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cifs_extend_writeback can pick up a folio on an extending write which has been dirtied, but we have aclamp on the writeback to an i_size local variable, which can cause short writes, yet mark the page as clean. This can cause a data corruption. As an example, consider this scenario: 1. First write to the file happens offset 0 len 5k. 2. Writeback starts for the range (0-5k). 3. Writeback locks page 1 in cifs_writepages_begin. But does not lock page 2 yet. 4. Page 2 is now written to by the next write, which extends the file by another 5k. Page 2 and 3 are now marked dirty. 5. Now we reach cifs_extend_writeback, where we extend to include the next folio (even if it should be partially written). We will mark page 2 for writeback. 6. But after exiting cifs_extend_writeback, we will clamp the writeback to i_size, which was 5k when it started. So we write only 1k bytes in page 2. 7. We still will now mark page 2 as flushed and mark it clean. So remaining contents of page 2 will not be written to the server (hence the hole in that gap, unless that range gets overwritten). With this patch, we will make sure not extend the writeback anymore when a change in the file size is detected. This fix also changes the error handling of cifs_extend_writeback when a folio get fails. We will now stop the extension when a folio get fails. Cc: stable@kernel.org # v6.3~v6.9 Signed-off-by: Shyam Prasad N <sprasad@microsoft.com> Acked-by: David Howells <dhowells@redhat.com> Reported-by: Mark A Whiting <whitingm@opentext.com> Signed-off-by: Shyam Prasad N <sprasad@microsoft.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
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.