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ceph: give up on paths longer than PATH_MAX

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commit 550f7ca98e upstream.

If the full path to be built by ceph_mdsc_build_path() happens to be
longer than PATH_MAX, then this function will enter an endless (retry)
loop, effectively blocking the whole task.  Most of the machine
becomes unusable, making this a very simple and effective DoS
vulnerability.

I cannot imagine why this retry was ever implemented, but it seems
rather useless and harmful to me.  Let's remove it and fail with
ENAMETOOLONG instead.

Cc: stable@vger.kernel.org
Reported-by: Dario Weißer <dario@cure53.de>
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Reviewed-by: Alex Markuze <amarkuze@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
[idryomov@gmail.com: backport to 6.1: pr_warn() is still in use]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Max Kellermann 2024-11-18 23:28:28 +01:00 committed by Greg Kroah-Hartman
parent 14c02f4e69
commit 0f2b2d9e88
1 changed files with 4 additions and 5 deletions
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9
fs/ceph/mds_client.c
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@ -2451,12 +2451,11 @@ retry:
if (pos < 0) {
/*
* A rename didn't occur, but somehow we didn't end up where
* we thought we would. Throw a warning and try again.
* The path is longer than PATH_MAX and this function
* cannot ever succeed. Creating paths that long is
* possible with Ceph, but Linux cannot use them.
*/
pr_warn("build_path did not end path lookup where "
"expected, pos is %d\n", pos);
goto retry;
return ERR_PTR(-ENAMETOOLONG);
}
*pbase = base;