[PATCH v2 0/6] convert efivarfs to manage object data correctly

James Bottomley
2025-01-07T02:36:26Z

I've added fsdevel because I'm hopping some kind vfs person will check
the shift from efivarfs managing its own data to its data being
managed as part of the vfs object lifetimes. The following paragraph
should describe all you need to know about the unusual features of the
filesystem.

efivarfs is a filesystem projecting the current state of the UEFI
variable store and allowing updates via write. Because EFI variables
contain both contents and a set of attributes, which can't be mapped
to filesystem data, the u32 attribute is prepended to the output of
the file and, since UEFI variables can't be empty, this makes every
file at least 5 characters long. EFI variables can be removed either
by doing an unlink (easy) or by doing a conventional write update that
reduces the content to zero size, which means any write update can
potentially remove the file.

Currently efivarfs has two bugs: it leaks memory and if a create is
attempted that results in an error in the write, it creates a zero
length file remnant that doesn't represent an EFI variable (i.e. the
state reflection of the EFI variable store goes out of sync).

The code uses inode->i_private to point to additionaly allocated
information but tries to maintain a global list of the shadowed
varibles for internal tracking. Forgetting to kfree() entries in this
list when they are deleted is the source of the memory leak.

I've tried to make the patches as easily reviewable by non-EFI people
as possible, so some possible cleanups (like consolidating or removing
the efi lock handling and possibly removing the additional entry
allocation entirely in favour of simply converting the dentry name to
the variable name and guid) are left for later.

The first patch removes some unused fields in the entry; patches 2-3
eliminate the list search for duplication (some EFI variable stores
have buggy iterators) and replaces it with a dcache lookup. Patch 4
move responsibility for freeing the entry data to inode eviction which
both fixes the memory leak and also means we no longer need to iterate
over the variable list and free its entries in kill_sb. Since the
variable list is now unused, patch 5 removes it and its helper
functions.

Patch 6 fixes the second bug by introducing a file_operations->release
method that checks to see if the inode size is zero when the file is
closed and removes it if it is. Since all files must be at least 5 in
length we use a zero i_size as an indicator that either the variable
was removed on write or that it wasn't correctly created in the first
place.

v2: folded in feedback from Al Viro: check errors on lookup and delete
zero length file on last close

James

---

James Bottomley (6):
efivarfs: remove unused efi_varaible.Attributes and .kobj
efivarfs: add helper to convert from UC16 name and GUID to utf8 name
efivarfs: make variable_is_present use dcache lookup
efivarfs: move freeing of variable entry into evict_inode
efivarfs: remove unused efivarfs_list
efivarfs: fix error on write to new variable leaving remnants

fs/efivarfs/file.c | 60 +++++++++++---
fs/efivarfs/inode.c | 5 --
fs/efivarfs/internal.h | 19 ++---
fs/efivarfs/super.c | 68 +++++++++-------
fs/efivarfs/vars.c | 179 ++++++++++-------------------------------
5 files changed, 136 insertions(+), 195 deletions(-)

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2.35.3