linux-kernel - [PATCH v3] vfat: don't read garbage after last dirent

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Date:   Fri,  1 Feb 2019 01:14:08 +0100
From:   Matteo Croce <mcroce@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Timothy Redaelli <tredaelli@...hat.com>
Subject: [PATCH v3] vfat: don't read garbage after last dirent

The FAT32 File System Specification[1] states that:

    If DIR_Name[0] == 0x00, then the directory entry is free, and there
    are no allocated directory entries after this one.

    The special 0 value, indicates to FAT file system driver code that
    the rest of the entries in this directory do not need to be examined
    because they are all free.

This is not enforced by Linux, and is possible to read garbage if not
all dirents after the last one are filled with zeroes.

[1] http://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/fatgen103.doc

Reported-by: Timothy Redaelli <tredaelli@...hat.com>
Signed-off-by: Matteo Croce <mcroce@...hat.com>
---
 fs/fat/dir.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index 9d01db37183f..d919a1ee519c 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -314,7 +314,7 @@ static int fat_parse_long(struct inode *dir, loff_t *pos,
 
 		if (ds->id & 0x40)
 			(*unicode)[offset + 13] = 0;
-		if (fat_get_entry(dir, pos, bh, de) < 0)
+		if (fat_get_entry(dir, pos, bh, de) < 0 || !(*de)->name[0])
 			return PARSE_EOF;
 		if (slot == 0)
 			break;
@@ -476,7 +476,8 @@ int fat_search_long(struct inode *inode, const unsigned char *name,
 
 	err = -ENOENT;
 	while (1) {
-		if (fat_get_entry(inode, &cpos, &bh, &de) == -1)
+		if (fat_get_entry(inode, &cpos, &bh, &de) == -1 ||
+		    !de->name[0])
 			goto end_of_dir;
 parse_record:
 		nr_slots = 0;
@@ -588,7 +589,7 @@ static int __fat_readdir(struct inode *inode, struct file *file,
 
 	bh = NULL;
 get_new:
-	if (fat_get_entry(inode, &cpos, &bh, &de) == -1)
+	if (fat_get_entry(inode, &cpos, &bh, &de) == -1 || !de->name[0])
 		goto end_of_dir;
 parse_record:
 	nr_slots = 0;
@@ -898,7 +899,8 @@ int fat_get_dotdot_entry(struct inode *dir, struct buffer_head **bh,
 	loff_t offset = 0;
 
 	*de = NULL;
-	while (fat_get_short_entry(dir, &offset, bh, de) >= 0) {
+	while (fat_get_short_entry(dir, &offset, bh, de) >= 0 &&
+	       (*de)->name[0]) {
 		if (!strncmp((*de)->name, MSDOS_DOTDOT, MSDOS_NAME))
 			return 0;
 	}
@@ -916,7 +918,8 @@ int fat_dir_empty(struct inode *dir)
 
 	bh = NULL;
 	cpos = 0;
-	while (fat_get_short_entry(dir, &cpos, &bh, &de) >= 0) {
+	while (fat_get_short_entry(dir, &cpos, &bh, &de) >= 0 &&
+	       de->name[0]) {
 		if (strncmp(de->name, MSDOS_DOT   , MSDOS_NAME) &&
 		    strncmp(de->name, MSDOS_DOTDOT, MSDOS_NAME)) {
 			result = -ENOTEMPTY;
@@ -941,7 +944,8 @@ int fat_subdirs(struct inode *dir)
 
 	bh = NULL;
 	cpos = 0;
-	while (fat_get_short_entry(dir, &cpos, &bh, &de) >= 0) {
+	while (fat_get_short_entry(dir, &cpos, &bh, &de) >= 0 &&
+	       de->name[0]) {
 		if (de->attr & ATTR_DIR)
 			count++;
 	}
@@ -961,7 +965,7 @@ int fat_scan(struct inode *dir, const unsigned char *name,
 	sinfo->slot_off = 0;
 	sinfo->bh = NULL;
 	while (fat_get_short_entry(dir, &sinfo->slot_off, &sinfo->bh,
-				   &sinfo->de) >= 0) {
+				   &sinfo->de) >= 0 && sinfo->de->name[0]) {
 		if (!strncmp(sinfo->de->name, name, MSDOS_NAME)) {
 			sinfo->slot_off -= sizeof(*sinfo->de);
 			sinfo->nr_slots = 1;
@@ -985,7 +989,7 @@ int fat_scan_logstart(struct inode *dir, int i_logstart,
 	sinfo->slot_off = 0;
 	sinfo->bh = NULL;
 	while (fat_get_short_entry(dir, &sinfo->slot_off, &sinfo->bh,
-				   &sinfo->de) >= 0) {
+				   &sinfo->de) >= 0 && sinfo->de->name[0]) {
 		if (fat_get_start(MSDOS_SB(sb), sinfo->de) == i_logstart) {
 			sinfo->slot_off -= sizeof(*sinfo->de);
 			sinfo->nr_slots = 1;
-- 
2.20.1