# HG changeset patch # User Roman Arutyunyan # Date 1453816019 -10800 # Node ID 497d0cff8acef33f7c08b21f35911201d863ac9a # Parent a5767988c0222825dd1ee58e110b71d804b63878 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 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. diff --git a/src/core/ngx_resolver.c b/src/core/ngx_resolver.c --- a/src/core/ngx_resolver.c +++ b/src/core/ngx_resolver.c @@ -59,7 +59,7 @@ ngx_int_t ngx_udp_connect(ngx_udp_connec static void ngx_resolver_cleanup(void *data); static void ngx_resolver_cleanup_tree(ngx_resolver_t *r, ngx_rbtree_t *tree); static ngx_int_t ngx_resolve_name_locked(ngx_resolver_t *r, - ngx_resolver_ctx_t *ctx); + ngx_resolver_ctx_t *ctx, ngx_str_t *name); static void ngx_resolver_expire(ngx_resolver_t *r, ngx_rbtree_t *tree, ngx_queue_t *queue); static ngx_int_t ngx_resolver_send_query(ngx_resolver_t *r, @@ -376,7 +376,7 @@ ngx_resolve_name(ngx_resolver_ctx_t *ctx /* lock name mutex */ - rc = ngx_resolve_name_locked(r, ctx); + rc = ngx_resolve_name_locked(r, ctx, &ctx->name); if (rc == NGX_OK) { return NGX_OK; @@ -403,7 +403,6 @@ ngx_resolve_name(ngx_resolver_ctx_t *ctx void ngx_resolve_name_done(ngx_resolver_ctx_t *ctx) { - uint32_t hash; ngx_resolver_t *r; ngx_resolver_ctx_t *w, **p; ngx_resolver_node_t *rn; @@ -425,9 +424,7 @@ ngx_resolve_name_done(ngx_resolver_ctx_t if (ctx->state == NGX_AGAIN || ctx->state == NGX_RESOLVE_TIMEDOUT) { - hash = ngx_crc32_short(ctx->name.data, ctx->name.len); - - rn = ngx_resolver_lookup_name(r, &ctx->name, hash); + rn = ctx->node; if (rn) { p = &rn->waiting; @@ -472,20 +469,22 @@ done: static ngx_int_t -ngx_resolve_name_locked(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx) +ngx_resolve_name_locked(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx, + ngx_str_t *name) { uint32_t hash; ngx_int_t rc; + ngx_str_t cname; ngx_uint_t naddrs; ngx_addr_t *addrs; ngx_resolver_ctx_t *next, *last; ngx_resolver_node_t *rn; - ngx_strlow(ctx->name.data, ctx->name.data, ctx->name.len); - - hash = ngx_crc32_short(ctx->name.data, ctx->name.len); - - rn = ngx_resolver_lookup_name(r, &ctx->name, hash); + ngx_strlow(name->data, name->data, name->len); + + hash = ngx_crc32_short(name->data, name->len); + + rn = ngx_resolver_lookup_name(r, name, hash); if (rn) { @@ -559,10 +558,10 @@ ngx_resolve_name_locked(ngx_resolver_t * if (ctx->recursion++ < NGX_RESOLVER_MAX_RECURSION) { - ctx->name.len = rn->cnlen; - ctx->name.data = rn->u.cname; - - return ngx_resolve_name_locked(r, ctx); + cname.len = rn->cnlen; + cname.data = rn->u.cname; + + return ngx_resolve_name_locked(r, ctx, &cname); } last->next = rn->waiting; @@ -602,6 +601,11 @@ ngx_resolve_name_locked(ngx_resolver_t * rn->waiting = ctx; ctx->state = NGX_AGAIN; + do { + ctx->node = rn; + ctx = ctx->next; + } while (ctx); + return NGX_AGAIN; } @@ -640,14 +644,14 @@ ngx_resolve_name_locked(ngx_resolver_t * return NGX_ERROR; } - rn->name = ngx_resolver_dup(r, ctx->name.data, ctx->name.len); + rn->name = ngx_resolver_dup(r, name->data, name->len); if (rn->name == NULL) { ngx_resolver_free(r, rn); return NGX_ERROR; } rn->node.key = hash; - rn->nlen = (u_short) ctx->name.len; + rn->nlen = (u_short) name->len; rn->query = NULL; #if (NGX_HAVE_INET6) rn->query6 = NULL; @@ -656,7 +660,7 @@ ngx_resolve_name_locked(ngx_resolver_t * ngx_rbtree_insert(&r->name_rbtree, &rn->node); } - rc = ngx_resolver_create_name_query(r, rn, &ctx->name); + rc = ngx_resolver_create_name_query(r, rn, name); if (rc == NGX_ERROR) { goto failed; @@ -720,6 +724,11 @@ ngx_resolve_name_locked(ngx_resolver_t * ctx->state = NGX_AGAIN; + do { + ctx->node = rn; + ctx = ctx->next; + } while (ctx); + return NGX_AGAIN; failed: @@ -842,6 +851,7 @@ ngx_resolve_addr(ngx_resolver_ctx_t *ctx ctx->next = rn->waiting; rn->waiting = ctx; ctx->state = NGX_AGAIN; + ctx->node = rn; /* unlock addr mutex */ @@ -927,6 +937,7 @@ ngx_resolve_addr(ngx_resolver_ctx_t *ctx /* unlock addr mutex */ ctx->state = NGX_AGAIN; + ctx->node = rn; return NGX_OK; @@ -957,17 +968,11 @@ failed: void ngx_resolve_addr_done(ngx_resolver_ctx_t *ctx) { - in_addr_t addr; ngx_queue_t *expire_queue; ngx_rbtree_t *tree; ngx_resolver_t *r; ngx_resolver_ctx_t *w, **p; - struct sockaddr_in *sin; ngx_resolver_node_t *rn; -#if (NGX_HAVE_INET6) - uint32_t hash; - struct sockaddr_in6 *sin6; -#endif r = ctx->resolver; @@ -996,21 +1001,7 @@ ngx_resolve_addr_done(ngx_resolver_ctx_t if (ctx->state == NGX_AGAIN || ctx->state == NGX_RESOLVE_TIMEDOUT) { - switch (ctx->addr.sockaddr->sa_family) { - -#if (NGX_HAVE_INET6) - case AF_INET6: - sin6 = (struct sockaddr_in6 *) ctx->addr.sockaddr; - hash = ngx_crc32_short(sin6->sin6_addr.s6_addr, 16); - rn = ngx_resolver_lookup_addr6(r, &sin6->sin6_addr, hash); - break; -#endif - - default: /* AF_INET */ - sin = (struct sockaddr_in *) ctx->addr.sockaddr; - addr = ntohl(sin->sin_addr.s_addr); - rn = ngx_resolver_lookup_addr(r, addr); - } + rn = ctx->node; if (rn) { p = &rn->waiting; @@ -2014,9 +2005,12 @@ ngx_resolver_process_a(ngx_resolver_t *r rn->waiting = NULL; if (ctx) { - ctx->name = name; - - (void) ngx_resolve_name_locked(r, ctx); + + for (next = ctx; next; next = next->next) { + next->node = NULL; + } + + (void) ngx_resolve_name_locked(r, ctx, &name); } ngx_resolver_free(r, rn->query); diff --git a/src/core/ngx_resolver.h b/src/core/ngx_resolver.h --- a/src/core/ngx_resolver.h +++ b/src/core/ngx_resolver.h @@ -161,6 +161,8 @@ struct ngx_resolver_ctx_s { ngx_uint_t quick; /* unsigned quick:1; */ ngx_uint_t recursion; ngx_event_t *event; + + ngx_resolver_node_t *node; };