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cred: add cred_fscmp() for comparing creds.

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NFS needs to compare to credentials, to see if they can
be treated the same w.r.t. filesystem access.  Sometimes
an ordering is needed when credentials are used as a key
to an rbtree.
NFS currently has its own private credential management from
before 'struct cred' existed.  To move it over to more consistent
use of 'struct cred' we need a comparison function.
This patch adds that function.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
This commit is contained in:
NeilBrown 2018-12-03 11:30:30 +11:00 committed by Anna Schumaker
parent 8e2e5b7c49
commit d89b22d46a
2 changed files with 56 additions and 0 deletions
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1
include/linux/cred.h
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@ -169,6 +169,7 @@ extern int change_create_files_as(struct cred *, struct inode *);
extern int set_security_override(struct cred *, u32);
extern int set_security_override_from_ctx(struct cred *, const char *);
extern int set_create_files_as(struct cred *, struct inode *);
extern int cred_fscmp(const struct cred *, const struct cred *);
extern void __init cred_init(void);
/*

55
kernel/cred.c
View File

@ -19,6 +19,7 @@
#include <linux/security.h>
#include <linux/binfmts.h>
#include <linux/cn_proc.h>
#include <linux/uidgid.h>
#if 0
#define kdebug(FMT, ...) \
@ -564,6 +565,60 @@ void revert_creds(const struct cred *old)
}
EXPORT_SYMBOL(revert_creds);
/**
* cred_fscmp - Compare two credentials with respect to filesystem access.
* @a: The first credential
* @b: The second credential
*
* cred_cmp() will return zero if both credentials have the same
* fsuid, fsgid, and supplementary groups. That is, if they will both
* provide the same access to files based on mode/uid/gid.
* If the credentials are different, then either -1 or 1 will
* be returned depending on whether @a comes before or after @b
* respectively in an arbitrary, but stable, ordering of credentials.
*
* Return: -1, 0, or 1 depending on comparison
*/
int cred_fscmp(const struct cred *a, const struct cred *b)
{
struct group_info *ga, *gb;
int g;
if (a == b)
return 0;
if (uid_lt(a->fsuid, b->fsuid))
return -1;
if (uid_gt(a->fsuid, b->fsuid))
return 1;
if (gid_lt(a->fsgid, b->fsgid))
return -1;
if (gid_gt(a->fsgid, b->fsgid))
return 1;
ga = a->group_info;
gb = b->group_info;
if (ga == gb)
return 0;
if (ga == NULL)
return -1;
if (gb == NULL)
return 1;
if (ga->ngroups < gb->ngroups)
return -1;
if (ga->ngroups > gb->ngroups)
return 1;
for (g = 0; g < ga->ngroups; g++) {
if (gid_lt(ga->gid[g], gb->gid[g]))
return -1;
if (gid_gt(ga->gid[g], gb->gid[g]))
return 1;
}
return 0;
}
EXPORT_SYMBOL(cred_fscmp);
/*
* initialise the credentials stuff
*/