From: Frank Schaefer <kelledin@gmail.com>
Date: Thu, 4 Oct 2018 21:06:16 +0000 (-0500)
Subject:  * hack around deficiencies in prctl() PR_SET_MM_*
X-Git-Tag: v240~624
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=14ee72b7d8de34a6b02767b865c3c49ceef2ed84;p=thirdparty%2Fsystemd.git

 * hack around deficiencies in prctl() PR_SET_MM_*
---

diff --git a/src/basic/process-util.c b/src/basic/process-util.c
index 1098cf453f6..a02ceb79e54 100644
--- a/src/basic/process-util.c
+++ b/src/basic/process-util.c
@@ -336,15 +336,33 @@ int rename_process(const char name[]) {
 
                 /* Now, let's tell the kernel about this new memory */
                 if (prctl(PR_SET_MM, PR_SET_MM_ARG_START, (unsigned long) nn, 0, 0) < 0) {
-                        log_debug_errno(errno, "PR_SET_MM_ARG_START failed, proceeding without: %m");
-                        (void) munmap(nn, nn_size);
-                        goto use_saved_argv;
-                }
+                        /* HACK: prctl() API is kind of dumb on this point.  The existing end address may already be
+                         * below the desired start address, in which case the kernel may have kicked this back due
+                         * to a range-check failure (see linux/kernel/sys.c:validate_prctl_map() to see this in
+                         * action).  The proper solution would be to have a prctl() API that could set both start+end
+                         * simultaneously, or at least let us query the existing address to anticipate this condition
+                         * and respond accordingly.  For now, we can only guess at the cause of this failure and try
+                         * a workaround--which will briefly expand the arg space to something potentially huge before
+                         * resizing it to what we want. */
+                        log_debug_errno(errno, "PR_SET_MM_ARG_START failed, attempting PR_SET_MM_ARG_END hack: %m");
+
+                        if (prctl(PR_SET_MM, PR_SET_MM_ARG_END, (unsigned long) nn + l + 1, 0, 0) < 0) {
+                                log_debug_errno(errno, "PR_SET_MM_ARG_END hack failed, proceeding without: %m");
+                                (void) munmap(nn, nn_size);
+                                goto use_saved_argv;
+                        }
 
-                /* And update the end pointer to the new end, too. If this fails, we don't really know what to do, it's
-                 * pretty unlikely that we can rollback, hence we'll just accept the failure, and continue. */
-                if (prctl(PR_SET_MM, PR_SET_MM_ARG_END, (unsigned long) nn + l + 1, 0, 0) < 0)
-                        log_debug_errno(errno, "PR_SET_MM_ARG_END failed, proceeding without: %m");
+                        if (prctl(PR_SET_MM, PR_SET_MM_ARG_START, (unsigned long) nn, 0, 0) < 0) {
+                                log_debug_errno(errno, "PR_SET_MM_ARG_START still failed, proceeding without: %m");
+                                goto use_saved_argv;
+                        }
+                } else {
+                        /* And update the end pointer to the new end, too. If this fails, we don't really know what
+                         * to do, it's pretty unlikely that we can rollback, hence we'll just accept the failure,
+                         * and continue. */
+                        if (prctl(PR_SET_MM, PR_SET_MM_ARG_END, (unsigned long) nn + l + 1, 0, 0) < 0)
+                                log_debug_errno(errno, "PR_SET_MM_ARG_END failed, proceeding without: %m");
+                }
 
                 if (mm)
                         (void) munmap(mm, mm_size);