Re: [RFC v7 13/41] richacl: Check if an acl is equivalent to a file mode
From: Austin S Hemmelgarn <hidden>
Date: 2015-09-21 17:00:40
On 2015-09-21 10:38, J. Bruce Fields wrote:
On Mon, Sep 21, 2015 at 09:59:07AM -0400, Austin S Hemmelgarn wrote:quoted
On 2015-09-17 20:56, J. Bruce Fields wrote:quoted
On Thu, Sep 17, 2015 at 02:22:19PM -0400, bfields wrote:quoted
On Sat, Sep 05, 2015 at 12:27:08PM +0200, Andreas Gruenbacher wrote:quoted
ACLs are considered equivalent to file modes if they only consist of owner@, group@, and everyone@ entries, the owner@ permissions do not depend on whether the owner is a member in the owning group, and no inheritance flags are set. This test is used to avoid storing richacls if the acl can be computed from the file permission bits.We're assuming here that it's OK for us to silently rearrange an ACL as long as the result is still equivalent (in the sense that the permission algorithm would always produce the same result). I guess that's OK by me, but it might violate user expectations in some simple common cases, so may be worth mentioning in documentation someplace if we don't already.Also your notion of mode-equivalence here is interesting, it's actually a strict subset of the ACLs that produce the same permission results as a mode. (For example, everyone:rwx,bfields:rwx is equivalent to 0777 but won't be considered mode-equivalent by this algorithm.)Although it could also be equivalent to 0707, or (if bfields is the group name also) 0077, or even (if bfields isn't the group or owner of the file) 0007.I disagree. I think you've misread my example ACL (may be my sloppy notation, sorry) or misunderstood the ACL evalutation algorithm.
I'm just saying in general that there isn't enough information without knowing not only the ACL, but also the ownership information, to determine exact mode-equivalence. I didn't phrase it well to convey this though. I can kind of understand the more I think about it why an ACL only covering the owner and everyone permissions would not be considered equivalent to 0777 (strictly speaking it's 0707, even though (I think) this behaves like 0777).
quoted
Mode equivalence get's even trickier when you throw in permissions just beyond rwx (for example, by Windows standards, the usage of the execute bit on directories is weird (they have a separate permission in their ACE's for directory listing), or by VMS standards, write permission on a directory doesn't mean that you can delete things in it (VMS actually had a separate bit for the delete permission, and even had separate permissions for system access)).I believe these patches handle all of those details correctly; if you see anything to the contrary, please do speak up.
I see absolutely nothing wrong with them, I was just trying to point out that when you consider all the permissions allowed under the proposed system, mode-equivalence get's really tricky.
Note that Windows also has a DELETE bit, though it is ORed with the directory permission not ANDed (so it is sufficient for the directory to allow MAY_DELETE_CHILD *or* for the file to allow DELETE).
Yeah, which has ironically caused issues for a number of people I know before. There's all kinds of weird things you can do with Windows ACE's, for example, I'm pretty sure it's possible to let someone read just the file contents, but nothing else about it, or make it so that someone can modify the timestamps on it but not do anything else to it.
(But I believe you're correct that VMS required both permissions, if e.g. http://www.djesys.com/vms/freevms/mentor/vms_prot.html is correct). --b.quoted
quoted
I think the choices you've made probably make the most sense, they just wouldn't have been obvious to me. Anyway, so, OK by me: Reviewed-by: J. Bruce Fields [off-list ref] --b.quoted
--b.quoted
Signed-off-by: Andreas Gruenbacher <redacted> --- fs/richacl_base.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/richacl.h | 1 + 2 files changed, 105 insertions(+)diff --git a/fs/richacl_base.c b/fs/richacl_base.c index 3163152..106e988 100644 --- a/fs/richacl_base.c +++ b/fs/richacl_base.c@@ -379,3 +379,107 @@ richacl_chmod(struct richacl *acl, mode_t mode) return clone; } EXPORT_SYMBOL_GPL(richacl_chmod); + +/** + * richacl_equiv_mode - compute the mode equivalent of @acl + * + * An acl is considered equivalent to a file mode if it only consists of + * owner@, group@, and everyone@ entries and the owner@ permissions do not + * depend on whether the owner is a member in the owning group. + */ +int +richacl_equiv_mode(const struct richacl *acl, mode_t *mode_p) +{ + mode_t mode = *mode_p; + + /* + * The RICHACE_DELETE_CHILD flag is meaningless for non-directories, so + * we ignore it. + */ + unsigned int x = S_ISDIR(mode) ? 0 : RICHACE_DELETE_CHILD; + struct { + unsigned int allowed; + unsigned int defined; /* allowed or denied */ + } owner = { + .defined = RICHACE_POSIX_ALWAYS_ALLOWED | + RICHACE_POSIX_OWNER_ALLOWED | x, + }, group = { + .defined = RICHACE_POSIX_ALWAYS_ALLOWED | x, + }, everyone = { + .defined = RICHACE_POSIX_ALWAYS_ALLOWED | x, + }; + const struct richace *ace; + + if (acl->a_flags & ~(RICHACL_WRITE_THROUGH | RICHACL_MASKED)) + return -1; + + richacl_for_each_entry(ace, acl) { + if (ace->e_flags & ~RICHACE_SPECIAL_WHO) + return -1; + + if (richace_is_owner(ace) || richace_is_everyone(ace)) { + x = ace->e_mask & ~owner.defined; + if (richace_is_allow(ace)) { + unsigned int group_denied = + group.defined & ~group.allowed; + + if (x & group_denied) + return -1; + owner.allowed |= x; + } else /* if (richace_is_deny(ace)) */ { + if (x & group.allowed) + return -1; + } + owner.defined |= x; + + if (richace_is_everyone(ace)) { + x = ace->e_mask; + if (richace_is_allow(ace)) { + group.allowed |= + x & ~group.defined; + everyone.allowed |= + x & ~everyone.defined; + } + group.defined |= x; + everyone.defined |= x; + } + } else if (richace_is_group(ace)) { + x = ace->e_mask & ~group.defined; + if (richace_is_allow(ace)) + group.allowed |= x; + group.defined |= x; + } else + return -1; + } + + if (group.allowed & ~owner.defined) + return -1; + + if (acl->a_flags & RICHACL_MASKED) { + if (acl->a_flags & RICHACL_WRITE_THROUGH) { + owner.allowed = acl->a_owner_mask; + everyone.allowed = acl->a_other_mask; + } else { + owner.allowed &= acl->a_owner_mask; + everyone.allowed &= acl->a_other_mask; + } + group.allowed &= acl->a_group_mask; + } + + mode = (mode & ~S_IRWXUGO) | + (richacl_mask_to_mode(owner.allowed) << 6) | + (richacl_mask_to_mode(group.allowed) << 3) | + richacl_mask_to_mode(everyone.allowed); + + /* Mask flags we can ignore */ + x = S_ISDIR(mode) ? 0 : RICHACE_DELETE_CHILD; + + if (((richacl_mode_to_mask(mode >> 6) ^ owner.allowed) & ~x) || + ((richacl_mode_to_mask(mode >> 3) ^ group.allowed) & ~x) || + ((richacl_mode_to_mask(mode) ^ everyone.allowed) & ~x)) + return -1; + + *mode_p = mode; + return 0; +} +EXPORT_SYMBOL_GPL(richacl_equiv_mode);diff --git a/include/linux/richacl.h b/include/linux/richacl.h index d4a576c..6535ce5 100644 --- a/include/linux/richacl.h +++ b/include/linux/richacl.h@@ -304,6 +304,7 @@ extern unsigned int richacl_mode_to_mask(mode_t); extern unsigned int richacl_want_to_mask(unsigned int); extern void richacl_compute_max_masks(struct richacl *); extern struct richacl *richacl_chmod(struct richacl *, mode_t); +extern int richacl_equiv_mode(const struct richacl *, mode_t *); /* richacl_inode.c */ extern int richacl_permission(struct inode *, const struct richacl *, int); --2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/