Tito writes:

Hi,
I've spent the half night staring at the devilish  my_getpwuid and my_getgrgid functions
trying to find out a way to avoid actual and future potential buffer overflow problems
without breaking existing code.
Finally I've  found a not intrusive way to do this that surely doesn't break existing code
and fixes a couple of problems too.
The attached patch:
1) changes the behaviour of my_getpwuid and my_getgrgid to avoid potetntial buffer overflows
2) fixes all occurences of this function calls in tar.c , id.c , ls.c, whoami.c, logger.c, libbb.h.
3) The behaviour of tar, ls and  logger is unchanged.
4) The behavior of ps with somewhat longer usernames messing up output is fixed.
5) The only bigger change was the increasing of size of the buffers in id.c to avoid
     false negatives (unknown user: xxxxxx) with usernames longer than 8 chars.
     The value i used ( 32 chars ) was taken from the tar header ( see gname and uname).
     Maybe this buffers can be reduced a bit  ( to 16 or whatever ), this is up to you.
6) The increase of size of the binary is not so dramatic:
     size busybox
       text    data     bss     dec     hex filename
     239568    2300   36816  278684   4409c busybox
    size busybox_fixed
       text    data     bss     dec     hex filename
     239616    2300   36816  278732   440cc busybox
7) The behaviour of whoami changed:
    actually it  prints out an username cut down to the size of the buffer.
    This could be fixed by increasing the size of the buffer as in id.c or
    avoid the use of my_getpwuid and use getpwuid directly instead.
    Maybe this colud be also remain unchanged......

Please apply if you think it is ok to do so.
The diff applies on today's cvs tarball (2004-08-25).
Thanks in advance,
Ciao,
Tito

archival/tar.c

@@ -234,9 +234,9 @@ static inline int writeTarHeader(struct TarBallInfo *tbInfo,
 			TAR_MAGIC_LEN + TAR_VERSION_LEN);
 
 	/* Enter the user and group names (default to root if it fails) */
-	if (my_getpwuid(header.uname, statbuf->st_uid) == NULL)
+	if (my_getpwuid(header.uname, statbuf->st_uid, sizeof(header.uname)) == NULL)
 		strcpy(header.uname, "root");
-	if (my_getgrgid(header.gname, statbuf->st_gid) == NULL)
+	if (my_getgrgid(header.gname, statbuf->st_gid, sizeof(header.gname)) == NULL)
 		strcpy(header.gname, "root");
 
 	if (tbInfo->hlInfo) {

coreutils/id.c

@@ -40,7 +40,7 @@
 
 extern int id_main(int argc, char **argv)
 {
-	char user[9], group[9];
+	char user[32], group[32];
 	long pwnam, grnam;
 	int uid, gid;
 	int flags;
@@ -64,12 +64,12 @@ extern int id_main(int argc, char **argv)
 			uid = geteuid();
 			gid = getegid();
 		}
-		my_getpwuid(user, uid);
+		my_getpwuid(user, uid, sizeof(user));
 	} else {
 		safe_strncpy(user, argv[optind], sizeof(user));
 	    gid = my_getpwnamegid(user);
 	}
-	my_getgrgid(group, gid);
+	my_getgrgid(group, gid, sizeof(group));
 
 	pwnam=my_getpwnam(user);
 	grnam=my_getgrnam(group);

coreutils/ls.c

@@ -683,9 +683,9 @@ static int list_single(struct dnode *dn)
 			break;
 		case LIST_ID_NAME:
 #ifdef CONFIG_FEATURE_LS_USERNAME
-			my_getpwuid(scratch, dn->dstat.st_uid);
+			my_getpwuid(scratch, dn->dstat.st_uid, sizeof(scratch));
 			printf("%-8.8s ", scratch);
-			my_getgrgid(scratch, dn->dstat.st_gid);
+			my_getgrgid(scratch, dn->dstat.st_gid, sizeof(scratch));
 			printf("%-8.8s", scratch);
 			column += 17;
 			break;

coreutils/whoami.c

@@ -36,7 +36,7 @@ extern int whoami_main(int argc, char **argv)
 		bb_show_usage();
 
 	uid = geteuid();
-	if (my_getpwuid(user, uid)) {
+	if (my_getpwuid(user, uid, sizeof(user))) {
 		puts(user);
 		bb_fflush_stdout_and_exit(EXIT_SUCCESS);
 	}

include/libbb.h

@@ -230,8 +230,8 @@ extern unsigned long bb_xparse_number(const char *numstr,
  * increases target size and is often not needed embedded systems.  */
 extern long my_getpwnam(const char *name);
 extern long my_getgrnam(const char *name);
-extern char * my_getpwuid(char *name, long uid);
+extern char * my_getpwuid(char *name, long uid, int bufsize);
-extern char * my_getgrgid(char *group, long gid);
+extern char * my_getgrgid(char *group, long gid, int bufsize);
 extern long my_getpwnamegid(const char *name);
 extern char *bb_askpass(int timeout, const char * prompt);
 

libbb/my_getgrgid.c

@@ -27,16 +27,16 @@
 
 
 /* gets a groupname given a gid */
-char * my_getgrgid(char *group, long gid)
+char * my_getgrgid(char *group, long gid, int bufsize)
 {
 	struct group *mygroup;
 
 	mygroup  = getgrgid(gid);
 	if (mygroup==NULL) {
-		sprintf(group, "%ld", gid);
+		snprintf(group, bufsize, "%ld", gid);
 		return NULL;
 	} else {
-		return strcpy(group, mygroup->gr_name);
+		return safe_strncpy(group, mygroup->gr_name, bufsize);
 	}
 }
 

libbb/my_getpwuid.c

@@ -28,16 +28,16 @@
 
 
 /* gets a username given a uid */
-char * my_getpwuid(char *name, long uid)
+char * my_getpwuid(char *name, long uid, int bufsize)
 {
 	struct passwd *myuser;
 
 	myuser  = getpwuid(uid);
 	if (myuser==NULL) {
-		sprintf(name, "%ld", (long)uid);
+		snprintf(name, bufsize, "%ld", (long)uid);
 		return NULL;
 	} else {
-		return strcpy(name, myuser->pw_name);
+		return safe_strncpy(name, myuser->pw_name, bufsize);
 	}
 }
 

libbb/procps.c

@@ -57,7 +57,7 @@ extern procps_status_t * procps_scan(int save_user_arg0
 		sprintf(status, "/proc/%d", pid);
 		if(stat(status, &sb))
 			continue;
-		my_getpwuid(curstatus.user, sb.st_uid);
+		my_getpwuid(curstatus.user, sb.st_uid, sizeof(curstatus.user));
 
 		sprintf(status, "/proc/%d/stat", pid);
 		if((fp = fopen(status, "r")) == NULL)

sysklogd/logger.c

@@ -108,7 +108,7 @@ extern int logger_main(int argc, char **argv)
 	char buf[1024], name[128];
 
 	/* Fill out the name string early (may be overwritten later) */
-	my_getpwuid(name, geteuid());
+	my_getpwuid(name, geteuid(), sizeof(name));
 
 	/* Parse any options */
 	while ((opt = getopt(argc, argv, "p:st:")) > 0) {