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Date: Mon, 16 Dec 2019 09:09:51 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: "Theodore Y. Ts'o" <tytso@....edu>
Cc: syzbot <syzbot+4a39a025912b265cacef@...kaller.appspotmail.com>,
a@...table.cc, Andreas Dilger <adilger.kernel@...ger.ca>,
afd@...com, b.a.t.m.a.n@...ts.open-mesh.org, chris@...a.com.au,
David Miller <davem@...emloft.net>, linux-ext4@...r.kernel.org,
LKML <linux-kernel@...r.kernel.org>, mareklindner@...mailbox.ch,
netdev <netdev@...r.kernel.org>,
Pali Rohár <pali.rohar@...il.com>,
sre@...nel.org, sw@...onwunderlich.de,
syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: use-after-free Read in ext4_xattr_set_entry (2)
On Sun, Dec 15, 2019 at 7:30 AM Theodore Y. Ts'o <tytso@....edu> wrote:
>
> On Sat, Dec 14, 2019 at 05:27:00PM -0800, syzbot wrote:
> > syzbot has bisected this bug to:
> >
> > commit 8835cae5f2abd7f7a3143afe357f416aff5517a4
> > Author: Chris Lapa <chris@...a.com.au>
> > Date: Wed Jan 11 01:44:47 2017 +0000
> >
> > power: supply: bq27xxx: adds specific support for bq27520-g4 revision.
>
> This is pretty clearly nonsense.
Agree.
FTR, it seems that bisection was first diverged by this kernel bug:
testing commit 8835cae5f2abd7f7a3143afe357f416aff5517a4 with gcc (GCC) 5.5.0
run #0: crashed: WARNING in batadv_mcast_mla_update
on top of this non-deterministic kernel build bug kicked in to prevent
detection of "culprit does not affect build":
culprit signature: 2aca06cd9a4175f124f866fe66467cfa96c0bf2a
parent signature: 8a8dd9ca5726f129b6d36eb6e1f3b78cc7c18b31
> However let's try this fix:
>
> #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git master
>
> From 9c962de70a52e0b24fba00ee7b8707964d3d1e37 Mon Sep 17 00:00:00 2001
> From: Theodore Ts'o <tytso@....edu>
> Date: Sun, 15 Dec 2019 01:09:03 -0500
> Subject: [PATCH] ext4: validate the debug_want_extra_isize mount option at parse time
>
> Instead of setting s_want_extra_size and then making sure that it is a
> valid value afterwards, validate the field before we set it. This
> avoids races and other problems when remounting the file system.
>
> Signed-off-by: Theodore Ts'o <tytso@....edu>
> Reported-by: syzbot+4a39a025912b265cacef@...kaller.appspotmail.com
> ---
> fs/ext4/super.c | 143 +++++++++++++++++++++++-------------------------
> 1 file changed, 69 insertions(+), 74 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index b205112ca051..46b6d5b150ac 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1886,6 +1886,13 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
> }
> sbi->s_commit_interval = HZ * arg;
> } else if (token == Opt_debug_want_extra_isize) {
> + if ((arg & 1) ||
> + (arg < 4) ||
> + (arg > (sbi->s_inode_size - EXT4_GOOD_OLD_INODE_SIZE))) {
> + ext4_msg(sb, KERN_ERR,
> + "Invalid want_extra_isize %d", arg);
> + return -1;
> + }
> sbi->s_want_extra_isize = arg;
> } else if (token == Opt_max_batch_time) {
> sbi->s_max_batch_time = arg;
> @@ -3540,40 +3547,6 @@ 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;
> - unsigned def_extra_isize = sizeof(struct ext4_inode) -
> - EXT4_GOOD_OLD_INODE_SIZE;
> -
> - if (sbi->s_inode_size == EXT4_GOOD_OLD_INODE_SIZE) {
> - sbi->s_want_extra_isize = 0;
> - return;
> - }
> - if (sbi->s_want_extra_isize < 4) {
> - sbi->s_want_extra_isize = def_extra_isize;
> - 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 ((sbi->s_want_extra_isize > sbi->s_inode_size) ||
> - (EXT4_GOOD_OLD_INODE_SIZE + sbi->s_want_extra_isize >
> - sbi->s_inode_size)) {
> - sbi->s_want_extra_isize = def_extra_isize;
> - 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;
> @@ -3781,6 +3754,68 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> */
> sbi->s_li_wait_mult = EXT4_DEF_LI_WAIT_MULT;
>
> + if (le32_to_cpu(es->s_rev_level) == EXT4_GOOD_OLD_REV) {
> + sbi->s_inode_size = EXT4_GOOD_OLD_INODE_SIZE;
> + sbi->s_first_ino = EXT4_GOOD_OLD_FIRST_INO;
> + } else {
> + sbi->s_inode_size = le16_to_cpu(es->s_inode_size);
> + sbi->s_first_ino = le32_to_cpu(es->s_first_ino);
> + if (sbi->s_first_ino < EXT4_GOOD_OLD_FIRST_INO) {
> + ext4_msg(sb, KERN_ERR, "invalid first ino: %u",
> + sbi->s_first_ino);
> + goto failed_mount;
> + }
> + if ((sbi->s_inode_size < EXT4_GOOD_OLD_INODE_SIZE) ||
> + (!is_power_of_2(sbi->s_inode_size)) ||
> + (sbi->s_inode_size > blocksize)) {
> + ext4_msg(sb, KERN_ERR,
> + "unsupported inode size: %d",
> + sbi->s_inode_size);
> + goto failed_mount;
> + }
> + /*
> + * i_atime_extra is the last extra field available for
> + * [acm]times in struct ext4_inode. Checking for that
> + * field should suffice to ensure we have extra space
> + * for all three.
> + */
> + if (sbi->s_inode_size >= offsetof(struct ext4_inode, i_atime_extra) +
> + sizeof(((struct ext4_inode *)0)->i_atime_extra)) {
> + sb->s_time_gran = 1;
> + sb->s_time_max = EXT4_EXTRA_TIMESTAMP_MAX;
> + } else {
> + sb->s_time_gran = NSEC_PER_SEC;
> + sb->s_time_max = EXT4_NON_EXTRA_TIMESTAMP_MAX;
> + }
> + sb->s_time_min = EXT4_TIMESTAMP_MIN;
> + }
> + if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE) {
> + sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
> + EXT4_GOOD_OLD_INODE_SIZE;
> + if (ext4_has_feature_extra_isize(sb)) {
> + unsigned v, max = (sbi->s_inode_size -
> + EXT4_GOOD_OLD_INODE_SIZE);
> +
> + v = le16_to_cpu(es->s_want_extra_isize);
> + if (v > max) {
> + ext4_msg(sb, KERN_ERR,
> + "bad s_want_extra_isize: %d", v);
> + goto failed_mount;
> + }
> + if (sbi->s_want_extra_isize < v)
> + sbi->s_want_extra_isize = v;
> +
> + v = le16_to_cpu(es->s_min_extra_isize);
> + if (v > max) {
> + ext4_msg(sb, KERN_ERR,
> + "bad s_min_extra_isize: %d", v);
> + goto failed_mount;
> + }
> + if (sbi->s_want_extra_isize < v)
> + sbi->s_want_extra_isize = v;
> + }
> + }
> +
> if (sbi->s_es->s_mount_opts[0]) {
> char *s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
> sizeof(sbi->s_es->s_mount_opts),
> @@ -4019,42 +4054,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> has_huge_files);
> sb->s_maxbytes = ext4_max_size(sb->s_blocksize_bits, has_huge_files);
>
> - if (le32_to_cpu(es->s_rev_level) == EXT4_GOOD_OLD_REV) {
> - sbi->s_inode_size = EXT4_GOOD_OLD_INODE_SIZE;
> - sbi->s_first_ino = EXT4_GOOD_OLD_FIRST_INO;
> - } else {
> - sbi->s_inode_size = le16_to_cpu(es->s_inode_size);
> - sbi->s_first_ino = le32_to_cpu(es->s_first_ino);
> - if (sbi->s_first_ino < EXT4_GOOD_OLD_FIRST_INO) {
> - ext4_msg(sb, KERN_ERR, "invalid first ino: %u",
> - sbi->s_first_ino);
> - goto failed_mount;
> - }
> - if ((sbi->s_inode_size < EXT4_GOOD_OLD_INODE_SIZE) ||
> - (!is_power_of_2(sbi->s_inode_size)) ||
> - (sbi->s_inode_size > blocksize)) {
> - ext4_msg(sb, KERN_ERR,
> - "unsupported inode size: %d",
> - sbi->s_inode_size);
> - goto failed_mount;
> - }
> - /*
> - * i_atime_extra is the last extra field available for [acm]times in
> - * struct ext4_inode. Checking for that field should suffice to ensure
> - * we have extra space for all three.
> - */
> - if (sbi->s_inode_size >= offsetof(struct ext4_inode, i_atime_extra) +
> - sizeof(((struct ext4_inode *)0)->i_atime_extra)) {
> - sb->s_time_gran = 1;
> - sb->s_time_max = EXT4_EXTRA_TIMESTAMP_MAX;
> - } else {
> - sb->s_time_gran = NSEC_PER_SEC;
> - sb->s_time_max = EXT4_NON_EXTRA_TIMESTAMP_MAX;
> - }
> -
> - sb->s_time_min = EXT4_TIMESTAMP_MIN;
> - }
> -
> sbi->s_desc_size = le16_to_cpu(es->s_desc_size);
> if (ext4_has_feature_64bit(sb)) {
> if (sbi->s_desc_size < EXT4_MIN_DESC_SIZE_64BIT ||
> @@ -4503,8 +4502,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> } else if (ret)
> goto failed_mount4a;
>
> - ext4_clamp_want_extra_isize(sb);
> -
> ext4_set_resv_clusters(sb);
>
> err = ext4_setup_system_zone(sb);
> @@ -5292,8 +5289,6 @@ 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 "
> --
> 2.24.1
>
> --
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