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.

Reported-by: syzbot+90b8e10515ae88228a92@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: OGAWA Hirofumi hirofumi@mail.parknet.co.jp ---

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

diff -puN fs/fat/inode.c~fat-fix-kmalloc-failure fs/fat/inode.c --- linux/fs/fat/inode.c~fat-fix-kmalloc-failure 2018-07-12 12:20:30.388600735 +0900 +++ linux-hirofumi/fs/fat/inode.c 2018-07-12 15:09:48.764070539 +0900 @@ -703,13 +703,21 @@ static void fat_set_state(struct super_b 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); }

@@ -1124,7 +1132,7 @@ static int parse_options(struct super_bl 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; @@ -1281,8 +1289,7 @@ static int parse_options(struct super_bl

/* 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; @@ -1873,8 +1880,7 @@ out_fail: 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; _