elf: Do not process invalid tunable format

Tunable definitions with more than one '=' on are parsed and enabled,
and any subsequent '=' are ignored.  It means that tunables in the form
'tunable=tunable=value' or 'tunable=value=value' are handled as
'tunable=value'.  These inputs are likely user input errors, which
should not be accepted.

Checked on x86_64-linux-gnu.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

2 files changed, 21 insertions, 7 deletions

diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index f7dca8f7c1..082a76d9c4 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -192,10 +192,12 @@ parse_tunables (char *valstring)
 
       const char *value = p;
 
-      while (*p != ':' && *p != '\0')
+      while (*p != '=' && *p != ':' && *p != '\0')
 	p++;
 
-      if (*p == '\0')
+      if (*p == '=')
+	break;
+      else if (*p == '\0')
 	done = true;
       else
 	*p++ = '\0';
diff --git a/elf/tst-tunables.c b/elf/tst-tunables.c
index d874b73b68..7fe9907e05 100644
--- a/elf/tst-tunables.c
+++ b/elf/tst-tunables.c
@@ -161,24 +161,36 @@ static const struct test_t
     0,
     0,
   },
-  /* The ill-formatted tunable is also skipped.  */
+  /* If there is a ill-formatted key=value, everything after is also ignored.  */
   {
     "glibc.malloc.mmap_threshold=glibc.malloc.mmap_threshold=4096:glibc.malloc.check=2",
-    2,
+    0,
     0,
     0,
   },
-  /* For an integer tunable, parse will stop on non number character.  */
   {
     "glibc.malloc.check=2=2",
-    2,
+    0,
     0,
     0,
   },
   {
     "glibc.malloc.check=2=2:glibc.malloc.mmap_threshold=4096",
+    0,
+    0,
+    0,
+  },
+  {
+    "glibc.malloc.check=2=2:glibc.malloc.check=2",
+    0,
+    0,
+    0,
+  },
+  /* Valid tunables set before ill-formatted ones are set.  */
+  {
+    "glibc.malloc.check=2:glibc.malloc.mmap_threshold=4096=4096",
     2,
-    4096,
+    0,
     0,
   }
 };