tools/mm: fix slabinfo crash when MAX_SLABS is exceeded

The number of slabs can easily exceed the hard coded MAX_SLABS in the
slabinfo tool, causing it to overwrite memory and crash.

Increase the value of MAX_SLABS, and check if that has been exceeded for
each new slab, instead of at the end when it's already too late.  Also
move the check for MAX_ALIASES into the loop body.

Link: https://lkml.kernel.org/r/20241031105534.565533-1-marc.c.dionne@gmail.com
Signed-off-by: Marc Dionne <marc.dionne@auristor.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Marc Dionne

tools/mm/slabinfo.c

@@ -21,7 +21,7 @@
 #include <regex.h>
 #include <errno.h>
 
-#define MAX_SLABS 500
+#define MAX_SLABS 2000
 #define MAX_ALIASES 500
 #define MAX_NODES 1024
 
@@ -1228,6 +1228,8 @@ static void read_slab_dir(void)
 				continue;
 		switch (de->d_type) {
 		   case DT_LNK:
+			if (alias - aliasinfo == MAX_ALIASES)
+				fatal("Too many aliases\n");
 			alias->name = strdup(de->d_name);
 			count = readlink(de->d_name, buffer, sizeof(buffer)-1);
 
@@ -1242,6 +1244,8 @@ static void read_slab_dir(void)
 			alias++;
 			break;
 		   case DT_DIR:
+			if (slab - slabinfo == MAX_SLABS)
+				fatal("Too many slabs\n");
 			if (chdir(de->d_name))
 				fatal("Unable to access slab %s\n", slab->name);
 			slab->name = strdup(de->d_name);
@@ -1312,10 +1316,6 @@ static void read_slab_dir(void)
 	slabs = slab - slabinfo;
 	actual_slabs = slabs;
 	aliases = alias - aliasinfo;
-	if (slabs > MAX_SLABS)
-		fatal("Too many slabs\n");
-	if (aliases > MAX_ALIASES)
-		fatal("Too many aliases\n");
 }
 
 static void output_slabs(void)