commit e24ba8b6c403f8c706a9aa0dd64050c2449a9fca
Author: Kristof Provost <kristof@codepro.be>
Date:   Sun Mar 13 06:14:51 2016 +0100

    msdosfs: Prevent buffer overflow when expanding win95 names
    
    In win2unixfn() we expand Windows 95 style long names. In some cases that
    requires moving the data in the nbp->nb_buf buffer backwards to make room. That
    code failed to check for overflows, leading to a stack overflow in win2unixfn().
    
    We now check for this event, and mark the entire conversion as failed in that
    case. This means we present the 8 character, dos style, name instead.
    
    PR:	204643

diff --git a/sys/fs/msdosfs/direntry.h b/sys/fs/msdosfs/direntry.h
index 86b6fbb..facec30 100644
--- a/sys/fs/msdosfs/direntry.h
+++ b/sys/fs/msdosfs/direntry.h
@@ -145,7 +145,7 @@ struct msdosfsmount;
 
 char	*mbnambuf_flush(struct mbnambuf *nbp, struct dirent *dp);
 void	mbnambuf_init(struct mbnambuf *nbp);
-void	mbnambuf_write(struct mbnambuf *nbp, char *name, int id);
+int	mbnambuf_write(struct mbnambuf *nbp, char *name, int id);
 int	dos2unixfn(u_char dn[11], u_char *un, int lower,
 	    struct msdosfsmount *pmp);
 int	unix2dosfn(const u_char *un, u_char dn[12], size_t unlen, u_int gen,
diff --git a/sys/fs/msdosfs/msdosfs_conv.c b/sys/fs/msdosfs/msdosfs_conv.c
index fc9b4d4..e584d69 100644
--- a/sys/fs/msdosfs/msdosfs_conv.c
+++ b/sys/fs/msdosfs/msdosfs_conv.c
@@ -634,6 +634,7 @@ win2unixfn(struct mbnambuf *nbp, struct winentry *wep, int chksum,
 	u_int8_t *np, name[WIN_CHARS * 3 + 1];
 	u_int16_t code;
 	int i;
+	int ret;
 
 	if ((wep->weCnt&WIN_CNT) > howmany(WIN_MAXLEN, WIN_CHARS)
 	    || !(wep->weCnt&WIN_CNT))
@@ -658,7 +659,9 @@ win2unixfn(struct mbnambuf *nbp, struct winentry *wep, int chksum,
 		switch (code) {
 		case 0:
 			*np = '\0';
-			mbnambuf_write(nbp, name, (wep->weCnt & WIN_CNT) - 1);
+			ret = mbnambuf_write(nbp, name, (wep->weCnt & WIN_CNT) - 1);
+			if (ret < 0)
+				return (-1);
 			return chksum;
 		case '/':
 			*np = '\0';
@@ -676,7 +679,9 @@ win2unixfn(struct mbnambuf *nbp, struct winentry *wep, int chksum,
 		switch (code) {
 		case 0:
 			*np = '\0';
-			mbnambuf_write(nbp, name, (wep->weCnt & WIN_CNT) - 1);
+			ret = mbnambuf_write(nbp, name, (wep->weCnt & WIN_CNT) - 1);
+			if (ret < 0)
+				return (-1);
 			return chksum;
 		case '/':
 			*np = '\0';
@@ -694,7 +699,9 @@ win2unixfn(struct mbnambuf *nbp, struct winentry *wep, int chksum,
 		switch (code) {
 		case 0:
 			*np = '\0';
-			mbnambuf_write(nbp, name, (wep->weCnt & WIN_CNT) - 1);
+			ret = mbnambuf_write(nbp, name, (wep->weCnt & WIN_CNT) - 1);
+			if (ret < 0)
+				return (-1);
 			return chksum;
 		case '/':
 			*np = '\0';
@@ -708,7 +715,9 @@ win2unixfn(struct mbnambuf *nbp, struct winentry *wep, int chksum,
 		cp += 2;
 	}
 	*np = '\0';
-	mbnambuf_write(nbp, name, (wep->weCnt & WIN_CNT) - 1);
+	ret = mbnambuf_write(nbp, name, (wep->weCnt & WIN_CNT) - 1);
+	if (ret < 0)
+		return (-1);
 	return chksum;
 }
 
@@ -1005,7 +1014,7 @@ mbnambuf_init(struct mbnambuf *nbp)
  * This only penalizes portions of substrings that contain more than
  * WIN_CHARS bytes when they are first encountered.
  */
-void
+int
 mbnambuf_write(struct mbnambuf *nbp, char *name, int id)
 {
 	char *slot;
@@ -1016,7 +1025,7 @@ mbnambuf_write(struct mbnambuf *nbp, char *name, int id)
 		printf("msdosfs: non-decreasing id: id %d, last id %d\n",
 		    id, nbp->nb_last_id);
 #endif
-		return;
+		return (-EINVAL);
 	}
 
 	/* Will store this substring in a WIN_CHARS-aligned slot. */
@@ -1027,17 +1036,24 @@ mbnambuf_write(struct mbnambuf *nbp, char *name, int id)
 #ifdef MSDOSFS_DEBUG
 		printf("msdosfs: file name length %zu too large\n", newlen);
 #endif
-		return;
+		return (-ENOMEM);
 	}
 
 	/* Shift suffix upwards by the amount length exceeds WIN_CHARS. */
 	if (count > WIN_CHARS && nbp->nb_len != 0)
+	{
+		if (((slot - nbp->nb_buf) + count + nbp->nb_len) > sizeof(nbp->nb_buf))
+			return (-ENOMEM);
+
 		bcopy(slot + WIN_CHARS, slot + count, nbp->nb_len);
+	}
 
 	/* Copy in the substring to its slot and update length so far. */
 	bcopy(name, slot, count);
 	nbp->nb_len = newlen;
 	nbp->nb_last_id = id;
+
+	return (0);
 }
 
 /*