klibc - Jan 2019 - [klibc:update-dash] expand: Fix buffer overflow in expandmeta

Commit-ID:  7154953196c34e244e0e32e73b82ec6a6c29c4e5
Gitweb:    
http://git.kernel.org/?p=libs/klibc/klibc.git;a=commit;h=7154953196c34e244e0e32e73b82ec6a6c29c4e5
Author:     Herbert Xu <herbert at gondor.apana.org.au>
AuthorDate: Sun, 25 Mar 2018 16:38:00 +0800
Committer:  Ben Hutchings <ben at decadent.org.uk>
CommitDate: Fri, 25 Jan 2019 02:57:21 +0000

[klibc] expand: Fix buffer overflow in expandmeta

The native version of expandmeta allocates a buffer that may be
overrun for two reasons.  First of all the size is 1 byte too small
but this is normally hidden because the minimum size is rounded
up to 2048 bytes.  Secondly, if the directory level is deep enough,
any buffer can be overrun.

This patch fixes both problems by calling realloc when necessary.

Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>

---
 usr/dash/expand.c | 57 ++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 33 insertions(+), 24 deletions(-)

diff --git a/usr/dash/expand.c b/usr/dash/expand.c
index 974a31de..f52f34c9 100644
--- a/usr/dash/expand.c
+++ b/usr/dash/expand.c
@@ -124,7 +124,7 @@ STATIC void expandmeta(struct strlist *, int);
 #ifdef HAVE_GLOB
 STATIC void addglob(const glob_t *);
 #else
-STATIC void expmeta(char *, char *);
+STATIC void expmeta(char *, unsigned, unsigned);
 STATIC struct strlist *expsort(struct strlist *);
 STATIC struct strlist *msort(struct strlist *, int);
 #endif
@@ -1246,6 +1246,7 @@ addglob(pglob)
 
 #else	/* HAVE_GLOB */
 STATIC char *expdir;
+STATIC unsigned expdir_max;
 
 
 STATIC void
@@ -1260,6 +1261,7 @@ expandmeta(struct strlist *str, int flag)
 		struct strlist **savelastp;
 		struct strlist *sp;
 		char *p;
+		unsigned len;
 
 		if (fflag)
 			goto nometa;
@@ -1269,12 +1271,11 @@ expandmeta(struct strlist *str, int flag)
 
 		INTOFF;
 		p = preglob(str->text, RMESCAPE_ALLOC | RMESCAPE_HEAP);
-		{
-			int i = strlen(str->text);
-			expdir = ckmalloc(i < 2048 ? 2048 : i); /* XXX */
-		}
+		len = strlen(p);
+		expdir_max = len + PATH_MAX;
+		expdir = ckmalloc(expdir_max);
 
-		expmeta(expdir, p);
+		expmeta(p, len, 0);
 		ckfree(expdir);
 		if (p != str->text)
 			ckfree(p);
@@ -1304,8 +1305,9 @@ nometa:
  */
 
 STATIC void
-expmeta(char *enddir, char *name)
+expmeta(char *name, unsigned name_len, unsigned expdir_len)
 {
+	char *enddir = expdir + expdir_len;
 	char *p;
 	const char *cp;
 	char *start;
@@ -1348,15 +1350,15 @@ expmeta(char *enddir, char *name)
 		}
 	}
 	if (metaflag == 0) {	/* we've reached the end of the file name */
-		if (enddir != expdir)
-			metaflag++;
+		if (!expdir_len)
+			return;
 		p = name;
 		do {
 			if (*p == '\\')
 				p++;
 			*enddir++ = *p;
 		} while (*p++);
-		if (metaflag == 0 || lstat64(expdir, &statb) >= 0)
+		if (lstat64(expdir, &statb) >= 0)
 			addfname(expdir);
 		return;
 	}
@@ -1369,18 +1371,13 @@ expmeta(char *enddir, char *name)
 			*enddir++ = *p++;
 		} while (p < start);
 	}
-	if (enddir == expdir) {
+	*enddir = 0;
+	cp = expdir;
+	expdir_len = enddir - cp;
+	if (!expdir_len)
 		cp = ".";
-	} else if (enddir == expdir + 1 && *expdir == '/') {
-		cp = "/";
-	} else {
-		cp = expdir;
-		enddir[-1] = '\0';
-	}
 	if ((dirp = opendir(cp)) == NULL)
 		return;
-	if (enddir != expdir)
-		enddir[-1] = '/';
 	if (*endname == 0) {
 		atend = 1;
 	} else {
@@ -1388,6 +1385,7 @@ expmeta(char *enddir, char *name)
 		*endname = '\0';
 		endname += esc + 1;
 	}
+	name_len -= endname - name;
 	matchdot = 0;
 	p = start;
 	if (*p == '\\')
@@ -1402,11 +1400,22 @@ expmeta(char *enddir, char *name)
 				scopy(dp->d_name, enddir);
 				addfname(expdir);
 			} else {
-				for (p = enddir, cp = dp->d_name;
-				     (*p++ = *cp++) != '\0';)
-					continue;
-				p[-1] = '/';
-				expmeta(p, endname);
+				unsigned offset;
+				unsigned len;
+
+				p = stpcpy(enddir, dp->d_name);
+				*p = '/';
+
+				offset = p - expdir + 1;
+				len = offset + name_len + NAME_MAX;
+				if (len > expdir_max) {
+					len += PATH_MAX;
+					expdir = ckrealloc(expdir, len);
+					expdir_max = len;
+				}
+
+				expmeta(endname, name_len, offset);
+				enddir = expdir + expdir_len;
 			}
 		}
 	}