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In a bmapx call, bmv_count is the total size of the array, including the
zeroth element that userspace uses to supply the search key. The output
array starts at offset 1 so that we can set up the user for the next
invocation. Since we now can split an extent into multiple bmap records
due to shared/unshared status, we have to be careful that we don't
overflow the output array.
In the original patch f86f403794 ("xfs: teach get_bmapx about shared
extents and the CoW fork") I used cur_ext (the output index) to check
for overflows, albeit with an off-by-one error. Since nexleft no longer
describes the number of unfilled slots in the output, we can rip all
that out and use cur_ext for the overflow check directly.
Failure to do this causes heap corruption in bmapx callers such as
xfs_io and xfs_scrub. xfs/328 can reproduce this problem.
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.