From: Theodore Ts'o tytso@mit.edu

commit 9803387c55f7d2ce69aa64340c5fdc6b3027dbc8 upstream.

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.

Link: https://lore.kernel.org/r/20191215063020.GA11512@mit.edu Cc: stable@kernel.org Signed-off-by: Theodore Ts'o tytso@mit.edu Reported-and-tested-by: syzbot+4a39a025912b265cacef@syzkaller.appspotmail.com Signed-off-by: Zubin Mithra zsm@chromium.org --- Notes: * Syzkaller triggered a UAF on 4.19 kernels with the following stacktrace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0xc8/0x129 lib/dump_stack.c:113 print_address_description+0x67/0x22a mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report mm/kasan/report.c:412 [inline] kasan_report+0x251/0x28f mm/kasan/report.c:396 ext4_xattr_set_entry+0x45e/0x2222 fs/ext4/xattr.c:1604 ext4_xattr_ibody_set+0x7d/0x226 fs/ext4/xattr.c:2240 ext4_xattr_set_handle+0x553/0xa92 fs/ext4/xattr.c:2396 ext4_xattr_set+0x16a/0x200 fs/ext4/xattr.c:2508 __vfs_setxattr+0xfc/0x13d fs/xattr.c:149 __vfs_setxattr_noperm+0xf5/0x19c fs/xattr.c:180 vfs_setxattr+0x9c/0xca fs/xattr.c:223 setxattr+0x20e/0x275 fs/xattr.c:450 path_setxattr+0xca/0x144 fs/xattr.c:469 __do_sys_lsetxattr fs/xattr.c:491 [inline] __se_sys_lsetxattr fs/xattr.c:487 [inline] __x64_sys_lsetxattr+0xd7/0xe1 fs/xattr.c:487 do_syscall_64+0xfe/0x137 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe

* This commit is present in linux-5.4.y. A backport for 4.14.y has been sent separately.

* This patch resolves conflicts related to the following commits not being present in linux-4.19.y: 188d20bcd1eb ("vfs: Add file timestamp range support") 4881c4971df0 ("ext4: Initialize timestamps limits")

* Tests run: Chrome OS tryjobs, Syzkaller reproducer

fs/ext4/super.c | 127 +++++++++++++++++++++++++----------------------- 1 file changed, 66 insertions(+), 61 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 1a8d57fe0b1a8..32d8bdf683bbf 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1842,6 +1842,13 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token, arg = JBD2_DEFAULT_MAX_COMMIT_AGE; 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; @@ -3513,40 +3520,6 @@ 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; @@ -3754,6 +3727,65 @@ 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; + } else { + sb->s_time_gran = NSEC_PER_SEC; + } + } + 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), @@ -3955,29 +3987,6 @@ 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; - } - if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE) - sb->s_time_gran = 1 << (EXT4_EPOCH_BITS - 2); - } - 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 || @@ -4421,8 +4430,6 @@ 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); @@ -5207,8 +5214,6 @@ 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 "