng-sessiond/health.c | 11 ++- src/bin/lttng-sessiond/main.c | 17 ++++- src/bin/lttng-sessiond/notification-thread.c | 12 +++- src/common/utils.c | 76 +++++++++++++++++--- src/common/utils.h | 4 +- src/lib/lttng-ctl/lttng-ctl.c | 8 +-- 8 files changed, 132 insertions(+), 29 deletions(-) diff --git a/src/bin/lttng-consumerd/health-consumerd.c b/src/bin/lttng-consumerd/health-consumerd.c index 1e2f31e48..15b71a1ab 100644 --- 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 ba996621b..9b4eefcd5 100644 --- 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/health.c b/src/bin/lttng-sessiond/health.c index 921b45261..9474a8560 100644 --- a/src/bin/lttng-sessiond/health.c +++ b/src/bin/lttng-sessiond/health.c @@ -95,8 +95,15 @@ static void *thread_manage_health(void *data) if (is_root) { /* lttng health client socket path permissions */ - ret = chown(config.health_unix_sock_path.value, 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(config.health_unix_sock_path.value, 0, gid); if (ret < 0) { ERR("Unable to set group on %s", config.health_unix_sock_path.value); PERROR("chown"); diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c index 24855b976..57324820b 100644 --- a/src/bin/lttng-sessiond/main.c +++ b/src/bin/lttng-sessiond/main.c @@ -1023,7 +1023,11 @@ 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); @@ -1134,7 +1138,16 @@ 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 b42b282e1..7998f7e21 100644 --- a/src/bin/lttng-sessiond/notification-thread.c +++ b/src/bin/lttng-sessiond/notification-thread.c @@ -239,8 +239,16 @@ 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 5be67c11f..aada37fe7 100644 --- a/src/common/utils.c +++ b/src/common/utils.c @@ -39,6 +39,7 @@ #include #include #include +#include #include #include "utils.h" @@ -1374,24 +1375,77 @@ 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; + } + + 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; } - return 0; } - return grp->gr_gid; + 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; + } + + *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 f372bf464..5f95d4aab 100644 --- a/src/common/utils.h +++ b/src/common/utils.h @@ -22,6 +22,8 @@ #include #include #include +#include +#include #include @@ -56,7 +58,7 @@ 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 bbd9e8575..bbff088e0 100644 --- a/src/lib/lttng-ctl/lttng-ctl.c +++ b/src/lib/lttng-ctl/lttng-ctl.c @@ -243,15 +243,13 @@ 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; } @@ -276,7 +274,7 @@ 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; } -- 2.34.1