do_umount(): add missing barrier before refcount checks in sync case

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do_umount() analogue of the race fixed in 119e1ef80e "fix
__legitimize_mnt()/mntput() race".  Here we want to make sure that
if __legitimize_mnt() doesn't notice our lock_mount_hash(), we will
notice their refcount increment.  Harder to hit than mntput_no_expire()
one, fortunately, and consequences are milder (sync umount acting
like umount -l on a rare race with RCU pathwalk hitting at just the
wrong time instead of use-after-free galore mntput_no_expire()
counterpart used to be hit).  Still a bug...

Fixes: 48a066e72d ("RCU'd vfsmounts")
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

...

This commit is contained in:

Al Viro 2025-04-28 23:56:14 -04:00

parent 250cf36930

commit 65781e19dc

1 changed files with 2 additions and 1 deletions

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fs/namespace.c

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