Re: [PATCH] NFS: Remove superfluous kmap in nfs_readdir_xdr_to_array

[Sasha Levin <sashal@kernel.org>]

On Fri, Mar 13, 2020 at 02:05:27PM -0700, Linus Torvalds wrote:
>Adding more people.
>
>The old stable trees seem to have rather different code.
>
>[ Goes off and looks at the stable trees ]
>
>Petr seems entirely correct - the stable tree backport appears broken.
>
>Because looking at that commit 67a56e9743171 in the stable tree, it
>doesn't seem to match commit 4b310319c6a8 ("NFS: Fix memory leaks and
>corruption in readdir") in mainline.
>
>That stable backport looks bogus. It added that
>
>        array = kmap(page);
>
>line from somewhere else, probably because the stable tree didn't have
>the line at all, and it was there in the context.

I botched up that backport, sorry.

>Because while mainline has that line to initialize array with kmap(),
>in those stable trees, we have
>
>        array = nfs_readdir_get_array(page);
>
>and as Petr says, the kmap has been done there already, and it will be
>kunmap'ed by nfs_readdir_release_array().
>
>And looking closer, this same bug seems to have happened twice: it
>also exists in 0b0223f9c3a8.
>
>But somebody else should double-check me - somebody who actually knows the code.
>
>As to how I found the other case, do this in the stable git repo with
>all the stable tags:
>
>    git log -p --no-merges --all \
>        --grep="NFS: Fix memory leaks and corruption in readdir"
>
>to see all the copies of that commit backport.
>
>Add a
>
>    -S'kmap(page)'
>
>to that line to see the cases that added that line. Or to just get the commits:
>
>    git log --oneline --no-merges --all \
>        --grep="NFS: Fix memory leaks and corruption in readdir" \
>        -S'kmap(page)'
>
>and the result is
>
>    67a56e974317 NFS: Fix memory leaks and corruption in readdir
>    0b0223f9c3a8 NFS: Fix memory leaks and corruption in readdir

I've applied to fix to the 4.9 and 4.4 trees, thank you!

-- 
Thanks,
Sasha