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afs: Don't cross .backup mountpoint from backup volume

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Don't cross a mountpoint that explicitly specifies a backup volume
(target is <vol>.backup) when starting from a backup volume.

It it not uncommon to mount a volume's backup directly in the volume
itself.  This can cause tools that are not paying attention to get
into a loop mounting the volume onto itself as they attempt to
traverse the tree, leading to a variety of problems.

This doesn't prevent the general case of loops in a sequence of
mountpoints, but addresses a common special case in the same way
as other afs clients.

Reported-by: Jan Henrik Sylvester <jan.henrik.sylvester@uni-hamburg.de>
Link: http://lists.infradead.org/pipermail/linux-afs/2024-May/008454.html
Reported-by: Markus Suvanto <markus.suvanto@gmail.com>
Link: http://lists.infradead.org/pipermail/linux-afs/2024-February/008074.html
Signed-off-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/768760.1716567475@warthog.procyon.org.uk
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Marc Dionne 2024-05-24 17:17:55 +01:00 committed by Christian Brauner
parent 712182b67e
commit 29be9100ac
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1 changed files with 5 additions and 0 deletions
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5
fs/afs/mntpt.c
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@ -140,6 +140,11 @@ static int afs_mntpt_set_params(struct fs_context *fc, struct dentry *mntpt)
put_page(page);
if (ret < 0)
return ret;
/* Don't cross a backup volume mountpoint from a backup volume */
if (src_as->volume && src_as->volume->type == AFSVL_BACKVOL &&
ctx->type == AFSVL_BACKVOL)
return -ENODEV;
}
return 0;