Messages in this thread | | | Date | Mon, 2 Jul 2007 10:21:36 -0500 | From | "Serge E. Hallyn" <> | Subject | Re: [PATCH 1/1] file caps: update selinux xattr hooks |
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Quoting Stephen Smalley (sds@tycho.nsa.gov): > On Thu, 2007-06-28 at 13:22 -0500, Serge E. Hallyn wrote: > > This fixes a shortcoming of the cap_setfcap patch I sent earlier, > > pointed out by Stephen Smalley. > > > > Seems to compile and boot on my little systems. > > > > thanks, > > -serge > > > > >From d729000b922a2877a48ce2b5a03a9366d8c65d04 Mon Sep 17 00:00:00 2001 > > From: Serge E. Hallyn <serue@us.ibm.com> > > Date: Thu, 28 Jun 2007 11:57:19 -0400 > > Subject: [PATCH 1/1] file caps: update selinux xattr hooks > > > > SELinux does not call out to it's secondary module for setxattr > > or removexattr mediation, as the secondary module would > > incorrectly prevent writing of selinux xattrs. This means > > that when selinux and capability are both loaded, admins will > > be able to write file capabilities with CAP_SYS_ADMIN as before, > > not with CAP_SETFCAP. > > > > Update the selinux hooks to hardcode logic for the special > > consideration for file caps. > > > > I changed the flow of the removexattr hook to reduce the amount > > of indentation I was getting. It was probably written the way > > it was for a reason, and if it was, I apologize and will > > rewrite :) If it wasn't, hopefully this way is ok. > > > > Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> > > --- > > security/selinux/hooks.c | 75 +++++++++++++++++++++++++++++---------------- > > 1 files changed, 48 insertions(+), 27 deletions(-) > > > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > > index af42820..db0a4ed 100644 > > --- a/security/selinux/hooks.c > > +++ b/security/selinux/hooks.c > > @@ -2289,6 +2289,30 @@ static int selinux_inode_getattr(struct vfsmount *mnt, struct dentry *dentry) > > return dentry_has_perm(current, mnt, dentry, FILE__GETATTR); > > } > > > > +/* called by selinux_inode_setxattr to mediate setting > > + * of non-selinux xattrs */ > > +static int selinux_inode_setotherxattr(struct dentry *dentry, char *name) > > +{ > > + if (strncmp(name, XATTR_SECURITY_PREFIX, > > + sizeof XATTR_SECURITY_PREFIX - 1)) > > + return dentry_has_perm(current, NULL, dentry, FILE__SETATTR); > > + > > + /* a file capability requires cap_setfcap */ > > + if (!strcmp(name, XATTR_NAME_CAPS)) { > > + if (!capable(CAP_SETFCAP)) > > + return -EPERM; > > + else > > + return 0; > > + } > > + > > + /* A different attribute in the security namespace. > > + Restrict to administrator. */ > > + if (!capable(CAP_SYS_ADMIN)) > > + return -EPERM; > > + > > + return 0; > > +} > > In reworking the flow of this code, you've changed the behavior (more so > than you intended) - your checking above only applies the FILE__SETATTR > check if dealing with a non-security attribute, whereas the original
Crud. I *thought* I had a clue what I was doing.
Will give it another try.
thanks, -serge
> logic (below) applied that check to all non-selinux attributes. So with > your new logic, we don't get any process-to-object check for > security.cap or security.<other>, and thus lose the domain-to-type check > or the level-to-level check. > > > @@ -2299,19 +2323,8 @@ static int selinux_inode_setxattr(struct dentry *dentry, char *name, void *value > > u32 newsid; > > int rc = 0; > > > > - if (strcmp(name, XATTR_NAME_SELINUX)) { > > - if (!strncmp(name, XATTR_SECURITY_PREFIX, > > - sizeof XATTR_SECURITY_PREFIX - 1) && > > - !capable(CAP_SYS_ADMIN)) { > > - /* A different attribute in the security namespace. > > - Restrict to administrator. */ > > - return -EPERM; > > - } > > Note that if setting a security.<non-selinux> attribute, we first check > the capability but then fall through on success to the FILE__SETATTR > check below. > > > - > > - /* Not an attribute we recognize, so just check the > > - ordinary setattr permission. */ > > - return dentry_has_perm(current, NULL, dentry, FILE__SETATTR); > > - } > > + if (strcmp(name, XATTR_NAME_SELINUX)) > > + return selinux_inode_setotherxattr(dentry, name); > > > > sbsec = inode->i_sb->s_security; > > if (sbsec->behavior == SECURITY_FS_USE_MNTPOINT) > > @@ -2385,24 +2398,32 @@ static int selinux_inode_listxattr (struct dentry *dentry) > > > > static int selinux_inode_removexattr (struct dentry *dentry, char *name) > > { > > - if (strcmp(name, XATTR_NAME_SELINUX)) { > > - if (!strncmp(name, XATTR_SECURITY_PREFIX, > > - sizeof XATTR_SECURITY_PREFIX - 1) && > > - !capable(CAP_SYS_ADMIN)) { > > - /* A different attribute in the security namespace. > > - Restrict to administrator. */ > > - return -EPERM; > > - } > > + /* No one is allowed to remove a SELinux security label. > > + You can change the label, but all data must be labeled. */ > > + if (!strcmp(name, XATTR_NAME_SELINUX)) > > + return -EACCES; > > > > - /* Not an attribute we recognize, so just check the > > - ordinary setattr permission. Might want a separate > > - permission for removexattr. */ > > + /* Not an attribute we recognize, so just check the > > + ordinary setattr permission. Might want a separate > > + permission for removexattr. */ > > + if (strncmp(name, XATTR_SECURITY_PREFIX, > > + sizeof XATTR_SECURITY_PREFIX - 1)) > > return dentry_has_perm(current, NULL, dentry, FILE__SETATTR); > > Same problem here - when you changed the flow, you unintentionally > changed the behavior. > > > + > > + /* a file capability requires cap_setfcap */ > > + if (!strcmp(name, XATTR_NAME_CAPS)) { > > + if (!capable(CAP_SETFCAP)) > > + return -EPERM; > > + else > > + return 0; > > } > > > > - /* No one is allowed to remove a SELinux security label. > > - You can change the label, but all data must be labeled. */ > > - return -EACCES; > > + /* A different attribute in the security namespace. > > + Restrict to administrator. */ > > + if (!capable(CAP_SYS_ADMIN)) > > + return -EPERM; > > + > > + return 0; > > } > > > > static const char *selinux_inode_xattr_getsuffix(void) > -- > Stephen Smalley > National Security Agency > > - > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > the body of a message to majordomo@vger.kernel.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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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