commit b7b2562f7252 ("kernel/groups.c: use sort library function")
introduced the sort library function.
also use the bsearch library function instead of open-coding the binary
search.
Signed-off-by: Thomas Meyer <[email protected]>
---
kernel/groups.c | 17 ++++-------------
1 file changed, 4 insertions(+), 13 deletions(-)
diff --git a/kernel/groups.c b/kernel/groups.c
index daae2f2dc6d4f..69561a9cb4d39 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -2,6 +2,7 @@
/*
* Supplementary group IDs
*/
+#include <linux/bsearch.h>
#include <linux/cred.h>
#include <linux/export.h>
#include <linux/slab.h>
@@ -96,22 +97,12 @@ EXPORT_SYMBOL(groups_sort);
/* a simple bsearch */
int groups_search(const struct group_info *group_info, kgid_t grp)
{
- unsigned int left, right;
-
if (!group_info)
return 0;
- left = 0;
- right = group_info->ngroups;
- while (left < right) {
- unsigned int mid = (left+right)/2;
- if (gid_gt(grp, group_info->gid[mid]))
- left = mid + 1;
- else if (gid_lt(grp, group_info->gid[mid]))
- right = mid;
- else
- return 1;
- }
+ if (bsearch(&grp, group_info->gid, group_info->ngroups,
+ sizeof(*group_info->gid), gid_cmp))
+ return 1;
return 0;
}
--
2.21.0
On 07/10/2019 21.26, Thomas Meyer wrote:
> commit b7b2562f7252 ("kernel/groups.c: use sort library function")
> introduced the sort library function.
> also use the bsearch library function instead of open-coding the binary
> search.
Yes, but please note the difference between sorting the group_info and
searching it: The former is done quite rarely - the setgroups syscall is
used roughly once per login-session.
But the searching of that structure is done more or less every time a
user accesses a file not owned by that user (e.g., any time a normal
user accesses anything in /usr) - at least if I'm reading
acl_permission_check() right.
So using a callback-based interface, especially in a post-spectre world,
may have a somewhat large performance impact.
Rasmus
Rasmus Villemoes <[email protected]> writes:
> On 07/10/2019 21.26, Thomas Meyer wrote:
>> commit b7b2562f7252 ("kernel/groups.c: use sort library function")
>> introduced the sort library function.
>> also use the bsearch library function instead of open-coding the binary
>> search.
Hi,
> Yes, but please note the difference between sorting the group_info and
> searching it: The former is done quite rarely - the setgroups syscall is
> used roughly once per login-session.
>
> But the searching of that structure is done more or less every time a
> user accesses a file not owned by that user (e.g., any time a normal
> user accesses anything in /usr) - at least if I'm reading
> acl_permission_check() right.
>
> So using a callback-based interface, especially in a post-spectre world,
> may have a somewhat large performance impact.
okay, so the code is duplicated for performance reasons? nothing a
compiler can inline, I guess.
so what about a comment instead:
diff --git a/kernel/groups.c b/kernel/groups.c
index daae2f2dc6d4f..46b5d4cd53c2e 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -93,7 +93,7 @@ void groups_sort(struct group_info *group_info)
}
EXPORT_SYMBOL(groups_sort);
-/* a simple bsearch */
+/* duplicate code from lib/bsearch.c for performance reasons */
int groups_search(const struct group_info *group_info, kgid_t grp)
{
unsigned int left, right;
Mfg
thomas