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nilfs2: reject invalid block index in GC ioctl

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Syzbot reported list corruption caused by a double list_add_tail() call on
bh->b_assoc_buffers within nilfs_lookup_dirty_data_buffers().

Analysis revealed that the root cause was the insertion of a page/folio
with a page index of ULONG_MAX into the page cache via the GC ioctl.
filemap_get_folios_tag(), called by nilfs_lookup_dirty_data_buffers(),
repeatedly detects a dirty folio with a page index of ULONG_MAX due to
index wrap-around, leading to duplicate processing of dirty buffers.

As a preparatory step, the GC ioctl loads the page/folio of the block to
be moved during GC and inserts it into the page cache based on information
in the nilfs_vdesc structure passed as an argument.  Normally, this does
not cause issues because the user-space GC library configures the
nilfs_vdesc structure properly.  However, since there is no range check on
the parameters determining the page index, a request with artificially
crafted parameters -- such as those generated by Syzbot -- can result in a
page/folio being inserted with a page index of ULONG_MAX, triggering the
above problem.

This resolves the issue by checking the ranges of 'vd_offset' and
'vd_vblocknr' in the nilfs_vdesc structure that determine the page index,
thereby preventing the invalid page/folio insertions.

Reported-by: syzbot+c37bed40868932d790e9@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c37bed40868932d790e9
Fixes: 7942b919f7 ("nilfs2: ioctl operations")
Cc: wuyankun <wuyankun@uniontech.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
This commit is contained in:
Ryusuke Konishi 2026-07-03 01:07:19 +09:00 • committed by Viacheslav Dubeyko
commit a1735eae55
1 changed files with 18 additions and 2 deletions
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