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Thu, 30 Oct 2025 00:03:46 -0700 (PDT) Message-ID: <04ffcdb5-9d9a-450d-a804-104857f25f15@gmail.com> Date: Thu, 30 Oct 2025 15:03:43 +0800 Precedence: bulk X-Mailing-List: linux-fscrypt@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT To: Eric Biggers , Yongpeng Yang Cc: Jaegeuk Kim , Theodore Ts'o , linux-fscrypt@vger.kernel.org, Yongpeng Yang References: <20251029130608.331477-1-yangyongpeng.storage@gmail.com> <20251029164810.GB1603@sol> Content-Language: en-US From: Yongpeng Yang In-Reply-To: <20251029164810.GB1603@sol> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/30/25 00:48, Eric Biggers wrote: > On Wed, Oct 29, 2025 at 09:06:08PM +0800, Yongpeng Yang wrote: >> From: Yongpeng Yang >> >> 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] >> [ 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] >> [ 2.697436] ---[ end trace ]--- >> >> Signed-off-by: Yongpeng Yang >> --- >> 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. Thanks for the review. I’ll add more explanations in v2. Yongpeng, > > Otherwise the patch seems surprising, since i_blkbits > PAGE_SHIFT isn't > a case that is supported on encrypted files yet at all. > > - Eric