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Deepanshu Kartikey 9b203b8ddd romfs: check sb_set_blocksize() return value 
[ Upstream commit ab7ad7abb3 ]

romfs_fill_super() ignores the return value of sb_set_blocksize(), which
can fail if the requested block size is incompatible with the block
device's configuration.

This can be triggered by setting a loop device's block size larger than
PAGE_SIZE using ioctl(LOOP_SET_BLOCK_SIZE, 32768), then mounting a romfs
filesystem on that device.

When sb_set_blocksize(sb, ROMBSIZE) is called with ROMBSIZE=4096 but the
device has logical_block_size=32768, bdev_validate_blocksize() fails
because the requested size is smaller than the device's logical block
size. sb_set_blocksize() returns 0 (failure), but romfs ignores this and
continues mounting.

The superblock's block size remains at the device's logical block size
(32768). Later, when sb_bread() attempts I/O with this oversized block
size, it triggers a kernel BUG in folio_set_bh():

    kernel BUG at fs/buffer.c:1582!
    BUG_ON(size > PAGE_SIZE);

Fix by checking the return value of sb_set_blocksize() and failing the
mount with -EINVAL if it returns 0.

Reported-by: syzbot+9c4e33e12283d9437c25@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9c4e33e12283d9437c25
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Link: https://patch.msgid.link/20260113084037.1167887-1-kartikey406@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-02-19 16:29:52 +01:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.