Mercurial > hg > nginx

view src/core/ngx_shmtx.c @ 6351:497d0cff8ace

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Resolver: fixed use-after-free memory accesses with CNAME. When several requests were waiting for a response, then after getting a CNAME response only the last request's context had the name updated. Contexts of other requests had the wrong name. This name was used by ngx_resolve_name_done() to find the node to remove the request context from. When the name was wrong, the request could not be properly cancelled, its context was freed but stayed linked to the node's waiting list. This happened e.g. when the first request was aborted or timed out before the resolving completed. When it completed, this triggered a use-after-free memory access by calling ctx->handler of already freed request context. The bug manifests itself by "could not cancel <name> resolving" alerts in error_log. When a request was responded with a CNAME, the request context kept the pointer to the original node's rn->u.cname. If the original node expired before the resolving timed out or completed with an error, this would trigger a use-after-free memory access via ctx->name in ctx->handler(). The fix is to keep ctx->name unmodified. The name from context is no longer used by ngx_resolve_name_done(). Instead, we now keep the pointer to resolver node to which this request is linked. Keeping the original name intact also improves logging.
author Roman Arutyunyan <arut@nginx.com>
date Tue, 26 Jan 2016 16:46:59 +0300
parents 860a1c37f3b2
children
line wrap: on
line source


/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>


#if (NGX_HAVE_ATOMIC_OPS)


static void ngx_shmtx_wakeup(ngx_shmtx_t *mtx);


ngx_int_t
ngx_shmtx_create(ngx_shmtx_t *mtx, ngx_shmtx_sh_t *addr, u_char *name)
{
    mtx->lock = &addr->lock;

    if (mtx->spin == (ngx_uint_t) -1) {
        return NGX_OK;
    }

    mtx->spin = 2048;

#if (NGX_HAVE_POSIX_SEM)

    mtx->wait = &addr->wait;

    if (sem_init(&mtx->sem, 1, 0) == -1) {
        ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, ngx_errno,
                      "sem_init() failed");
    } else {
        mtx->semaphore = 1;
    }

#endif

    return NGX_OK;
}


void
ngx_shmtx_destroy(ngx_shmtx_t *mtx)
{
#if (NGX_HAVE_POSIX_SEM)

    if (mtx->semaphore) {
        if (sem_destroy(&mtx->sem) == -1) {
            ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, ngx_errno,
                          "sem_destroy() failed");
        }
    }

#endif
}


ngx_uint_t
ngx_shmtx_trylock(ngx_shmtx_t *mtx)
{
    return (*mtx->lock == 0 && ngx_atomic_cmp_set(mtx->lock, 0, ngx_pid));
}


void
ngx_shmtx_lock(ngx_shmtx_t *mtx)
{
    ngx_uint_t         i, n;

    ngx_log_debug0(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0, "shmtx lock");

    for ( ;; ) {

        if (*mtx->lock == 0 && ngx_atomic_cmp_set(mtx->lock, 0, ngx_pid)) {
            return;
        }

        if (ngx_ncpu > 1) {

            for (n = 1; n < mtx->spin; n <<= 1) {

                for (i = 0; i < n; i++) {
                    ngx_cpu_pause();
                }

                if (*mtx->lock == 0
                    && ngx_atomic_cmp_set(mtx->lock, 0, ngx_pid))
                {
                    return;
                }
            }
        }

#if (NGX_HAVE_POSIX_SEM)

        if (mtx->semaphore) {
            (void) ngx_atomic_fetch_add(mtx->wait, 1);

            if (*mtx->lock == 0 && ngx_atomic_cmp_set(mtx->lock, 0, ngx_pid)) {
                (void) ngx_atomic_fetch_add(mtx->wait, -1);
                return;
            }

            ngx_log_debug1(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
                           "shmtx wait %uA", *mtx->wait);

            while (sem_wait(&mtx->sem) == -1) {
                ngx_err_t  err;

                err = ngx_errno;

                if (err != NGX_EINTR) {
                    ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, err,
                                  "sem_wait() failed while waiting on shmtx");
                    break;
                }
            }

            ngx_log_debug0(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
                           "shmtx awoke");

            continue;
        }

#endif

        ngx_sched_yield();
    }
}


void
ngx_shmtx_unlock(ngx_shmtx_t *mtx)
{
    if (mtx->spin != (ngx_uint_t) -1) {
        ngx_log_debug0(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0, "shmtx unlock");
    }

    if (ngx_atomic_cmp_set(mtx->lock, ngx_pid, 0)) {
        ngx_shmtx_wakeup(mtx);
    }
}


ngx_uint_t
ngx_shmtx_force_unlock(ngx_shmtx_t *mtx, ngx_pid_t pid)
{
    ngx_log_debug0(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
                   "shmtx forced unlock");

    if (ngx_atomic_cmp_set(mtx->lock, pid, 0)) {
        ngx_shmtx_wakeup(mtx);
        return 1;
    }

    return 0;
}


static void
ngx_shmtx_wakeup(ngx_shmtx_t *mtx)
{
#if (NGX_HAVE_POSIX_SEM)
    ngx_atomic_uint_t  wait;

    if (!mtx->semaphore) {
        return;
    }

    for ( ;; ) {

        wait = *mtx->wait;

        if ((ngx_atomic_int_t) wait <= 0) {
            return;
        }

        if (ngx_atomic_cmp_set(mtx->wait, wait, wait - 1)) {
            break;
        }
    }

    ngx_log_debug1(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
                   "shmtx wake %uA", wait);

    if (sem_post(&mtx->sem) == -1) {
        ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, ngx_errno,
                      "sem_post() failed while wake shmtx");
    }

#endif
}


#else


ngx_int_t
ngx_shmtx_create(ngx_shmtx_t *mtx, ngx_shmtx_sh_t *addr, u_char *name)
{
    if (mtx->name) {

        if (ngx_strcmp(name, mtx->name) == 0) {
            mtx->name = name;
            return NGX_OK;
        }

        ngx_shmtx_destroy(mtx);
    }

    mtx->fd = ngx_open_file(name, NGX_FILE_RDWR, NGX_FILE_CREATE_OR_OPEN,
                            NGX_FILE_DEFAULT_ACCESS);

    if (mtx->fd == NGX_INVALID_FILE) {
        ngx_log_error(NGX_LOG_EMERG, ngx_cycle->log, ngx_errno,
                      ngx_open_file_n " \"%s\" failed", name);
        return NGX_ERROR;
    }

    if (ngx_delete_file(name) == NGX_FILE_ERROR) {
        ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, ngx_errno,
                      ngx_delete_file_n " \"%s\" failed", name);
    }

    mtx->name = name;

    return NGX_OK;
}


void
ngx_shmtx_destroy(ngx_shmtx_t *mtx)
{
    if (ngx_close_file(mtx->fd) == NGX_FILE_ERROR) {
        ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, ngx_errno,
                      ngx_close_file_n " \"%s\" failed", mtx->name);
    }
}


ngx_uint_t
ngx_shmtx_trylock(ngx_shmtx_t *mtx)
{
    ngx_err_t  err;

    err = ngx_trylock_fd(mtx->fd);

    if (err == 0) {
        return 1;
    }

    if (err == NGX_EAGAIN) {
        return 0;
    }

#if __osf__ /* Tru64 UNIX */

    if (err == NGX_EACCES) {
        return 0;
    }

#endif

    ngx_log_abort(err, ngx_trylock_fd_n " %s failed", mtx->name);

    return 0;
}


void
ngx_shmtx_lock(ngx_shmtx_t *mtx)
{
    ngx_err_t  err;

    err = ngx_lock_fd(mtx->fd);

    if (err == 0) {
        return;
    }

    ngx_log_abort(err, ngx_lock_fd_n " %s failed", mtx->name);
}


void
ngx_shmtx_unlock(ngx_shmtx_t *mtx)
{
    ngx_err_t  err;

    err = ngx_unlock_fd(mtx->fd);

    if (err == 0) {
        return;
    }

    ngx_log_abort(err, ngx_unlock_fd_n " %s failed", mtx->name);
}


ngx_uint_t
ngx_shmtx_force_unlock(ngx_shmtx_t *mtx, ngx_pid_t pid)
{
    return 0;
}

#endif