* [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT
@ 2025-10-30 7:29 Yongpeng Yang
2025-11-03 16:48 ` Eric Biggers
0 siblings, 1 reply; 7+ messages in thread
From: Yongpeng Yang @ 2025-10-30 7:29 UTC (permalink / raw)
To: Eric Biggers, Jaegeuk Kim, Theodore Ts'o; +Cc: linux-fscrypt, Yongpeng Yang
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 ]---
This situation can happen for block devices because when
CONFIG_TRANSPARENT_HUGEPAGE is enabled, the maximum logical_block_size
is 64 KiB. set_init_blocksize() then sets the block device inode->i_blkbits
to 8 KiB, which is within this limit.
File I/O does not trigger this problem because for filesystems that do not
support the FS_LBS feature, sb_set_blocksize() prevents sb->s_blocksize_bits
from being larger than PAGE_SHIFT. During inode allocation,
alloc_inode()->inode_init_always() assigns inode->i_blkbits from
sb->s_blocksize_bits. Currently, only xfs_fs_type has the FS_LBS flag, and
since xfs I/O paths do not reach submit_bh_wbc(), it does not hit the
left-shift underflow issue.
Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
---
v2:
- Added more explanations about the issue in the commit message.
---
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;
}
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT
2025-10-30 7:29 [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT Yongpeng Yang
@ 2025-11-03 16:48 ` Eric Biggers
2025-11-04 11:12 ` Christoph Hellwig
0 siblings, 1 reply; 7+ messages in thread
From: Eric Biggers @ 2025-11-03 16:48 UTC (permalink / raw)
To: Yongpeng Yang
Cc: Jaegeuk Kim, Theodore Ts'o, linux-fscrypt, Yongpeng Yang,
linux-fsdevel, linux-block, Luis Chamberlain
[+linux-fsdevel, linux-block, and Luis]
On Thu, Oct 30, 2025 at 03:29:56PM +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 ]---
>
> This situation can happen for block devices because when
> CONFIG_TRANSPARENT_HUGEPAGE is enabled, the maximum logical_block_size
> is 64 KiB. set_init_blocksize() then sets the block device inode->i_blkbits
> to 8 KiB, which is within this limit.
>
> File I/O does not trigger this problem because for filesystems that do not
> support the FS_LBS feature, sb_set_blocksize() prevents sb->s_blocksize_bits
> from being larger than PAGE_SHIFT. During inode allocation,
> alloc_inode()->inode_init_always() assigns inode->i_blkbits from
> sb->s_blocksize_bits. Currently, only xfs_fs_type has the FS_LBS flag, and
> since xfs I/O paths do not reach submit_bh_wbc(), it does not hit the
> left-shift underflow issue.
>
> Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
> ---
> v2:
> - Added more explanations about the issue in the commit message.
> ---
> 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;
> }
Applied to https://git.kernel.org/pub/scm/fs/fscrypt/linux.git/log/?h=for-current
I also added:
Fixes: 47dd67532303 ("block/bdev: lift block size restrictions to 64k")
Cc: stable@vger.kernel.org
- Eric
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT
2025-11-03 16:48 ` Eric Biggers
@ 2025-11-04 11:12 ` Christoph Hellwig
2025-11-04 15:05 ` Yongpeng Yang
2025-11-04 18:10 ` Eric Biggers
0 siblings, 2 replies; 7+ messages in thread
From: Christoph Hellwig @ 2025-11-04 11:12 UTC (permalink / raw)
To: Eric Biggers
Cc: Yongpeng Yang, Jaegeuk Kim, Theodore Ts'o, linux-fscrypt,
Yongpeng Yang, linux-fsdevel, linux-block, Luis Chamberlain
On Mon, Nov 03, 2025 at 08:48:29AM -0800, Eric Biggers wrote:
> > *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) +
This should be using folio_pos() instead of open coding the arithmetics.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT
2025-11-04 11:12 ` Christoph Hellwig
@ 2025-11-04 15:05 ` Yongpeng Yang
2025-11-05 13:38 ` Christoph Hellwig
2025-11-04 18:10 ` Eric Biggers
1 sibling, 1 reply; 7+ messages in thread
From: Yongpeng Yang @ 2025-11-04 15:05 UTC (permalink / raw)
To: Christoph Hellwig, Eric Biggers
Cc: Jaegeuk Kim, Theodore Ts'o, linux-fscrypt, Yongpeng Yang,
linux-fsdevel, linux-block, Luis Chamberlain
On 11/4/2025 7:12 PM, Christoph Hellwig wrote:
> On Mon, Nov 03, 2025 at 08:48:29AM -0800, Eric Biggers wrote:
>>> *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) +
>
> This should be using folio_pos() instead of open coding the arithmetics.
>
How about this modification: using "<< PAGE_SHIFT" instead of "*
PAGE_SIZE" for page_offset and folio_pos?
--- 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_pos(folio) >> inode->i_blkbits) +
(bh_offset(bh) >> inode->i_blkbits);
return true;
}
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 09b581c1d878..72eeb1841bc3 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1026,7 +1026,7 @@ static inline pgoff_t page_pgoff(const struct
folio *folio,
*/
static inline loff_t folio_pos(const struct folio *folio)
{
- return ((loff_t)folio->index) * PAGE_SIZE;
+ return ((loff_t)folio->index) << PAGE_SHIFT;
}
/*
@@ -1036,7 +1036,7 @@ static inline loff_t page_offset(struct page *page)
{
struct folio *folio = page_folio(page);
- return folio_pos(folio) + folio_page_idx(folio, page) * PAGE_SIZE;
+ return folio_pos(folio) + (folio_page_idx(folio, page) <<
PAGE_SHIFT);
}
Yongpeng,
^ permalink raw reply related [flat|nested] 7+ messages in thread* Re: [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT
2025-11-04 15:05 ` Yongpeng Yang
@ 2025-11-05 13:38 ` Christoph Hellwig
0 siblings, 0 replies; 7+ messages in thread
From: Christoph Hellwig @ 2025-11-05 13:38 UTC (permalink / raw)
To: Yongpeng Yang
Cc: Christoph Hellwig, Eric Biggers, Jaegeuk Kim, Theodore Ts'o,
linux-fscrypt, Yongpeng Yang, linux-fsdevel, linux-block,
Luis Chamberlain
On Tue, Nov 04, 2025 at 11:05:49PM +0800, Yongpeng Yang wrote:
> On 11/4/2025 7:12 PM, Christoph Hellwig wrote:
> > On Mon, Nov 03, 2025 at 08:48:29AM -0800, Eric Biggers wrote:
> > > > *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) +
> >
> > This should be using folio_pos() instead of open coding the arithmetics.
> >
>
> How about this modification: using "<< PAGE_SHIFT" instead of "* PAGE_SIZE"
> for page_offset and folio_pos?
Any decent compiler turns a multiplication by a compіle time fixed
power of two constant in shifts, so why bother?
(and yes, I just double checked this happens here)
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT
2025-11-04 11:12 ` Christoph Hellwig
2025-11-04 15:05 ` Yongpeng Yang
@ 2025-11-04 18:10 ` Eric Biggers
2025-11-05 13:40 ` Christoph Hellwig
1 sibling, 1 reply; 7+ messages in thread
From: Eric Biggers @ 2025-11-04 18:10 UTC (permalink / raw)
To: Christoph Hellwig
Cc: Yongpeng Yang, Jaegeuk Kim, Theodore Ts'o, linux-fscrypt,
Yongpeng Yang, linux-fsdevel, linux-block, Luis Chamberlain
On Tue, Nov 04, 2025 at 03:12:53AM -0800, Christoph Hellwig wrote:
> On Mon, Nov 03, 2025 at 08:48:29AM -0800, Eric Biggers wrote:
> > > *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) +
>
> This should be using folio_pos() instead of open coding the arithmetics.
Well, folio_pos() doesn't work with sizes greater than S64_MAX, and it
uses multiplication rather than a shift.
Probably doesn't matter, but I always feel like I have to actually check
that.
It looks like the size of block device can come from several different
places, including set_capacity(), bdev_resize_partition(), and
add_partition(). The first has a size check. I don't immediately see a
size check in the other two. Maybe it's there and I need to look
closer. Also can the size of a block device be set in other ways?
Then I have to remember whether a multiplication of a signed value gets
reliably optimized to a shift on all architectures or not. I think so.
Anyway, the trivial version avoids having to consider any of this...
- Eric
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT
2025-11-04 18:10 ` Eric Biggers
@ 2025-11-05 13:40 ` Christoph Hellwig
0 siblings, 0 replies; 7+ messages in thread
From: Christoph Hellwig @ 2025-11-05 13:40 UTC (permalink / raw)
To: Eric Biggers
Cc: Christoph Hellwig, Yongpeng Yang, Jaegeuk Kim, Theodore Ts'o,
linux-fscrypt, Yongpeng Yang, linux-fsdevel, linux-block,
Luis Chamberlain
On Tue, Nov 04, 2025 at 10:10:06AM -0800, Eric Biggers wrote:
> On Tue, Nov 04, 2025 at 03:12:53AM -0800, Christoph Hellwig wrote:
> > On Mon, Nov 03, 2025 at 08:48:29AM -0800, Eric Biggers wrote:
> > > > *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) +
> >
> > This should be using folio_pos() instead of open coding the arithmetics.
>
> Well, folio_pos() doesn't work with sizes greater than S64_MAX, and it
> uses multiplication rather than a shift.
What do you mean with "sizes greater than S64_MAX"? folio_pos works
on a folio and is the MM designated helper to get the file offset
from a folio, where a file offset is a loff_t, aka s64.
And as answered to the previous mail, the compiler turns that
multiplication into a shift.
> Anyway, the trivial version avoids having to consider any of this...
I see it the other way around - folio_pos is the defined way to get
the index into the inode (block device inode here) in the abstract
way.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2025-11-05 13:40 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
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2025-10-30 7:29 [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT Yongpeng Yang
2025-11-03 16:48 ` Eric Biggers
2025-11-04 11:12 ` Christoph Hellwig
2025-11-04 15:05 ` Yongpeng Yang
2025-11-05 13:38 ` Christoph Hellwig
2025-11-04 18:10 ` Eric Biggers
2025-11-05 13:40 ` Christoph Hellwig
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