[lttng-dev] [PATCH lttng-tools] Fix: getgrnam is not MT-Safe, use getgrnam_r
Jonathan Rajotte-Julien
jonathan.rajotte-julien at efficios.com
Mon Apr 1 16:37:50 EDT 2019
Note if you want to backport this,
The health thread code was moved between master and 2.10.
I can send the patch if you need.
Cheers
On Mon, Apr 01, 2019 at 04:33:41PM -0400, Jonathan Rajotte wrote:
> 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 at entry=0x7f46d9d1f7e0, gr=gr at entry=0x7f46d9e24460 <gr>, line=line at entry=0x7f46d9e26058 <line>, size=size at entry=0x7f46d92db550, mem=mem at entry=0x7f46d9e26050 <mem>, nmem=nmem at entry=0x7f46d92db558, res=0x7f46d92db548) at src/passwd/getgrent_a.c:45
> 4 0x00007f46d9dc2e6b in __getgr_a (name=0x487242 "tracing", gid=gid at entry=0, gr=gr at entry=0x7f46d9e24460 <gr>, buf=buf at entry=0x7f46d9e26058 <line>, size=size at entry=0x7f46d92db550, mem=mem at 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 at entry=0x7f5abc2733e0, gr=gr at entry=0x7f5abc271460 <gr>, line=line at entry=0x7f5abc273058 <line>, size=size at entry=0x7f5abaef5510, mem=mem at entry=0x7f5abc273050 <mem>, nmem=nmem at entry=0x7f5abaef5518, res=0x7f5abaef5508) at src/passwd/getgrent_a.c:45
> 4 0x00007f5abc20fe6b in __getgr_a (name=0x487242 "tracing", gid=gid at entry=0, gr=gr at entry=0x7f5abc271460 <gr>, buf=buf at entry=0x7f5abc273058 <line>, size=size at entry=0x7f5abaef5510, mem=mem at 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 at efficios.com>
> ---
> src/bin/lttng-consumerd/health-consumerd.c | 10 ++-
> src/bin/lttng-relayd/health-relayd.c | 20 ++++--
> src/bin/lttng-sessiond/health.c | 10 ++-
> src/bin/lttng-sessiond/main.c | 14 +++-
> src/bin/lttng-sessiond/notification-thread.c | 10 ++-
> src/common/utils.c | 75 +++++++++++++++++---
> src/common/utils.h | 4 +-
> src/lib/lttng-ctl/lttng-ctl.c | 8 +--
> 8 files changed, 122 insertions(+), 29 deletions(-)
>
> diff --git a/src/bin/lttng-consumerd/health-consumerd.c b/src/bin/lttng-consumerd/health-consumerd.c
> index 1e2f31e48..6045401a4 100644
> --- a/src/bin/lttng-consumerd/health-consumerd.c
> +++ b/src/bin/lttng-consumerd/health-consumerd.c
> @@ -184,8 +184,14 @@ 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) {
> + gid = 0; /* Default to root group. */
> + }
> +
> + 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..962e88c47 100644
> --- a/src/bin/lttng-relayd/health-relayd.c
> +++ b/src/bin/lttng-relayd/health-relayd.c
> @@ -105,8 +105,14 @@ 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) {
> + gid = 0; /* Default to root group.*/
> + }
> +
> + ret = chown(rundir, 0, gid);
> if (ret < 0) {
> ERR("Unable to set group on %s", rundir);
> PERROR("chown");
> @@ -256,8 +262,14 @@ 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) {
> + gid = 0; /* Default to root group */
> + }
> +
> + 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..9e639837b 100644
> --- a/src/bin/lttng-sessiond/health.c
> +++ b/src/bin/lttng-sessiond/health.c
> @@ -95,8 +95,14 @@ 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) {
> + gid = 0; /* Default to root group. */
> + }
> +
> + 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..1cbd3c14c 100644
> --- a/src/bin/lttng-sessiond/main.c
> +++ b/src/bin/lttng-sessiond/main.c
> @@ -1023,7 +1023,10 @@ 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) {
> + gid = 0; /* Default to root group */
> + }
>
> /* Set lttng run dir */
> ret = chown(rundir, 0, gid);
> @@ -1134,7 +1137,14 @@ 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) {
> + gid = 0; /* Default to root group */
> + }
> +
> + 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..5a625eb3c 100644
> --- a/src/bin/lttng-sessiond/notification-thread.c
> +++ b/src/bin/lttng-sessiond/notification-thread.c
> @@ -239,8 +239,14 @@ 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) {
> + gid = 0; /* Default to root group. */
> + }
> +
> + 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 4c000e9b4..c79906a29 100644
> --- a/src/common/utils.c
> +++ b/src/common/utils.c
> @@ -1477,24 +1477,77 @@ 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;
>
> - grp = getgrnam(name);
> - if (!grp) {
> - static volatile int warn_once;
> + int ret;
> + long sys_len;
> + size_t len;
> + struct group grp;
> + struct group *result;
> + char *buffer = NULL;
>
> - if (!warn_once) {
> - WARN("No tracing group detected");
> - warn_once = 1;
> + /* 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;
> + }
> +
> + buffer = malloc(len);
> + if (!buffer) {
> + PERROR("getgrnam_r malloc");
> + ret = -1;
> + goto error;
> + }
> +
> + while ((ret = getgrnam_r(name, &grp, buffer, len, &result)) == ERANGE)
> + {
> + /* Buffer is not big enough, increase its size. */
> + size_t new_len = 2 * len;
> + char *new_buffer = NULL;
> + if (new_len < len) {
> + ERR("getgrnam_r buffer size overflow");
> + ret = -1;
> + goto error;
> + }
> + len = new_len;
> + new_buffer = realloc(buffer, len);
> + if (!new_buffer) {
> + PERROR("getgrnam_r realloc");
> + ret = -1;
> + goto error;
> }
> - return 0;
> + buffer = new_buffer;
> + }
> + if (ret != 0) {
> + PERROR("getgrnam_r");
> + ret = -1;
> + goto error;
> + }
> +
> + /* Group not found. */
> + if (!result) {
> + ret = -1;
> + goto error;
> + }
> +
> + *gid = result->gr_gid;
> + ret = 0;
> +
> +error:
> + free(buffer);
> + if (ret && warn && !warn_once) {
> + WARN("No tracing group detected");
> + warn_once = 1;
> }
> - return grp->gr_gid;
> + return ret;
> }
>
> /*
> diff --git a/src/common/utils.h b/src/common/utils.h
> index 9e3fa60cd..9dc447378 100644
> --- 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
> @@ -54,7 +56,7 @@ 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 165fef4dc..403aa092b 100644
> --- a/src/lib/lttng-ctl/lttng-ctl.c
> +++ b/src/lib/lttng-ctl/lttng-ctl.c
> @@ -241,15 +241,13 @@ 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;
> }
> @@ -274,7 +272,7 @@ 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;
> }
> --
> 2.17.1
>
--
Jonathan Rajotte-Julien
EfficiOS
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