Check that length of data returned by sysctl is non-zero

The length of the data returned by sysctl can be zero, which was not
checked for.  This could cause crashes, e.g. when querying
non-existent processes.  (Bug#36279)

* src/sysdep.c (list_system_processes) [DARWIN_OS || __FreeBSD__]:
(system_process_attributes) [__FreeBSD__]:
(system_process_attributes) [DARWIN_OS]:
* src/filelock.c (get_boot_time) [CTL_KERN && KERN_BOOTTIME]: Check
  for zero length data returned by sysctl.

2 files changed, 6 insertions, 6 deletions

diff --git a/src/filelock.c b/src/filelock.c
index 81d98f36fa4..bcd5bff563d 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -152,7 +152,7 @@ get_boot_time (void)
     mib[1] = KERN_BOOTTIME;
     size = sizeof (boottime_val);
 
-    if (sysctl (mib, 2, &boottime_val, &size, NULL, 0) >= 0)
+    if (sysctl (mib, 2, &boottime_val, &size, NULL, 0) >= 0 && size != 0)
       {
         boot_time = boottime_val.tv_sec;
         return boot_time;
diff --git a/src/sysdep.c b/src/sysdep.c
index 1e35e06b633..b2aecc0ddac 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -3014,11 +3014,11 @@ list_system_processes (void)
 
   Lisp_Object proclist = Qnil;
 
-  if (sysctl (mib, 3, NULL, &len, NULL, 0) != 0)
+  if (sysctl (mib, 3, NULL, &len, NULL, 0) != 0 || len == 0)
     return proclist;
 
   procs = xmalloc (len);
-  if (sysctl (mib, 3, procs, &len, NULL, 0) != 0)
+  if (sysctl (mib, 3, procs, &len, NULL, 0) != 0 || len == 0)
     {
       xfree (procs);
       return proclist;
@@ -3618,7 +3618,7 @@ system_process_attributes (Lisp_Object pid)
   CONS_TO_INTEGER (pid, int, proc_id);
   mib[3] = proc_id;
 
-  if (sysctl (mib, 4, &proc, &proclen, NULL, 0) != 0)
+  if (sysctl (mib, 4, &proc, &proclen, NULL, 0) != 0 || proclen == 0)
     return attrs;
 
   attrs = Fcons (Fcons (Qeuid, make_fixnum_or_float (proc.ki_uid)), attrs);
@@ -3740,7 +3740,7 @@ system_process_attributes (Lisp_Object pid)
 
   mib[2] = KERN_PROC_ARGS;
   len = MAXPATHLEN;
-  if (sysctl (mib, 4, args, &len, NULL, 0) == 0)
+  if (sysctl (mib, 4, args, &len, NULL, 0) == 0 && len != 0)
     {
       int i;
       for (i = 0; i < len; i++)
@@ -3798,7 +3798,7 @@ system_process_attributes (Lisp_Object pid)
   CONS_TO_INTEGER (pid, int, proc_id);
   mib[3] = proc_id;
 
-  if (sysctl (mib, 4, &proc, &proclen, NULL, 0) != 0)
+  if (sysctl (mib, 4, &proc, &proclen, NULL, 0) != 0 || proclen == 0)
     return attrs;
 
   uid = proc.kp_eproc.e_ucred.cr_uid;