From 35033ab988c396ad7bce3b6d24060c16a9066db8 Mon Sep 17 00:00:00 2001
From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Date: Fri, 20 Jul 2018 17:53:42 -0700
Subject: [PATCH] fat: fix memory allocation failure handling of match_strdup()
Git-commit: 35033ab988c396ad7bce3b6d24060c16a9066db8
Patch-mainline: v4.18-rc6
References: bsc#1051510

In parse_options(), if match_strdup() failed, parse_options() leaves
opts->iocharset in unexpected state (i.e.  still pointing the freed
string).  And this can be the cause of double free.

To fix, this initialize opts->iocharset always when freeing.

Link: http://lkml.kernel.org/r/8736wp9dzc.fsf@mail.parknet.co.jp
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Reported-by: syzbot+90b8e10515ae88228a92@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 fs/fat/inode.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 065dc919a0ce..bfd589ea74c0 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -707,13 +707,21 @@ static void fat_set_state(struct super_block *sb,
 	brelse(bh);
 }
 
+static void fat_reset_iocharset(struct fat_mount_options *opts)
+{
+	if (opts->iocharset != fat_default_iocharset) {
+		/* Note: opts->iocharset can be NULL here */
+		kfree(opts->iocharset);
+		opts->iocharset = fat_default_iocharset;
+	}
+}
+
 static void delayed_free(struct rcu_head *p)
 {
 	struct msdos_sb_info *sbi = container_of(p, struct msdos_sb_info, rcu);
 	unload_nls(sbi->nls_disk);
 	unload_nls(sbi->nls_io);
-	if (sbi->options.iocharset != fat_default_iocharset)
-		kfree(sbi->options.iocharset);
+	fat_reset_iocharset(&sbi->options);
 	kfree(sbi);
 }
 
@@ -1132,7 +1140,7 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
 	opts->fs_fmask = opts->fs_dmask = current_umask();
 	opts->allow_utime = -1;
 	opts->codepage = fat_default_codepage;
-	opts->iocharset = fat_default_iocharset;
+	fat_reset_iocharset(opts);
 	if (is_vfat) {
 		opts->shortname = VFAT_SFN_DISPLAY_WINNT|VFAT_SFN_CREATE_WIN95;
 		opts->rodir = 0;
@@ -1289,8 +1297,7 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
 
 		/* vfat specific */
 		case Opt_charset:
-			if (opts->iocharset != fat_default_iocharset)
-				kfree(opts->iocharset);
+			fat_reset_iocharset(opts);
 			iocharset = match_strdup(&args[0]);
 			if (!iocharset)
 				return -ENOMEM;
@@ -1881,8 +1888,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
 		iput(fat_inode);
 	unload_nls(sbi->nls_io);
 	unload_nls(sbi->nls_disk);
-	if (sbi->options.iocharset != fat_default_iocharset)
-		kfree(sbi->options.iocharset);
+	fat_reset_iocharset(&sbi->options);
 	sb->s_fs_info = NULL;
 	kfree(sbi);
 	return error;
-- 
2.18.0