ovl: make use of ->layers safe in rcu pathwalk

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ovl_permission() accesses ->layers[...].mnt; we can't have ->layers
freed without an RCU delay on fs shutdown.

Fortunately, kern_unmount_array() that is used to drop those mounts
does include an RCU delay, so freeing is delayed; unfortunately, the
array passed to kern_unmount_array() is formed by mangling ->layers
contents and that happens without any delays.

The ->layers[...].name string entries are used to store the strings to
display in "lowerdir=..." by ovl_show_options().  Those entries are not
accessed in RCU walk.

Move the name strings into a separate array ofs->config.lowerdirs and
reuse the ofs->config.lowerdirs array as the temporary mount array to
pass to kern_unmount_array().

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/r/20231002023711.GP3389589@ZenIV/
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

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This commit is contained in:

Amir Goldstein 2023-10-02 14:21:49 +03:00

parent c54719c92a

commit a535116d80

3 changed files with 21 additions and 24 deletions

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10

fs/overlayfs/ovl_entry.h

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17

fs/overlayfs/params.c

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18

fs/overlayfs/super.c

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