From 81243eacfa400f5f7b89f4c2323d0de9982bb0fb Mon Sep 17 00:00:00 2001 From: Alexey Dobriyan Date: Fri, 7 Oct 2016 17:03:12 -0700 Subject: cred: simpler, 1D supplementary groups Current supplementary groups code can massively overallocate memory and is implemented in a way so that access to individual gid is done via 2D array. If number of gids is <= 32, memory allocation is more or less tolerable (140/148 bytes). But if it is not, code allocates full page (!) regardless and, what's even more fun, doesn't reuse small 32-entry array. 2D array means dependent shifts, loads and LEAs without possibility to optimize them (gid is never known at compile time). All of the above is unnecessary. Switch to the usual trailing-zero-len-array scheme. Memory is allocated with kmalloc/vmalloc() and only as much as needed. Accesses become simpler (LEA 8(gi,idx,4) or even without displacement). Maximum number of gids is 65536 which translates to 256KB+8 bytes. I think kernel can handle such allocation. On my usual desktop system with whole 9 (nine) aux groups, struct group_info shrinks from 148 bytes to 44 bytes, yay! Nice side effects: - "gi->gid[i]" is shorter than "GROUP_AT(gi, i)", less typing, - fix little mess in net/ipv4/ping.c should have been using GROUP_AT macro but this point becomes moot, - aux group allocation is persistent and should be accounted as such. Link: http://lkml.kernel.org/r/20160817201927.GA2096@p183.telecom.by Signed-off-by: Alexey Dobriyan Cc: Vasily Kulikov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- net/ipv4/ping.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) (limited to 'net/ipv4/ping.c') diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c index 66ddcb60519a..7cf7d6e380c2 100644 --- a/net/ipv4/ping.c +++ b/net/ipv4/ping.c @@ -258,7 +258,7 @@ int ping_init_sock(struct sock *sk) struct net *net = sock_net(sk); kgid_t group = current_egid(); struct group_info *group_info; - int i, j, count; + int i; kgid_t low, high; int ret = 0; @@ -270,16 +270,11 @@ int ping_init_sock(struct sock *sk) return 0; group_info = get_current_groups(); - count = group_info->ngroups; - for (i = 0; i < group_info->nblocks; i++) { - int cp_count = min_t(int, NGROUPS_PER_BLOCK, count); - for (j = 0; j < cp_count; j++) { - kgid_t gid = group_info->blocks[i][j]; - if (gid_lte(low, gid) && gid_lte(gid, high)) - goto out_release_group; - } + for (i = 0; i < group_info->ngroups; i++) { + kgid_t gid = group_info->gid[i]; - count -= cp_count; + if (gid_lte(low, gid) && gid_lte(gid, high)) + goto out_release_group; } ret = -EACCES; -- cgit v1.2.3