From: Eric Biggers <ebiggers@kernel.org>
To: Yongpeng Yang <yangyongpeng.storage@gmail.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>, Theodore Ts'o <tytso@mit.edu>,
linux-fscrypt@vger.kernel.org,
Yongpeng Yang <yangyongpeng@xiaomi.com>
Subject: Re: [PATCH] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT
Date: Wed, 29 Oct 2025 09:48:10 -0700 [thread overview]
Message-ID: <20251029164810.GB1603@sol> (raw)
In-Reply-To: <20251029130608.331477-1-yangyongpeng.storage@gmail.com>
On Wed, Oct 29, 2025 at 09:06:08PM +0800, Yongpeng Yang wrote:
> From: Yongpeng Yang <yangyongpeng@xiaomi.com>
>
> When simulating an nvme device on qemu with both logical_block_size and
> physical_block_size set to 8 KiB, a error trace appears during partition
> table reading at boot time. The issue is caused by inode->i_blkbits being
> larger than PAGE_SHIFT, which leads to a left shift of -1 and triggering a
> UBSAN warning.
>
> [ 2.697306] ------------[ cut here ]------------
> [ 2.697309] UBSAN: shift-out-of-bounds in fs/crypto/inline_crypt.c:336:37
> [ 2.697311] shift exponent -1 is negative
> [ 2.697315] CPU: 3 UID: 0 PID: 274 Comm: (udev-worker) Not tainted 6.18.0-rc2+ #34 PREEMPT(voluntary)
> [ 2.697317] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
> [ 2.697320] Call Trace:
> [ 2.697324] <TASK>
> [ 2.697325] dump_stack_lvl+0x76/0xa0
> [ 2.697340] dump_stack+0x10/0x20
> [ 2.697342] __ubsan_handle_shift_out_of_bounds+0x1e3/0x390
> [ 2.697351] bh_get_inode_and_lblk_num.cold+0x12/0x94
> [ 2.697359] fscrypt_set_bio_crypt_ctx_bh+0x44/0x90
> [ 2.697365] submit_bh_wbc+0xb6/0x190
> [ 2.697370] block_read_full_folio+0x194/0x270
> [ 2.697371] ? __pfx_blkdev_get_block+0x10/0x10
> [ 2.697375] ? __pfx_blkdev_read_folio+0x10/0x10
> [ 2.697377] blkdev_read_folio+0x18/0x30
> [ 2.697379] filemap_read_folio+0x40/0xe0
> [ 2.697382] filemap_get_pages+0x5ef/0x7a0
> [ 2.697385] ? mmap_region+0x63/0xd0
> [ 2.697389] filemap_read+0x11d/0x520
> [ 2.697392] blkdev_read_iter+0x7c/0x180
> [ 2.697393] vfs_read+0x261/0x390
> [ 2.697397] ksys_read+0x71/0xf0
> [ 2.697398] __x64_sys_read+0x19/0x30
> [ 2.697399] x64_sys_call+0x1e88/0x26a0
> [ 2.697405] do_syscall_64+0x80/0x670
> [ 2.697410] ? __x64_sys_newfstat+0x15/0x20
> [ 2.697414] ? x64_sys_call+0x204a/0x26a0
> [ 2.697415] ? do_syscall_64+0xb8/0x670
> [ 2.697417] ? irqentry_exit_to_user_mode+0x2e/0x2a0
> [ 2.697420] ? irqentry_exit+0x43/0x50
> [ 2.697421] ? exc_page_fault+0x90/0x1b0
> [ 2.697422] entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [ 2.697425] RIP: 0033:0x75054cba4a06
> [ 2.697426] Code: 5d e8 41 8b 93 08 03 00 00 59 5e 48 83 f8 fc 75 19 83 e2 39 83 fa 08 75 11 e8 26 ff ff ff 66 0f 1f 44 00 00 48 8b 45 10 0f 05 <48> 8b 5d f8 c9 c3 0f 1f 40 00 f3 0f 1e fa 55 48 89 e5 48 83 ec 08
> [ 2.697427] RSP: 002b:00007fff973723a0 EFLAGS: 00000202 ORIG_RAX: 0000000000000000
> [ 2.697430] RAX: ffffffffffffffda RBX: 00005ea9a2c02760 RCX: 000075054cba4a06
> [ 2.697432] RDX: 0000000000002000 RSI: 000075054c190000 RDI: 000000000000001b
> [ 2.697433] RBP: 00007fff973723c0 R08: 0000000000000000 R09: 0000000000000000
> [ 2.697434] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
> [ 2.697434] R13: 00005ea9a2c027c0 R14: 00005ea9a2be5608 R15: 00005ea9a2be55f0
> [ 2.697436] </TASK>
> [ 2.697436] ---[ end trace ]---
>
> Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
> ---
> fs/crypto/inline_crypt.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
> index 5dee7c498bc8..6beb5f490612 100644
> --- a/fs/crypto/inline_crypt.c
> +++ b/fs/crypto/inline_crypt.c
> @@ -333,7 +333,7 @@ static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh,
> inode = mapping->host;
>
> *inode_ret = inode;
> - *lblk_num_ret = ((u64)folio->index << (PAGE_SHIFT - inode->i_blkbits)) +
> + *lblk_num_ret = (((u64)folio->index << PAGE_SHIFT) >> inode->i_blkbits) +
> (bh_offset(bh) >> inode->i_blkbits);
> return true;
Looks good, but could you clarify in the commit message that this issue
doesn't occur on an encrypted file but rather a block device inode?
fscrypt_set_bio_crypt_ctx_bh() runs the above code before checking
IS_ENCRYPTED(), so that's why it was reached.
Otherwise the patch seems surprising, since i_blkbits > PAGE_SHIFT isn't
a case that is supported on encrypted files yet at all.
- Eric
next prev parent reply other threads:[~2025-10-29 16:49 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-29 13:06 [PATCH] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT Yongpeng Yang
2025-10-29 16:48 ` Eric Biggers [this message]
2025-10-30 7:03 ` Yongpeng Yang
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