fix a race when fetching files from the kernel. the number of files

might have increased between when we got the number of files and
when we requested that number of files.

now we allocate another 10ish percent on top of what the kernel
says we need, and retry if that still isnt enough.

while here use realloc instead of constantly going through free/malloc
sequences.

with input from claudio@ deraadt@
ok millert@ guenther@

1 files changed, 41 insertions, 36 deletions

diff --git a/lib/libkvm/kvm_file2.c b/lib/libkvm/kvm_file2.c
index 04912bf2562..669a7d4ae77 100644
--- a/lib/libkvm/kvm_file2.c
+++ b/lib/libkvm/kvm_file2.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kvm_file2.c,v 1.46 2015/08/28 04:38:47 guenther Exp $	*/
+/*	$OpenBSD: kvm_file2.c,v 1.47 2015/09/04 02:58:14 dlg Exp $	*/
 
 /*
  * Copyright (c) 2009 Todd C. Miller <Todd.Miller@courtesan.com>
@@ -114,6 +114,7 @@
 #include <string.h>
 #include <unistd.h>
 #include <limits.h>
+#include <errno.h>
 
 #include "kvm_private.h"
 #include "kvm_file.h"
@@ -132,44 +133,46 @@ struct kinfo_file *
 kvm_getfiles(kvm_t *kd, int op, int arg, size_t esize, int *cnt)
 {
 	int mib[6], rv;
+	void *filebase;
 	size_t size;
 
-	if (kd->filebase != NULL) {
-		free(kd->filebase);
-		/*
-		 * Clear this pointer in case this call fails.  Otherwise,
-		 * kvm_close() will free it again.
-		 */
-		kd->filebase = 0;
-	}
-
 	if (ISALIVE(kd)) {
 		mib[0] = CTL_KERN;
 		mib[1] = KERN_FILE;
 		mib[2] = op;
 		mib[3] = arg;
 		mib[4] = esize;
-		mib[5] = 0;
-
-		/* find size and alloc buffer */
-		rv = sysctl(mib, 6, NULL, &size, NULL, 0);
-		if (rv == -1) {
-			if (kd->vmfd != -1)
-				goto deadway;
-			_kvm_syserr(kd, kd->program, "kvm_getfiles");
-			return (NULL);
-		}
-		kd->filebase = _kvm_malloc(kd, size);
-		if (kd->filebase == NULL)
-			return (NULL);
 
-		/* get actual data */
-		mib[5] = size / esize;
-		rv = sysctl(mib, 6, kd->filebase, &size, NULL, 0);
-		if (rv == -1) {
-			_kvm_syserr(kd, kd->program, "kvm_getfiles");
-			return (NULL);
-		}
+		do {
+			mib[5] = 0;
+
+			/* find size and alloc buffer */
+			rv = sysctl(mib, 6, NULL, &size, NULL, 0);
+			if (rv == -1) {
+				if (kd->vmfd != -1)
+					goto deadway;
+				_kvm_syserr(kd, kd->program, "kvm_getfiles");
+				return (NULL);
+			}
+
+			size += size / 8; /* add ~10% */
+
+			filebase = _kvm_realloc(kd, kd->filebase, size);
+			if (filebase == NULL)
+				return (NULL);
+
+			kd->filebase = filebase;
+
+			/* get actual data */
+			mib[5] = size / esize;
+			rv = sysctl(mib, 6, kd->filebase, &size, NULL, 0);
+			if (rv == -1 && errno != ENOMEM) {
+				_kvm_syserr(kd, kd->program,
+				    "kvm_getfiles");
+				return (NULL);
+			}
+		} while (rv == -1);
+
 		*cnt = size / esize;
 		return (kd->filebase);
 	} else {
@@ -224,10 +227,11 @@ kvm_deadfile_byfile(kvm_t *kd, int op, int arg, size_t esize, int *cnt)
 		_kvm_err(kd, kd->program, "can't read nfiles");
 		return (NULL);
 	}
-	where = _kvm_reallocarray(kd, NULL, nfiles, esize);
-	kd->filebase = (void *)where;
-	if (kd->filebase == NULL)
+	where = _kvm_reallocarray(kd, kd->filebase, nfiles, esize);
+	if (where == NULL)
 		return (NULL);
+
+	kd->filebase = (void *)where;
 	buflen = nfiles * esize;
 
 	for (fp = LIST_FIRST(&filehead);
@@ -301,10 +305,11 @@ kvm_deadfile_byid(kvm_t *kd, int op, int arg, size_t esize, int *cnt)
 		return (NULL);
 	}
 	/* this may be more room than we need but counting is expensive */
-	where = _kvm_reallocarray(kd, NULL, nfiles + 10, esize);
-	kd->filebase = (void *)where;
-	if (kd->filebase == NULL)
+	where = _kvm_reallocarray(kd, kd->filebase, nfiles + 10, esize);
+	if (where == NULL)
 		return (NULL);
+
+	kd->filebase = (void *)where;
 	buflen = (nfiles + 10) * esize;
 
 	for (pr = LIST_FIRST(&allprocess);