Messages in this thread Patch in this message | | | Date | Thu, 24 Jan 2013 16:46:12 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH v2] userns: improve uid/gid map collision detection |
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On Thu, 24 Jan 2013 10:28:59 -0500 Aristeu Rozanski <aris@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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