The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7bc04c5c2cc467c5b40f2b03ba08da174a0d5fa7 Mon Sep 17 00:00:00 2001

From: Barret Rhoden brho@google.com Date: Thu, 25 Apr 2019 11:55:50 -0400 Subject: [PATCH] ext4: fix use-after-free race with debug_want_extra_isize

When remounting with debug_want_extra_isize, we were not performing the same checks that we do during a normal mount. That allowed us to set a value for s_want_extra_isize that reached outside the s_inode_size.

Fixes: e2b911c53584 ("ext4: clean up feature test macros with predicate functions") Reported-by: syzbot+f584efa0ac7213c226b7@syzkaller.appspotmail.com Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Barret Rhoden brho@google.com Signed-off-by: Theodore Ts'o tytso@mit.edu Cc: stable@vger.kernel.org

diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 6ed4eb81e674..184944d4d8d1 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -3513,6 +3513,37 @@ int ext4_calculate_overhead(struct super_block *sb) return 0; }

+static void ext4_clamp_want_extra_isize(struct super_block *sb) +{ + struct ext4_sb_info *sbi = EXT4_SB(sb); + struct ext4_super_block *es = sbi->s_es; + + /* determine the minimum size of new large inodes, if present */ + if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE && + sbi->s_want_extra_isize == 0) { + sbi->s_want_extra_isize = sizeof(struct ext4_inode) - + EXT4_GOOD_OLD_INODE_SIZE; + if (ext4_has_feature_extra_isize(sb)) { + if (sbi->s_want_extra_isize < + le16_to_cpu(es->s_want_extra_isize)) + sbi->s_want_extra_isize = + le16_to_cpu(es->s_want_extra_isize); + if (sbi->s_want_extra_isize < + le16_to_cpu(es->s_min_extra_isize)) + sbi->s_want_extra_isize = + le16_to_cpu(es->s_min_extra_isize); + } + } + /* Check if enough inode space is available */ + if (EXT4_GOOD_OLD_INODE_SIZE + sbi->s_want_extra_isize > + sbi->s_inode_size) { + sbi->s_want_extra_isize = sizeof(struct ext4_inode) - + EXT4_GOOD_OLD_INODE_SIZE; + ext4_msg(sb, KERN_INFO, + "required extra inode space not available"); + } +} + static void ext4_set_resv_clusters(struct super_block *sb) { ext4_fsblk_t resv_clusters; @@ -4387,30 +4418,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent) } else if (ret) goto failed_mount4a;

- /* determine the minimum size of new large inodes, if present */ - if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE && - sbi->s_want_extra_isize == 0) { - sbi->s_want_extra_isize = sizeof(struct ext4_inode) - - EXT4_GOOD_OLD_INODE_SIZE; - if (ext4_has_feature_extra_isize(sb)) { - if (sbi->s_want_extra_isize < - le16_to_cpu(es->s_want_extra_isize)) - sbi->s_want_extra_isize = - le16_to_cpu(es->s_want_extra_isize); - if (sbi->s_want_extra_isize < - le16_to_cpu(es->s_min_extra_isize)) - sbi->s_want_extra_isize = - le16_to_cpu(es->s_min_extra_isize); - } - } - /* Check if enough inode space is available */ - if (EXT4_GOOD_OLD_INODE_SIZE + sbi->s_want_extra_isize > - sbi->s_inode_size) { - sbi->s_want_extra_isize = sizeof(struct ext4_inode) - - EXT4_GOOD_OLD_INODE_SIZE; - ext4_msg(sb, KERN_INFO, "required extra inode space not" - "available"); - } + ext4_clamp_want_extra_isize(sb);

ext4_set_resv_clusters(sb);

@@ -5194,6 +5202,8 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data) goto restore_opts; }

+ ext4_clamp_want_extra_isize(sb); + if ((old_opts.s_mount_opt & EXT4_MOUNT_JOURNAL_CHECKSUM) ^ test_opt(sb, JOURNAL_CHECKSUM)) { ext4_msg(sb, KERN_ERR, "changing journal_checksum "