* [PATCH 1/2] hfs: fall back to buffered I/O for direct writes past phys_size
2026-10-30 4:29 [PATCH 0/2] hfs: fall back to buffered I/O for direct writes past phys_size Hengyu Liang
@ 2026-10-30 4:29 ` Hengyu Liang
2026-10-30 4:29 ` [PATCH 2/2] hfs: remove the dead grow path from hfs_file_truncate() Hengyu Liang
2026-10-31 8:59 ` [syzbot ci] Re: hfs: fall back to buffered I/O for direct writes past phys_size syzbot ci
2 siblings, 0 replies; 4+ messages in thread
From: Hengyu Liang @ 2026-10-30 4:29 UTC (permalink / raw)
To: slava; +Cc: glaubitz, frank.li, linux-fsdevel, linux-kernel
hfs_direct_IO() passes direct writes to blockdev_direct_IO(), which
does not go through hfs_write_begin(). When such a write needs a new
block, hfs_get_block() only adds the block size to phys_size. phys_size
starts at i_size when the inode is read, which does not have to be
block aligned, so after the write phys_size is smaller than i_size.
However, at the last close, hfs_file_truncate() sees i_size larger than
phys_size and calls hfs_write_begin() at i_size, which zeroes the file
from phys_size up to i_size. As of now, part of the data that a direct
write has just written past the old end of the file is lost, and fsck
reports no error.
The issue can be reproduced with:
truncate -s 32M hfs.img
mkfs.hfsplus -h hfs.img
mount -t hfs -o loop hfs.img /mnt
printf 'A%.0s' $(seq 100) > /mnt/f
umount /mnt
mount -t hfs -o loop hfs.img /mnt
xfs_io -d -c 'pwrite -S 0x42 512 512' /mnt/f
umount /mnt
mount -t hfs -o loop hfs.img /mnt
od -An -tx1 -j 512 -N 512 /mnt/f
The last 412 bytes read back as zeros instead of 0x42.
This patch will make a direct write that ends past phys_size fall back
to a buffered write, as fat_direct_IO() and affs_direct_IO() do.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Hengyu Liang <hengyul@cs.unc.edu>
---
fs/hfs/inode.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c
index d9abab2a1e61..d476a16f4ef9 100644
--- a/fs/hfs/inode.c
+++ b/fs/hfs/inode.c
@@ -139,6 +139,16 @@ static ssize_t hfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
size_t count = iov_iter_count(iter);
ssize_t ret;
+ /*
+ * blockdev_direct_IO() does not go through ->write_begin(), so it
+ * neither zeroes the file from phys_size up to the write nor keeps
+ * phys_size in step with i_size. Return 0 for a write that ends
+ * past phys_size, so that it falls back to a buffered write.
+ */
+ if (iov_iter_rw(iter) == WRITE &&
+ iocb->ki_pos + count > HFS_I(inode)->phys_size)
+ return 0;
+
ret = blockdev_direct_IO(iocb, inode, iter, hfs_get_block);
/*
--
2.53.0
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH 2/2] hfs: remove the dead grow path from hfs_file_truncate()
2026-10-30 4:29 [PATCH 0/2] hfs: fall back to buffered I/O for direct writes past phys_size Hengyu Liang
2026-10-30 4:29 ` [PATCH 1/2] " Hengyu Liang
@ 2026-10-30 4:29 ` Hengyu Liang
2026-10-31 8:59 ` [syzbot ci] Re: hfs: fall back to buffered I/O for direct writes past phys_size syzbot ci
2 siblings, 0 replies; 4+ messages in thread
From: Hengyu Liang @ 2026-10-30 4:29 UTC (permalink / raw)
To: slava; +Cc: glaubitz, frank.li, linux-fsdevel, linux-kernel
hfs_file_truncate() grows the file through hfs_write_begin() when
i_size is larger than phys_size. That case no longer happens.
phys_size is set to i_size when the inode is read. After that, i_size
only grows through hfs_write_begin(), which grows phys_size first, or
through a direct write that ends within phys_size.
"hfs: report errors when extending files with setattr" made
hfs_inode_setattr() extend files with generic_cont_expand_simple(),
and "hfs: fall back to buffered I/O for direct writes past phys_size"
made direct writes past phys_size go through hfs_write_begin() too.
This patch removes the grow path, and warns and returns if i_size is
ever larger than phys_size.
Suggested-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Hengyu Liang <hengyul@cs.unc.edu>
---
fs/hfs/extent.c | 18 ++----------------
1 file changed, 2 insertions(+), 16 deletions(-)
diff --git a/fs/hfs/extent.c b/fs/hfs/extent.c
index 26357086517f..8d04b7c0911e 100644
--- a/fs/hfs/extent.c
+++ b/fs/hfs/extent.c
@@ -491,23 +491,9 @@ void hfs_file_truncate(struct inode *inode)
hfs_dbg("ino %llu, phys_size %llu -> i_size %llu\n",
inode->i_ino, (long long)HFS_I(inode)->phys_size,
inode->i_size);
- if (inode->i_size > HFS_I(inode)->phys_size) {
- struct address_space *mapping = inode->i_mapping;
- void *fsdata = NULL;
- struct folio *folio;
-
- /* XXX: Can use generic_cont_expand? */
- size = inode->i_size - 1;
- res = hfs_write_begin(NULL, mapping, size + 1, 0, &folio,
- &fsdata);
- if (!res) {
- res = generic_write_end(NULL, mapping, size + 1, 0, 0,
- folio, fsdata);
- }
- if (res)
- inode->i_size = HFS_I(inode)->phys_size;
+ if (WARN_ON_ONCE(inode->i_size > HFS_I(inode)->phys_size))
return;
- } else if (inode->i_size == HFS_I(inode)->phys_size)
+ if (inode->i_size == HFS_I(inode)->phys_size)
return;
size = inode->i_size + HFS_SB(sb)->alloc_blksz - 1;
blk_cnt = size / HFS_SB(sb)->alloc_blksz;
--
2.53.0
^ permalink raw reply [flat|nested] 4+ messages in thread* [syzbot ci] Re: hfs: fall back to buffered I/O for direct writes past phys_size
2026-10-30 4:29 [PATCH 0/2] hfs: fall back to buffered I/O for direct writes past phys_size Hengyu Liang
2026-10-30 4:29 ` [PATCH 1/2] " Hengyu Liang
2026-10-30 4:29 ` [PATCH 2/2] hfs: remove the dead grow path from hfs_file_truncate() Hengyu Liang
@ 2026-10-31 8:59 ` syzbot ci
2 siblings, 0 replies; 4+ messages in thread
From: syzbot ci @ 2026-10-31 8:59 UTC (permalink / raw)
To: frank.li, glaubitz, hengyul, linux-fsdevel, linux-kernel, slava
Cc: syzbot, syzkaller-bugs
syzbot ci has tested the following series
[v1] hfs: fall back to buffered I/O for direct writes past phys_size
https://lore.kernel.org/all/20261030042903.4160506-1-hengyul@cs.unc.edu
* [PATCH 1/2] hfs: fall back to buffered I/O for direct writes past phys_size
* [PATCH 2/2] hfs: remove the dead grow path from hfs_file_truncate()
and found the following issue:
WARNING in hfs_file_truncate
Full report is available here:
https://ci.syzbot.org/series/f8323fc4-a62a-40ea-9106-bff8391323a3
***
WARNING in hfs_file_truncate
tree: axboe
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/axboe/linux.git
base: a804c5742bff224d4cb4d25dd383554d598be32b
arch: amd64
compiler: Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
config: https://ci.syzbot.org/builds/734131df-1170-4dc7-a0ec-85ffb659aeec/config
syz repro: https://ci.syzbot.org/findings/95638e3e-6c06-4f46-a68b-e468dc287d1e/syz_repro
------------[ cut here ]------------
inode->i_size > HFS_I(inode)->phys_size
WARNING: fs/hfs/extent.c:494 at hfs_file_truncate+0x7cf/0xa50 fs/hfs/extent.c:494, CPU#1: syz.2.19/5839
Modules linked in:
CPU: 1 UID: 0 PID: 5839 Comm: syz.2.19 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:hfs_file_truncate+0x7cf/0xa50 fs/hfs/extent.c:494
Code: 8b 05 ed eb db 11 48 3b 84 24 20 01 00 00 75 1f 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d e9 88 09 33 09 cc e8 02 10 0b ff 90 <0f> 0b 90 eb 9b e8 67 00 30 09 44 89 e9 80 e1 07 80 c1 03 38 c1 0f
RSP: 0018:ffffc900034afaa0 EFLAGS: 00010293
RAX: ffffffff82bca45e RBX: 1ffff92000695f68 RCX: ffff88810ca50000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000852
RBP: ffffc900034afc08 R08: ffffc900034afb97 R09: 0000000000000000
R10: ffffc900034afb60 R11: fffff52000695f73 R12: 0000000000000000
R13: ffff88816b59b100 R14: dffffc0000000000 R15: 0000000000000852
FS: 00007f4cc5ac36c0(0000) GS:ffff8882a7c97000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000560c8ef2a008 CR3: 00000001bd922000 CR4: 00000000000006f0
Call Trace:
<TASK>
hfs_inode_setattr+0x4d0/0x730 fs/hfs/inode.c:698
notify_change+0xbba/0xea0 fs/attr.c:556
do_truncate+0x1c2/0x250 fs/open.c:68
do_ftruncate+0x4d4/0x580 fs/open.c:194
ksys_ftruncate fs/open.c:206 [inline]
__do_sys_ftruncate fs/open.c:211 [inline]
__se_sys_ftruncate fs/open.c:209 [inline]
__x64_sys_ftruncate+0x8f/0xe0 fs/open.c:209
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4cc4b9f559
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f4cc5ac3028 EFLAGS: 00000246 ORIG_RAX: 000000000000004d
RAX: ffffffffffffffda RBX: 00007f4cc4e25fa0 RCX: 00007f4cc4b9f559
RDX: 0000000000000000 RSI: 0000000000000852 RDI: 0000000000000004
RBP: 00007f4cc4c36b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4cc4e26038 R14: 00007f4cc4e25fa0 R15: 00007ffcf07cc2c8
</TASK>
***
If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syzbot@syzkaller.appspotmail.com
---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.
To test a fix for this bug, please reply with `#syz test`
(on a separate line) and attach the patch to the email.
Notes:
- The patch will be applied on top of the tested series (as an
incremental fix).
- To test a new version of the whole series, please send it directly
to syzbot@lists.linux.dev.
- Arguments like custom git repos and branches are not supported.
^ permalink raw reply [flat|nested] 4+ messages in thread