ustfork: Fix possible race conditions

[lttng-ust.git] / src / lib / lttng-ust-fork / ustfork.c

diff --git a/src/lib/lttng-ust-fork/ustfork.c b/src/lib/lttng-ust-fork/ustfork.c
index 321ffc30c0fd993d7be43a62fa9063fbe3a2e5ca..9508cc7520eaeb23145814c9976cd24b6501a2a3 100644 (file)
--- a/src/lib/lttng-ust-fork/ustfork.c
+++ b/src/lib/lttng-ust-fork/ustfork.c
@@ -18,25 +18,30 @@
 
 #include <lttng/ust-fork.h>
 
+#include <urcu/uatomic.h>
+
 pid_t fork(void)
 {
        static pid_t (*plibc_func)(void) = NULL;
+       pid_t (*func)(void);
        sigset_t sigset;
        pid_t retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "fork");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "fork");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"fork\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        lttng_ust_before_fork(&sigset);
        /* Do the real fork */
-       retval = plibc_func();
+       retval = func();
        saved_errno = errno;
        if (retval == 0) {
                /* child */
@@ -51,22 +56,25 @@ pid_t fork(void)
 int daemon(int nochdir, int noclose)
 {
        static int (*plibc_func)(int nochdir, int noclose) = NULL;
+       int (*func)(int nochdir, int noclose);
        sigset_t sigset;
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "daemon");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "daemon");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"daemon\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        lttng_ust_before_fork(&sigset);
        /* Do the real daemon call */
-       retval = plibc_func(nochdir, noclose);
+       retval = func(nochdir, noclose);
        saved_errno = errno;
        if (retval == 0) {
                /* child, parent called _exit() directly */
@@ -82,20 +90,23 @@ int daemon(int nochdir, int noclose)
 int setuid(uid_t uid)
 {
        static int (*plibc_func)(uid_t uid) = NULL;
+       int (*func)(uid_t uid);
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "setuid");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "setuid");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"setuid\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        /* Do the real setuid */
-       retval = plibc_func(uid);
+       retval = func(uid);
        saved_errno = errno;
 
        lttng_ust_after_setuid();
@@ -107,20 +118,23 @@ int setuid(uid_t uid)
 int setgid(gid_t gid)
 {
        static int (*plibc_func)(gid_t gid) = NULL;
+       int (*func)(gid_t gid);
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "setgid");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "setgid");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"setgid\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        /* Do the real setgid */
-       retval = plibc_func(gid);
+       retval = func(gid);
        saved_errno = errno;
 
        lttng_ust_after_setgid();
@@ -132,20 +146,23 @@ int setgid(gid_t gid)
 int seteuid(uid_t euid)
 {
        static int (*plibc_func)(uid_t euid) = NULL;
+       int (*func)(uid_t euid);
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "seteuid");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "seteuid");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"seteuid\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        /* Do the real seteuid */
-       retval = plibc_func(euid);
+       retval = func(euid);
        saved_errno = errno;
 
        lttng_ust_after_seteuid();
@@ -157,20 +174,23 @@ int seteuid(uid_t euid)
 int setegid(gid_t egid)
 {
        static int (*plibc_func)(gid_t egid) = NULL;
+       int (*func)(gid_t egid);
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "setegid");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "setegid");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"setegid\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        /* Do the real setegid */
-       retval = plibc_func(egid);
+       retval = func(egid);
        saved_errno = errno;
 
        lttng_ust_after_setegid();
@@ -182,20 +202,23 @@ int setegid(gid_t egid)
 int setreuid(uid_t ruid, uid_t euid)
 {
        static int (*plibc_func)(uid_t ruid, uid_t euid) = NULL;
+       int (*func)(uid_t ruid, uid_t euid);
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "setreuid");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "setreuid");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"setreuid\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        /* Do the real setreuid */
-       retval = plibc_func(ruid, euid);
+       retval = func(ruid, euid);
        saved_errno = errno;
 
        lttng_ust_after_setreuid();
@@ -207,20 +230,23 @@ int setreuid(uid_t ruid, uid_t euid)
 int setregid(gid_t rgid, gid_t egid)
 {
        static int (*plibc_func)(gid_t rgid, gid_t egid) = NULL;
+       int (*func)(gid_t rgid, gid_t egid);
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "setregid");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "setregid");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"setregid\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        /* Do the real setregid */
-       retval = plibc_func(rgid, egid);
+       retval = func(rgid, egid);
        saved_errno = errno;
 
        lttng_ust_after_setregid();
@@ -253,6 +279,9 @@ int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
        static int (*plibc_func)(int (*fn)(void *), void *child_stack,
                        int flags, void *arg, pid_t *ptid,
                        struct user_desc *tls, pid_t *ctid) = NULL;
+       int (*func)(int (*fn)(void *), void *child_stack,
+                       int flags, void *arg, pid_t *ptid,
+                       struct user_desc *tls, pid_t *ctid);
        /* var args */
        pid_t *ptid;
        struct user_desc *tls;
@@ -268,13 +297,15 @@ int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
        ctid = va_arg(ap, pid_t *);
        va_end(ap);
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "clone");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "clone");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"clone\" symbol.\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        if (flags & CLONE_VM) {
@@ -282,16 +313,16 @@ int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
                 * Creating a thread, no need to intervene, just pass on
                 * the arguments.
                 */
-               retval = plibc_func(fn, child_stack, flags, arg, ptid,
-                               tls, ctid);
+               retval = func(fn, child_stack, flags, arg, ptid,
+                       tls, ctid);
                saved_errno = errno;
        } else {
                /* Creating a real process, we need to intervene. */
                struct ustfork_clone_info info = { .fn = fn, .arg = arg };
 
                lttng_ust_before_fork(&info.sigset);
-               retval = plibc_func(clone_fn, child_stack, flags, &info,
-                               ptid, tls, ctid);
+               retval = func(clone_fn, child_stack, flags, &info,
+                       ptid, tls, ctid);
                saved_errno = errno;
                /* The child doesn't get here. */
                lttng_ust_after_fork_parent(&info.sigset);
@@ -303,20 +334,23 @@ int clone(int (*fn)(void *), void *child_stack, int flags, void *arg, ...)
 int setns(int fd, int nstype)
 {
        static int (*plibc_func)(int fd, int nstype) = NULL;
+       int (*func)(int fd, int nstype);
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "setns");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "setns");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"setns\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        /* Do the real setns */
-       retval = plibc_func(fd, nstype);
+       retval = func(fd, nstype);
        saved_errno = errno;
 
        lttng_ust_after_setns();
@@ -328,20 +362,23 @@ int setns(int fd, int nstype)
 int unshare(int flags)
 {
        static int (*plibc_func)(int flags) = NULL;
+       int (*func)(int flags);
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "unshare");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "unshare");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"unshare\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        /* Do the real setns */
-       retval = plibc_func(flags);
+       retval = func(flags);
        saved_errno = errno;
 
        lttng_ust_after_unshare();
@@ -353,20 +390,23 @@ int unshare(int flags)
 int setresuid(uid_t ruid, uid_t euid, uid_t suid)
 {
        static int (*plibc_func)(uid_t ruid, uid_t euid, uid_t suid) = NULL;
+       int (*func)(uid_t ruid, uid_t euid, uid_t suid);
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "setresuid");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "setresuid");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"setresuid\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        /* Do the real setresuid */
-       retval = plibc_func(ruid, euid, suid);
+       retval = func(ruid, euid, suid);
        saved_errno = errno;
 
        lttng_ust_after_setresuid();
@@ -378,20 +418,23 @@ int setresuid(uid_t ruid, uid_t euid, uid_t suid)
 int setresgid(gid_t rgid, gid_t egid, gid_t sgid)
 {
        static int (*plibc_func)(gid_t rgid, gid_t egid, gid_t sgid) = NULL;
+       int (*func)(gid_t rgid, gid_t egid, gid_t sgid);
        int retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "setresgid");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "setresgid");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"setresgid\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        /* Do the real setresgid */
-       retval = plibc_func(rgid, egid, sgid);
+       retval = func(rgid, egid, sgid);
        saved_errno = errno;
 
        lttng_ust_after_setresgid();
@@ -405,22 +448,25 @@ int setresgid(gid_t rgid, gid_t egid, gid_t sgid)
 pid_t rfork(int flags)
 {
        static pid_t (*plibc_func)(int flags) = NULL;
+       pid_t (*func)(int flags);
        sigset_t sigset;
        pid_t retval;
        int saved_errno;
 
-       if (plibc_func == NULL) {
-               plibc_func = dlsym(RTLD_NEXT, "rfork");
-               if (plibc_func == NULL) {
+       func = uatomic_read(plibc_func);
+       if (func == NULL) {
+               func = dlsym(RTLD_NEXT, "rfork");
+               if (func == NULL) {
                        fprintf(stderr, "libustfork: unable to find \"rfork\" symbol\n");
                        errno = ENOSYS;
                        return -1;
                }
+               uatomic_set(&plibc_func, func);
        }
 
        lttng_ust_before_fork(&sigset);
        /* Do the real rfork */
-       retval = plibc_func(flags);
+       retval = func(flags);
        saved_errno = errno;
        if (retval == 0) {
                /* child */