mm, mempolicy: make mpol_to_str robust and always succeed

mpol_to_str() should not fail. Currently, it either fails because the string buffer is too small or because a string hasn't been defined for a mempolicy mode. If a new mempolicy mode is introduced and no string is defined for it, just warn and return "unknown". If the buffer is too small, just truncate the string and return, the same behavior as snprintf(). This also fixes a bug where there was no NULL-byte termination when doing *p++ = '=' and *p++ ':' and maxlen has been reached. Signed-off-by: David Rientjes <rientjes@google.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Chen Gang <gang.chen@asianux.com> Cc: Rik van Riel <riel@redhat.com> Cc: Dave Jones <davej@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm, mempolicy: make mpol_to_str robust and always succeed
mpol_to_str() should not fail. Currently, it either fails because the string buffer is too small or because a string hasn't been defined for a mempolicy mode. If a new mempolicy mode is introduced and no string is defined for it, just warn and return "unknown". If the buffer is too small, just truncate the string and return, the same behavior as snprintf(). This also fixes a bug where there was no NULL-byte termination when doing *p++ = '=' and *p++ ':' and maxlen has been reached. Signed-off-by: David Rientjes <rientjes@google.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Chen Gang <gang.chen@asianux.com> Cc: Rik van Riel <riel@redhat.com> Cc: Dave Jones <davej@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
David Rientjes · Linus Torvalds
1 parent 40c3baa7c6
Showing 3 changed files with 24 additions and 47 deletions Side-by-side Diff
fs/proc/task_mmu.c
include/linux/mempolicy.h
mm/mempolicy.c
@@ -1387,8 +1387,8 @@
 	struct mm_struct *mm = vma->vm_mm;
 	struct mm_walk walk = {};
 	struct mempolicy *pol;
-	int n;
-	char buffer[50];
+	char buffer[64];
+	int nid;
  
 	if (!mm)
 		return 0;
  
@@ -1404,10 +1404,8 @@
 	walk.mm = mm;
  
 	pol = get_vma_policy(task, vma, vma->vm_start);
-	n = mpol_to_str(buffer, sizeof(buffer), pol);
+	mpol_to_str(buffer, sizeof(buffer), pol);
 	mpol_cond_put(pol);
-	if (n < 0)
-		return n;
  
 	seq_printf(m, "%08lx %s", vma->vm_start, buffer);
  
@@ -1460,9 +1458,9 @@
 	if (md->writeback)
 		seq_printf(m, " writeback=%lu", md->writeback);
  
-	for_each_node_state(n, N_MEMORY)
-		if (md->node[n])
-			seq_printf(m, " N%d=%lu", n, md->node[n]);
+	for_each_node_state(nid, N_MEMORY)
+		if (md->node[nid])
+			seq_printf(m, " N%d=%lu", nid, md->node[nid]);
 out:
 	seq_putc(m, '\n');
  
@@ -169,7 +169,7 @@
 extern int mpol_parse_str(char *str, struct mempolicy **mpol);
 #endif
  
-extern int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol);
+extern void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol);
  
 /* Check if a vma is migratable */
 static inline int vma_migratable(struct vm_area_struct *vma)
  
@@ -307,9 +307,8 @@
 }
 #endif
  
-static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
+static inline void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 {
-	return 0;
 }
  
 static inline int mpol_misplaced(struct page *page, struct vm_area_struct *vma,
@@ -2914,62 +2914,45 @@
  * @maxlen:  length of @buffer
  * @pol:  pointer to mempolicy to be formatted
  *
- * Convert a mempolicy into a string.
- * Returns the number of characters in buffer (if positive)
- * or an error (negative)
+ * Convert @pol into a string.  If @buffer is too short, truncate the string.
+ * Recommend a @maxlen of at least 32 for the longest mode, "interleave", the
+ * longest flag, "relative", and to display at least a few node ids.
  */
-int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
+void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 {
 	char *p = buffer;
-	int l;
-	nodemask_t nodes;
-	unsigned short mode;
-	unsigned short flags = pol ? pol->flags : 0;
+	nodemask_t nodes = NODE_MASK_NONE;
+	unsigned short mode = MPOL_DEFAULT;
+	unsigned short flags = 0;
  
-	/*
-	 * Sanity check:  room for longest mode, flag and some nodes
-	 */
-	VM_BUG_ON(maxlen < strlen("interleave") + strlen("relative") + 16);
-
-	if (!pol || pol == &default_policy)
-		mode = MPOL_DEFAULT;
-	else
+	if (pol && pol != &default_policy) {
 		mode = pol->mode;
+		flags = pol->flags;
+	}
  
 	switch (mode) {
 	case MPOL_DEFAULT:
-		nodes_clear(nodes);
 		break;
-
 	case MPOL_PREFERRED:
-		nodes_clear(nodes);
 		if (flags & MPOL_F_LOCAL)
 			mode = MPOL_LOCAL;
 		else
 			node_set(pol->v.preferred_node, nodes);
 		break;
-
 	case MPOL_BIND:
-		/* Fall through */
 	case MPOL_INTERLEAVE:
 		nodes = pol->v.nodes;
 		break;
-
 	default:
-		return -EINVAL;
+		WARN_ON_ONCE(1);
+		snprintf(p, maxlen, "unknown");
+		return;
 	}
  
-	l = strlen(policy_modes[mode]);
-	if (buffer + maxlen < p + l + 1)
-		return -ENOSPC;
+	p += snprintf(p, maxlen, policy_modes[mode]);
  
-	strcpy(p, policy_modes[mode]);
-	p += l;
-
 	if (flags & MPOL_MODE_FLAGS) {
-		if (buffer + maxlen < p + 2)
-			return -ENOSPC;
-		*p++ = '=';
+		p += snprintf(p, buffer + maxlen - p, "=");
  
 		/*
 		 * Currently, the only defined flags are mutually exclusive
  
@@ -2981,11 +2964,8 @@
 	}
  
 	if (!nodes_empty(nodes)) {
-		if (buffer + maxlen < p + 2)
-			return -ENOSPC;
-		*p++ = ':';
+		p += snprintf(p, buffer + maxlen - p, ":");
 	 	p += nodelist_scnprintf(p, buffer + maxlen - p, nodes);
 	}
-	return p - buffer;
 }
...	...	@@ -1387,8 +1387,8 @@
1387	1387	struct mm_struct *mm = vma->vm_mm;
1388	1388	struct mm_walk walk = {};
1389	1389	struct mempolicy *pol;
1390		- int n;
1391		- char buffer[50];
	1390	+ char buffer[64];
	1391	+ int nid;
1392	1392
1393	1393	if (!mm)
1394	1394	return 0;
1395	1395
...	...	@@ -1404,10 +1404,8 @@
1404	1404	walk.mm = mm;
1405	1405
1406	1406	pol = get_vma_policy(task, vma, vma->vm_start);
1407		- n = mpol_to_str(buffer, sizeof(buffer), pol);
	1407	+ mpol_to_str(buffer, sizeof(buffer), pol);
1408	1408	mpol_cond_put(pol);
1409		- if (n < 0)
1410		- return n;
1411	1409
1412	1410	seq_printf(m, "%08lx %s", vma->vm_start, buffer);
1413	1411
...	...	@@ -1460,9 +1458,9 @@
1460	1458	if (md->writeback)
1461	1459	seq_printf(m, " writeback=%lu", md->writeback);
1462	1460
1463		- for_each_node_state(n, N_MEMORY)
1464		- if (md->node[n])
1465		- seq_printf(m, " N%d=%lu", n, md->node[n]);
	1461	+ for_each_node_state(nid, N_MEMORY)
	1462	+ if (md->node[nid])
	1463	+ seq_printf(m, " N%d=%lu", nid, md->node[nid]);
1466	1464	out:
1467	1465	seq_putc(m, '\n');
1468	1466
...	...	@@ -169,7 +169,7 @@
169	169	extern int mpol_parse_str(char str, struct mempolicy *mpol);
170	170	#endif
171	171
172		-extern int mpol_to_str(char buffer, int maxlen, struct mempolicy pol);
	172	+extern void mpol_to_str(char buffer, int maxlen, struct mempolicy pol);
173	173
174	174	/* Check if a vma is migratable */
175	175	static inline int vma_migratable(struct vm_area_struct *vma)
176	176
...	...	@@ -307,9 +307,8 @@
307	307	}
308	308	#endif
309	309
310		-static inline int mpol_to_str(char buffer, int maxlen, struct mempolicy pol)
	310	+static inline void mpol_to_str(char buffer, int maxlen, struct mempolicy pol)
311	311	{
312		- return 0;
313	312	}
314	313
315	314	static inline int mpol_misplaced(struct page page, struct vm_area_struct vma,
...	...	@@ -2914,62 +2914,45 @@
2914	2914	* @maxlen: length of @buffer
2915	2915	* @pol: pointer to mempolicy to be formatted
2916	2916	*
2917		- * Convert a mempolicy into a string.
2918		- * Returns the number of characters in buffer (if positive)
2919		- * or an error (negative)
	2917	+ * Convert @pol into a string. If @buffer is too short, truncate the string.
	2918	+ * Recommend a @maxlen of at least 32 for the longest mode, "interleave", the
	2919	+ * longest flag, "relative", and to display at least a few node ids.
2920	2920	*/
2921		-int mpol_to_str(char buffer, int maxlen, struct mempolicy pol)
	2921	+void mpol_to_str(char buffer, int maxlen, struct mempolicy pol)
2922	2922	{
2923	2923	char *p = buffer;
2924		- int l;
2925		- nodemask_t nodes;
2926		- unsigned short mode;
2927		- unsigned short flags = pol ? pol->flags : 0;
	2924	+ nodemask_t nodes = NODE_MASK_NONE;
	2925	+ unsigned short mode = MPOL_DEFAULT;
	2926	+ unsigned short flags = 0;
2928	2927
2929		- /*
2930		- * Sanity check: room for longest mode, flag and some nodes
2931		- */
2932		- VM_BUG_ON(maxlen < strlen("interleave") + strlen("relative") + 16);
2933		-
2934		- if (!pol \|\| pol == &default_policy)
2935		- mode = MPOL_DEFAULT;
2936		- else
	2928	+ if (pol && pol != &default_policy) {
2937	2929	mode = pol->mode;
	2930	+ flags = pol->flags;
	2931	+ }
2938	2932
2939	2933	switch (mode) {
2940	2934	case MPOL_DEFAULT:
2941		- nodes_clear(nodes);
2942	2935	break;
2943		-
2944	2936	case MPOL_PREFERRED:
2945		- nodes_clear(nodes);
2946	2937	if (flags & MPOL_F_LOCAL)
2947	2938	mode = MPOL_LOCAL;
2948	2939	else
2949	2940	node_set(pol->v.preferred_node, nodes);
2950	2941	break;
2951		-
2952	2942	case MPOL_BIND:
2953		- /* Fall through */
2954	2943	case MPOL_INTERLEAVE:
2955	2944	nodes = pol->v.nodes;
2956	2945	break;
2957		-
2958	2946	default:
2959		- return -EINVAL;
	2947	+ WARN_ON_ONCE(1);
	2948	+ snprintf(p, maxlen, "unknown");
	2949	+ return;
2960	2950	}
2961	2951
2962		- l = strlen(policy_modes[mode]);
2963		- if (buffer + maxlen < p + l + 1)
2964		- return -ENOSPC;
	2952	+ p += snprintf(p, maxlen, policy_modes[mode]);
2965	2953
2966		- strcpy(p, policy_modes[mode]);
2967		- p += l;
2968		-
2969	2954	if (flags & MPOL_MODE_FLAGS) {
2970		- if (buffer + maxlen < p + 2)
2971		- return -ENOSPC;
2972		- *p++ = '=';
	2955	+ p += snprintf(p, buffer + maxlen - p, "=");
2973	2956
2974	2957	/*
2975	2958	* Currently, the only defined flags are mutually exclusive
2976	2959
...	...	@@ -2981,11 +2964,8 @@
2981	2964	}
2982	2965
2983	2966	if (!nodes_empty(nodes)) {
2984		- if (buffer + maxlen < p + 2)
2985		- return -ENOSPC;
2986		- *p++ = ':';
	2967	+ p += snprintf(p, buffer + maxlen - p, ":");
2987	2968	p += nodelist_scnprintf(p, buffer + maxlen - p, nodes);
2988	2969	}
2989		- return p - buffer;
2990	2970	}