| Message ID | 20201117040315.28548-2-drosen@google.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2,1/3] libfs: Add generic function for setting dentry_ops | expand |
On Tue, Nov 17, 2020 at 04:03:13AM +0000, Daniel Rosenberg wrote: > This adds a function to set dentry operations at lookup time that will > work for both encrypted filenames and casefolded filenames. > > A filesystem that supports both features simultaneously can use this > function during lookup preparations to set up its dentry operations once > fscrypt no longer does that itself. > > Currently the casefolding dentry operation are always set if the > filesystem defines an encoding because the features is toggleable on > empty directories. Since we don't know what set of functions we'll > eventually need, and cannot change them later, we add just add them. > > Signed-off-by: Daniel Rosenberg <drosen@google.com> Reviewed-by: Theodore Ts'o <tytso@mit.edu> - Ted
On Tue, Nov 17, 2020 at 04:03:13AM +0000, Daniel Rosenberg wrote: > > Currently the casefolding dentry operation are always set if the > filesystem defines an encoding because the features is toggleable on > empty directories. Since we don't know what set of functions we'll > eventually need, and cannot change them later, we add just add them. This isn't a very useful explanation, since encryption can be toggled on empty directories too (at least from off to on --- not the other way). Why is casefolding different? > +static const struct dentry_operations generic_ci_dentry_ops = { > + .d_hash = generic_ci_d_hash, > + .d_compare = generic_ci_d_compare, > +}; > #endif > + > +#ifdef CONFIG_FS_ENCRYPTION > +static const struct dentry_operations generic_encrypted_dentry_ops = { > + .d_revalidate = fscrypt_d_revalidate, > +}; > +#endif > + > +#if IS_ENABLED(CONFIG_UNICODE) && IS_ENABLED(CONFIG_FS_ENCRYPTION) > +static const struct dentry_operations generic_encrypted_ci_dentry_ops = { > + .d_hash = generic_ci_d_hash, > + .d_compare = generic_ci_d_compare, > + .d_revalidate = fscrypt_d_revalidate, > +}; > +#endif > + > +/** > + * generic_set_encrypted_ci_d_ops - helper for setting d_ops for given dentry > + * @dentry: dentry to set ops on > + * > + * This function sets the dentry ops for the given dentry to handle both > + * casefolded and encrypted dentry names. > + * > + * Encryption requires d_revalidate to remove nokey names once the key is present. > + * Casefolding is toggleable on an empty directory. Since we can't change the > + * operations later on, we just add the casefolding ops if the filesystem defines an > + * encoding. > + */ There are some overly long lines here (> 80 columns). But more importantly this still isn't a good explanation. Encryption can also be enabled on empty directories; what makes casefolding different? It's also not obvious why so many different copies of the dentry operations needed, instead of just using generic_encrypted_ci_dentry_ops on all. If I'm still struggling to understand this after following these patches for a long time, I expect everyone else will have trouble too... Here's a suggestion which I think explains it a lot better. It's still possible I'm misunderstanding something, though, so please check it carefully: /** * generic_set_encrypted_ci_d_ops - helper for setting d_ops for given dentry * @dentry: dentry to set ops on * * Casefolded directories need d_hash and d_compare set, so that the dentries * contained in them are handled case-insensitively. Note that these operations * are needed on the parent directory rather than on the dentries in it, and the * casefolding flag can be enabled on an empty directory later but the * dentry_operations can't be changed later. As a result, if the filesystem has * casefolding support enabled at all, we have to give all dentries the * casefolding operations even if their inode doesn't have the casefolding flag * currently (and thus the casefolding ops would be no-ops for now). * * Encryption works differently in that the only dentry operation it needs is * d_revalidate, which it only needs on dentries that have the no-key name flag. * The no-key flag can't be set "later", so we don't have to worry about that. * * Finally, to maximize compatibility with overlayfs (which isn't compatible * with certain dentry operations) and to avoid taking an unnecessary * performance hit, we use custom dentry_operations for each possible * combination rather always installing all operations. */ > +void generic_set_encrypted_ci_d_ops(struct dentry *dentry) > +{ > +#ifdef CONFIG_FS_ENCRYPTION > + bool needs_encrypt_ops = dentry->d_flags & DCACHE_NOKEY_NAME; > +#endif > +#ifdef CONFIG_UNICODE > + bool needs_ci_ops = dentry->d_sb->s_encoding; > +#endif > +#if defined(CONFIG_FS_ENCRYPTION) && defined(CONFIG_UNICODE) > + if (needs_encrypt_ops && needs_ci_ops) { > + d_set_d_op(dentry, &generic_encrypted_ci_dentry_ops); > + return; > + } The return statement above has the wrong indentation level. > +#endif > +#ifdef CONFIG_FS_ENCRYPTION > + if (needs_encrypt_ops) { > + d_set_d_op(dentry, &generic_encrypted_dentry_ops); > + return; > + } > +#endif > +#ifdef CONFIG_UNICODE > + if (needs_ci_ops) { > + d_set_d_op(dentry, &generic_ci_dentry_ops); > + return; > + } > +#endif > +} > +EXPORT_SYMBOL(generic_set_encrypted_ci_d_ops); > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 8667d0cdc71e..11345e66353b 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -3202,6 +3202,7 @@ extern int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str); > extern int generic_ci_d_compare(const struct dentry *dentry, unsigned int len, > const char *str, const struct qstr *name); > #endif > +extern void generic_set_encrypted_ci_d_ops(struct dentry *dentry); > > #ifdef CONFIG_MIGRATION > extern int buffer_migrate_page(struct address_space *,
On Tue, Nov 17, 2020 at 10:16:49AM -0800, Eric Biggers wrote: > > Here's a suggestion which I think explains it a lot better. It's still possible > I'm misunderstanding something, though, so please check it carefully: > > /** > * generic_set_encrypted_ci_d_ops - helper for setting d_ops for given dentry > * @dentry: dentry to set ops on > * > * Casefolded directories need d_hash and d_compare set, so that the dentries > * contained in them are handled case-insensitively. Note that these operations > * are needed on the parent directory rather than on the dentries in it, and the > * casefolding flag can be enabled on an empty directory later but the > * dentry_operations can't be changed later. As a result, if the filesystem has > * casefolding support enabled at all, we have to give all dentries the > * casefolding operations even if their inode doesn't have the casefolding flag > * currently (and thus the casefolding ops would be no-ops for now). > * > * Encryption works differently in that the only dentry operation it needs is > * d_revalidate, which it only needs on dentries that have the no-key name flag. > * The no-key flag can't be set "later", so we don't have to worry about that. > * > * Finally, to maximize compatibility with overlayfs (which isn't compatible > * with certain dentry operations) and to avoid taking an unnecessary > * performance hit, we use custom dentry_operations for each possible > * combination rather always installing all operations. > */ Last line in my suggestion has a typo: "rather" => "rather than". - Eric
diff --git a/fs/libfs.c b/fs/libfs.c index fc34361c1489..dd8504f3ff5d 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -1449,4 +1449,64 @@ int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str) return 0; } EXPORT_SYMBOL(generic_ci_d_hash); + +static const struct dentry_operations generic_ci_dentry_ops = { + .d_hash = generic_ci_d_hash, + .d_compare = generic_ci_d_compare, +}; #endif + +#ifdef CONFIG_FS_ENCRYPTION +static const struct dentry_operations generic_encrypted_dentry_ops = { + .d_revalidate = fscrypt_d_revalidate, +}; +#endif + +#if IS_ENABLED(CONFIG_UNICODE) && IS_ENABLED(CONFIG_FS_ENCRYPTION) +static const struct dentry_operations generic_encrypted_ci_dentry_ops = { + .d_hash = generic_ci_d_hash, + .d_compare = generic_ci_d_compare, + .d_revalidate = fscrypt_d_revalidate, +}; +#endif + +/** + * generic_set_encrypted_ci_d_ops - helper for setting d_ops for given dentry + * @dentry: dentry to set ops on + * + * This function sets the dentry ops for the given dentry to handle both + * casefolded and encrypted dentry names. + * + * Encryption requires d_revalidate to remove nokey names once the key is present. + * Casefolding is toggleable on an empty directory. Since we can't change the + * operations later on, we just add the casefolding ops if the filesystem defines an + * encoding. + */ +void generic_set_encrypted_ci_d_ops(struct dentry *dentry) +{ +#ifdef CONFIG_FS_ENCRYPTION + bool needs_encrypt_ops = dentry->d_flags & DCACHE_NOKEY_NAME; +#endif +#ifdef CONFIG_UNICODE + bool needs_ci_ops = dentry->d_sb->s_encoding; +#endif +#if defined(CONFIG_FS_ENCRYPTION) && defined(CONFIG_UNICODE) + if (needs_encrypt_ops && needs_ci_ops) { + d_set_d_op(dentry, &generic_encrypted_ci_dentry_ops); + return; + } +#endif +#ifdef CONFIG_FS_ENCRYPTION + if (needs_encrypt_ops) { + d_set_d_op(dentry, &generic_encrypted_dentry_ops); + return; + } +#endif +#ifdef CONFIG_UNICODE + if (needs_ci_ops) { + d_set_d_op(dentry, &generic_ci_dentry_ops); + return; + } +#endif +} +EXPORT_SYMBOL(generic_set_encrypted_ci_d_ops); diff --git a/include/linux/fs.h b/include/linux/fs.h index 8667d0cdc71e..11345e66353b 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -3202,6 +3202,7 @@ extern int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str); extern int generic_ci_d_compare(const struct dentry *dentry, unsigned int len, const char *str, const struct qstr *name); #endif +extern void generic_set_encrypted_ci_d_ops(struct dentry *dentry); #ifdef CONFIG_MIGRATION extern int buffer_migrate_page(struct address_space *,
This adds a function to set dentry operations at lookup time that will work for both encrypted filenames and casefolded filenames. A filesystem that supports both features simultaneously can use this function during lookup preparations to set up its dentry operations once fscrypt no longer does that itself. Currently the casefolding dentry operation are always set if the filesystem defines an encoding because the features is toggleable on empty directories. Since we don't know what set of functions we'll eventually need, and cannot change them later, we add just add them. Signed-off-by: Daniel Rosenberg <drosen@google.com> --- fs/libfs.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++ include/linux/fs.h | 1 + 2 files changed, 61 insertions(+)