tmpfs: fix oops on mounts with mpol=default

Fix an 'oops' when a tmpfs mount point is mounted with the mpol=default mempolicy. Upon remounting a tmpfs mount point with 'mpol=default' option, the mount code crashed with a null pointer dereference. The initial problem report was on 2.6.27, but the problem exists in mainline 2.6.34-rc as well. On examining the code, we see that mpol_new returns NULL if default mempolicy was requested. This 'NULL' mempolicy is accessed to store the node mask resulting in oops. The following patch fixes it. Signed-off-by: Ravikiran Thirumalai <[email protected]> Signed-off-by: KOSAKI Motohiro <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: Mel Gorman <[email protected]> Acked-by: Lee Schermerhorn <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
chewitt · Mar 24, 2010 · 413b43d · 413b43d
1 parent 8c363af
commit 413b43d
Showing 1 changed file with 7 additions and 2 deletions.
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
@@ -2215,10 +2215,15 @@ int mpol_parse_str(char *str, struct mempolicy **mpol, int no_context)
 			goto out;
 		mode = MPOL_PREFERRED;
 		break;
-
+	case MPOL_DEFAULT:
+		/*
+		 * Insist on a empty nodelist
+		 */
+		if (!nodelist)
+			err = 0;
+		goto out;
 	/*
 	 * case MPOL_BIND:    mpol_new() enforces non-empty nodemask.
-	 * case MPOL_DEFAULT: mpol_new() enforces empty nodemask, ignores flags.
 	 */
 	}