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Re: svn commit: r1850651 - /subversion/trunk/subversion/mod_dav_svn/repos.c

From: Sergey Raevskiy <Sergey.Raevskiy_at_visualsvn.com>
Date: Thu, 15 Aug 2019 20:14:43 +0300

> /* if an authenticated username is present, attach it to the FS */
> if (r->user)
> @@ -2503,6 +2529,14 @@ get_resource(request_rec *r,
> apr_pool_cleanup_register(r->pool, cleanup_baton, cleanup_fs_access,
> apr_pool_cleanup_null);
>
> + /* We must degrade the logging context when the request is freed. */
> + cleanup_req_logging_baton =
> + apr_pcalloc(r->pool, sizeof(*cleanup_req_logging_baton));
> + cleanup_req_logging_baton->fs = repos->fs;
> + cleanup_req_logging_baton->connection = r->connection;
> + apr_pool_pre_cleanup_register(r->pool, cleanup_req_logging_baton,
> + cleanup_req_logging);

Is it intended to set-up this cleanup handler only if R->USER is specified?

On Mon, Jan 7, 2019 at 6:04 PM <stsp_at_apache.org> wrote:
>
> Author: stsp
> Date: Mon Jan 7 15:04:15 2019
> New Revision: 1850651
>
> URL: http://svn.apache.org/viewvc?rev=1850651&view=rev
> Log:
> Fix a use-after-free in mod_dav_svn's logging of FS warnings.
>
> The FS warning callback could be called with a request context that had
> already been deallocated. This resulted in a crash during 'make check'
> with ra_serf on OpenBSD. The problem was even documented in a comment:
>
> /* ### hmm. the FS is cleaned up at request cleanup time. "r" might
> ### not really be valid. we should probably put the FS into a
> ### subpool to ensure it gets cleaned before the request.
> ### is there a good way to create and use a subpool for all
> ### of our functions ... ??
> */
>
> Rather than putting the FS into a subpool, the solution implemented with this
> commit installs a pre-cleanup handler on the request pool, which switches the
> logging context from the request to its associated connection. This avoids the
> use-after-free at the cost of a less precise logging context.
>
> Suggested by: stefan2
> https://svn.haxx.se/dev/archive-2018-12/0145.shtml
>
> * subversion/mod_dav_svn/repos.c
> (log_warning): Rename to ...
> (log_warning_req): ... this.
> (log_warning_conn): New logging helper which uses a connection context.
> (cleanup_req_logging_baton, cleanup_req_logging): New APR pool cleanup
> handler which switches FS logging context from a request to a connection.
> (get_resource): Install aforementioned pool cleanup handler.
>
> Modified:
> subversion/trunk/subversion/mod_dav_svn/repos.c
>
> Modified: subversion/trunk/subversion/mod_dav_svn/repos.c
> URL: http://svn.apache.org/viewvc/subversion/trunk/subversion/mod_dav_svn/repos.c?rev=1850651&r1=1850650&r2=1850651&view=diff
> ==============================================================================
> --- subversion/trunk/subversion/mod_dav_svn/repos.c (original)
> +++ subversion/trunk/subversion/mod_dav_svn/repos.c Mon Jan 7 15:04:15 2019
> @@ -1225,25 +1225,32 @@ create_private_resource(const dav_resour
> return &comb->res;
> }
>
> -
> -static void log_warning(void *baton, svn_error_t *err)
> +static void log_warning_req(void *baton, svn_error_t *err)
> {
> request_rec *r = baton;
> const char *continuation = "";
>
> - /* ### hmm. the FS is cleaned up at request cleanup time. "r" might
> - ### not really be valid. we should probably put the FS into a
> - ### subpool to ensure it gets cleaned before the request.
> + /* Not showing file/line so no point in tracing */
> + err = svn_error_purge_tracing(err);
> + while (err)
> + {
> + ap_log_rerror(APLOG_MARK, APLOG_ERR, APR_EGENERAL, r, "%s%s",
> + continuation, err->message);
> + continuation = "-";
> + err = err->child;
> + }
> +}
>
> - ### is there a good way to create and use a subpool for all
> - ### of our functions ... ??
> - */
> +static void log_warning_conn(void *baton, svn_error_t *err)
> +{
> + conn_rec *c = baton;
> + const char *continuation = "";
>
> /* Not showing file/line so no point in tracing */
> err = svn_error_purge_tracing(err);
> while (err)
> {
> - ap_log_rerror(APLOG_MARK, APLOG_ERR, APR_EGENERAL, r, "%s%s",
> + ap_log_cerror(APLOG_MARK, APLOG_ERR, APR_EGENERAL, c, "%s%s",
> continuation, err->message);
> continuation = "-";
> err = err->child;
> @@ -1547,6 +1554,24 @@ cleanup_fs_access(void *data)
> return APR_SUCCESS;
> }
>
> +/* Context for cleanup handler. */
> +struct cleanup_req_logging_baton
> +{
> + svn_fs_t *fs;
> + conn_rec *connection;
> +};
> +
> +static apr_status_t
> +cleanup_req_logging(void *data)
> +{
> + struct cleanup_req_logging_baton *baton = data;
> +
> + /* The request about to be freed. Log future warnings with a connection
> + * context instead of a request context. */
> + svn_fs_set_warning_func(baton->fs, log_warning_conn, baton->connection);
> +
> + return APR_SUCCESS;
> +}
>
> /* Helper func to construct a special 'parentpath' private resource. */
> static dav_error *
> @@ -2180,6 +2205,7 @@ get_resource(request_rec *r,
> int had_slash;
> dav_locktoken_list *ltl;
> struct cleanup_fs_access_baton *cleanup_baton;
> + struct cleanup_req_logging_baton *cleanup_req_logging_baton;
> void *userdata;
> apr_hash_t *fs_config;
>
> @@ -2486,7 +2512,7 @@ get_resource(request_rec *r,
> repos->fs = svn_repos_fs(repos->repos);
>
> /* capture warnings during cleanup of the FS */
> - svn_fs_set_warning_func(repos->fs, log_warning, r);
> + svn_fs_set_warning_func(repos->fs, log_warning_req, r);
>
> /* if an authenticated username is present, attach it to the FS */
> if (r->user)
> @@ -2503,6 +2529,14 @@ get_resource(request_rec *r,
> apr_pool_cleanup_register(r->pool, cleanup_baton, cleanup_fs_access,
> apr_pool_cleanup_null);
>
> + /* We must degrade the logging context when the request is freed. */
> + cleanup_req_logging_baton =
> + apr_pcalloc(r->pool, sizeof(*cleanup_req_logging_baton));
> + cleanup_req_logging_baton->fs = repos->fs;
> + cleanup_req_logging_baton->connection = r->connection;
> + apr_pool_pre_cleanup_register(r->pool, cleanup_req_logging_baton,
> + cleanup_req_logging);
> +
> /* Create an access context based on the authenticated username. */
> serr = svn_fs_create_access(&access_ctx, r->user, r->pool);
> if (serr)
>
>
Received on 2019-08-15 19:15:00 CEST

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