On Thu, 24 Jan 2013 10:28:59 -0500
Aristeu Rozanski <a...@redhat.com> wrote:
> userns: improve uid/gid map collision detection
>
> Initial implementation of the uid/gid maps (/proc/<pid>/{u,g}id_map) will
> enforce that the UID and GID maps be written in strict order as a simple
> way to check for range collision:
> local id mapped to count/range
> 0 1000 50
> (ids 0-50 get mapped to 1000-1050)
> 100 2120 10
> 500 5000 200
> so for each new entry, local id must be bigger than last local id (plus
> count) and the ids it maps to also needs to be bigger than the last
> entry (plus count).
>
> This makes impossible to have a use case like this:
> local id mapped to count/range
> 0 1000 1
> 48 500 20
>
> because while 48+20 > 0+1, 500+20 < 1000+1.
>
> This patch implements a more elaborate collision detection allowing any
> order to be used.
>
> v2: improved the patch description as requested by Andrew
Thanks.
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -521,6 +521,28 @@ struct seq_operations proc_projid_seq_operations = {
>
> static DEFINE_MUTEX(id_map_mutex);
>
> +#define in_range(b,first,len) ((b)>=(first)&&(b)<(first)+(len))
eek, a macro! Macros are always bad.
This one is bad because
a) it's a macro
b) it evaluates its args multiple times and hence will cause nasty
bugs if called with expressions-with-side-effects.
c) it evaluates its args multiple times and if called with
non-trivial expressions the compiler might not be able to CSE those
expressions, leading to code bloat.
Add lo, this patch:
--- a/kernel/user_namespace.c~userns-improve-uid-gid-map-collision-detection-fix
+++ a/kernel/user_namespace.c
@@ -521,7 +521,11 @@ struct seq_operations proc_projid_seq_op
static DEFINE_MUTEX(id_map_mutex);
-#define in_range(b,first,len) ((b)>=(first)&&(b)<(first)+(len))
+static bool in_range(u32 b, u32 first, u32 len)
+{
+ return b >= first && b < first + len;
+}
+
static inline int extent_collision(struct uid_gid_map *new_map,
struct uid_gid_extent *extent)
{
reduces the user_namespace.o text from 4822 bytes to 4727 with
gcc-4.4.4. This is a remarkably large difference.
btw, what the heck is up with CONFIG_UIDGID_CONVERTED? That thing
prevents userns from being compiled in an allmodconfig build, which is
rather undesirable. Isn't there a better, more user-friendly way of
doing this?
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