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[BUG] The following script can cause btrfs to crash: $ mount -o compress-force=lzo $DEV /mnt $ dd if=/dev/urandom of=/mnt/foo bs=4k count=1 $ sync The call trace looks like this: general protection fault, probably for non-canonical address 0xe04b37fccce3b000: 0000 [#1] PREEMPT SMP NOPTI CPU: 5 PID: 164 Comm: kworker/u20:3 Not tainted 5.15.0-rc7-custom+ #4 Workqueue: btrfs-delalloc btrfs_work_helper [btrfs] RIP: 0010:__memcpy+0x12/0x20 Call Trace: lzo_compress_pages+0x236/0x540 [btrfs] btrfs_compress_pages+0xaa/0xf0 [btrfs] compress_file_range+0x431/0x8e0 [btrfs] async_cow_start+0x12/0x30 [btrfs] btrfs_work_helper+0xf6/0x3e0 [btrfs] process_one_work+0x294/0x5d0 worker_thread+0x55/0x3c0 kthread+0x140/0x170 ret_from_fork+0x22/0x30 ---[ end trace 63c3c0f131e61982 ]--- [CAUSE] In lzo_compress_pages(), parameter @out_pages is not only an output parameter (for the number of compressed pages), but also an input parameter, as the upper limit of compressed pages we can utilize. In commitd4088803f5("btrfs: subpage: make lzo_compress_pages() compatible"), the refactoring doesn't take @out_pages as an input, thus completely ignoring the limit. And for compress-force case, we could hit incompressible data that compressed size would go beyond the page limit, and cause the above crash. [FIX] Save @out_pages as @max_nr_page, and pass it to lzo_compress_pages(), and check if we're beyond the limit before accessing the pages. Note: this also fixes crash on 32bit architectures that was suspected to be caused by merge of btrfs patches to 5.16-rc1. Reported in https://lore.kernel.org/all/20211104115001.GU20319@twin.jikos.cz/ . Reported-by: Omar Sandoval <osandov@fb.com> Fixes:d4088803f5("btrfs: subpage: make lzo_compress_pages() compatible") Reviewed-by: Omar Sandoval <osandov@fb.com> Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Qu Wenruo <wqu@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> [ add note ] Signed-off-by: David Sterba <dsterba@suse.com>
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 Restructured Text 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.