On Tue, Dec 08, 2020 at 11:33:11PM -0800, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 15ac8fdb Add linux-next specific files for 20201207 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=1125c923500000 > kernel config: https://syzkaller.appspot.com/x/.config?x=3696b8138207d24d > dashboard link: https://syzkaller.appspot.com/bug?extid=345b75652b1d24227443 > compiler: gcc (GCC) 10.1.0-syz 20200507 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=151bf86b500000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=139212cb500000 #syz test git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git e360ba58d067a30a4e3e7d55ebdd919885a058d6 >From 3d3bc303a8a8f7123cf486f49fa9060116fa1465 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o <tytso@xxxxxxx> Date: Wed, 9 Dec 2020 15:59:11 -0500 Subject: [PATCH] ext4: check for invalid block size early when mounting a file system Check for valid block size directly by validating s_log_block_size; we were doing this in two places. First, by calculating blocksize via BLOCK_SIZE << s_log_block_size, and then checking that the blocksize was valid. And then secondly, by checking s_log_block_size directly. The first check is not reliable, and can trigger an UBSAN warning if s_log_block_size on a maliciously corrupted superblock is greater than 22. This is harmless, since the second test will correctly reject the maliciously fuzzed file system, but to make syzbot shut up, and because the two checks are duplicative in any case, delete the blocksize check, and move the s_log_block_size earlier in ext4_fill_super(). Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> Reported-by: syzbot+345b75652b1d24227443@xxxxxxxxxxxxxxxxxxxxxxxxx --- fs/ext4/super.c | 40 ++++++++++++++++------------------------ 1 file changed, 16 insertions(+), 24 deletions(-) diff --git a/fs/ext4/super.c b/fs/ext4/super.c index f86220a8df50..4a16bbf0432c 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -4202,18 +4202,25 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent) */ sbi->s_li_wait_mult = EXT4_DEF_LI_WAIT_MULT; - blocksize = BLOCK_SIZE << le32_to_cpu(es->s_log_block_size); - - if (blocksize == PAGE_SIZE) - set_opt(sb, DIOREAD_NOLOCK); - - if (blocksize < EXT4_MIN_BLOCK_SIZE || - blocksize > EXT4_MAX_BLOCK_SIZE) { + if (le32_to_cpu(es->s_log_block_size) > + (EXT4_MAX_BLOCK_LOG_SIZE - EXT4_MIN_BLOCK_LOG_SIZE)) { ext4_msg(sb, KERN_ERR, - "Unsupported filesystem blocksize %d (%d log_block_size)", - blocksize, le32_to_cpu(es->s_log_block_size)); + "Invalid log block size: %u", + le32_to_cpu(es->s_log_block_size)); goto failed_mount; } + if (le32_to_cpu(es->s_log_cluster_size) > + (EXT4_MAX_CLUSTER_LOG_SIZE - EXT4_MIN_BLOCK_LOG_SIZE)) { + ext4_msg(sb, KERN_ERR, + "Invalid log cluster size: %u", + le32_to_cpu(es->s_log_cluster_size)); + goto failed_mount; + } + + blocksize = EXT4_MIN_BLOCK_SIZE << le32_to_cpu(es->s_log_block_size); + + if (blocksize == PAGE_SIZE) + set_opt(sb, DIOREAD_NOLOCK); if (le32_to_cpu(es->s_rev_level) == EXT4_GOOD_OLD_REV) { sbi->s_inode_size = EXT4_GOOD_OLD_INODE_SIZE; @@ -4432,21 +4439,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent) if (!ext4_feature_set_ok(sb, (sb_rdonly(sb)))) goto failed_mount; - if (le32_to_cpu(es->s_log_block_size) > - (EXT4_MAX_BLOCK_LOG_SIZE - EXT4_MIN_BLOCK_LOG_SIZE)) { - ext4_msg(sb, KERN_ERR, - "Invalid log block size: %u", - le32_to_cpu(es->s_log_block_size)); - goto failed_mount; - } - if (le32_to_cpu(es->s_log_cluster_size) > - (EXT4_MAX_CLUSTER_LOG_SIZE - EXT4_MIN_BLOCK_LOG_SIZE)) { - ext4_msg(sb, KERN_ERR, - "Invalid log cluster size: %u", - le32_to_cpu(es->s_log_cluster_size)); - goto failed_mount; - } - if (le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) > (blocksize / 4)) { ext4_msg(sb, KERN_ERR, "Number of reserved GDT blocks insanely large: %d", -- 2.28.0
