tunables: Terminate if end of input is reached (CVE-2023-4911)

The string parsing routine may end up writing beyond bounds of tunestr
if the input tunable string is malformed, of the form name=name=val.
This gets processed twice, first as name=name=val and next as name=val,
resulting in tunestr being name=name=val:name=val, thus overflowing
tunestr.

Terminate the parsing loop at the first instance itself so that tunestr
does not overflow.

This also fixes up tst-env-setuid-tunables to actually handle failures
correct and add new tests to validate the fix for this CVE.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
(cherry picked from commit 1056e5b4c3f2d90ed2b4a55f96add28da2f4c8fa)

diff --git a/NEWS b/NEWS
index ae55ffb53ad289b7e3d155bdfef32383a2f459c1..5358e0cbe3f993f2b9d8187f9313ae4e272b8b1d 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -36,6 +36,11 @@ Security related changes:
   an application calls getaddrinfo for AF_INET6 with AI_CANONNAME,
   AI_ALL and AI_V4MAPPED flags set.
 
+  CVE-2023-4911: If a tunable of the form NAME=NAME=VAL is passed in the
+  environment of a setuid program and NAME is valid, it may result in a
+  buffer overflow, which could be exploited to achieve escalated
+  privileges.  This flaw was introduced in glibc 2.34.
+
 The following bugs are resolved with this release:
 
   [12154] Do not fail DNS resolution for CNAMEs which are not host names

diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index 8e7ee9df1049576f4c379d7955106e7811bfc216..76cf8b9da3cdf9c3fcbcff92b377b4934e3d5512 100644 (file)
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -187,11 +187,7 @@ parse_tunables (char *tunestr, char *valstring)
       /* If we reach the end of the string before getting a valid name-value
         pair, bail out.  */
       if (p[len] == '\0')
-       {
-         if (__libc_enable_secure)
-           tunestr[off] = '\0';
-         return;
-       }
+       break;
 
       /* We did not find a valid name-value pair before encountering the
         colon.  */
@@ -251,9 +247,16 @@ parse_tunables (char *tunestr, char *valstring)
            }
        }
 
-      if (p[len] != '\0')
-       p += len + 1;
+      /* We reached the end while processing the tunable string.  */
+      if (p[len] == '\0')
+       break;
+
+      p += len + 1;
     }
+
+  /* Terminate tunestr before we leave.  */
+  if (__libc_enable_secure)
+    tunestr[off] = '\0';
 }
 #endif
 

diff --git a/elf/tst-env-setuid-tunables.c b/elf/tst-env-setuid-tunables.c
index 88182b7b254f1ce919974f1e677c673539028d12..5e9e4c57561437e9b4f27bec5672f56db1b64138 100644 (file)
--- a/elf/tst-env-setuid-tunables.c
+++ b/elf/tst-env-setuid-tunables.c
@@ -52,6 +52,8 @@ const char *teststrings[] =
   "glibc.malloc.perturb=0x800:not_valid.malloc.check=2:glibc.malloc.mmap_threshold=4096",
   "glibc.not_valid.check=2:glibc.malloc.mmap_threshold=4096",
   "not_valid.malloc.check=2:glibc.malloc.mmap_threshold=4096",
+  "glibc.malloc.mmap_threshold=glibc.malloc.mmap_threshold=4096",
+  "glibc.malloc.check=2",
   "glibc.malloc.garbage=2:glibc.maoc.mmap_threshold=4096:glibc.malloc.check=2",
   "glibc.malloc.check=4:glibc.malloc.garbage=2:glibc.maoc.mmap_threshold=4096",
   ":glibc.malloc.garbage=2:glibc.malloc.check=1",
@@ -70,6 +72,8 @@ const char *resultstrings[] =
   "glibc.malloc.perturb=0x800:glibc.malloc.mmap_threshold=4096",
   "glibc.malloc.mmap_threshold=4096",
   "glibc.malloc.mmap_threshold=4096",
+  "glibc.malloc.mmap_threshold=glibc.malloc.mmap_threshold=4096",
+  "",
   "",
   "",
   "",
@@ -84,11 +88,18 @@ test_child (int off)
   const char *val = getenv ("GLIBC_TUNABLES");
 
 #if HAVE_TUNABLES
+  printf ("    [%d] GLIBC_TUNABLES is %s\n", off, val);
+  fflush (stdout);
   if (val != NULL && strcmp (val, resultstrings[off]) == 0)
     return 0;
 
   if (val != NULL)
-    printf ("[%d] Unexpected GLIBC_TUNABLES VALUE %s\n", off, val);
+    printf ("    [%d] Unexpected GLIBC_TUNABLES VALUE %s, expected %s\n",
+           off, val, resultstrings[off]);
+  else
+    printf ("    [%d] GLIBC_TUNABLES environment variable absent\n", off);
+
+  fflush (stdout);
 
   return 1;
 #else
@@ -117,21 +128,26 @@ do_test (int argc, char **argv)
       if (ret != 0)
        exit (1);
 
-      exit (EXIT_SUCCESS);
+      /* Special return code to make sure that the child executed all the way
+        through.  */
+      exit (42);
     }
   else
     {
-      int ret = 0;
-
       /* Spawn tests.  */
       for (int i = 0; i < array_length (teststrings); i++)
        {
          char buf[INT_BUFSIZE_BOUND (int)];
 
-         printf ("Spawned test for %s (%d)\n", teststrings[i], i);
+         printf ("[%d] Spawned test for %s\n", i, teststrings[i]);
          snprintf (buf, sizeof (buf), "%d\n", i);
+         fflush (stdout);
          if (setenv ("GLIBC_TUNABLES", teststrings[i], 1) != 0)
-           exit (1);
+           {
+             printf ("    [%d] Failed to set GLIBC_TUNABLES: %m", i);
+             support_record_failure ();
+             continue;
+           }
 
          int status = support_capture_subprogram_self_sgid (buf);
 
@@ -139,9 +155,14 @@ do_test (int argc, char **argv)
          if (WEXITSTATUS (status) == EXIT_UNSUPPORTED)
            return EXIT_UNSUPPORTED;
 
-         ret |= status;
+         if (WEXITSTATUS (status) != 42)
+           {
+             printf ("    [%d] child failed with status %d\n", i,
+                     WEXITSTATUS (status));
+             support_record_failure ();
+           }
        }
-      return ret;
+      return 0;
     }
 }