From e14ea3f5c37475e12a3b7fb7bd3165b0a4e77c51 Mon Sep 17 00:00:00 2001 From: Csaba Henk Date: Wed, 5 Jul 2017 17:48:37 +0200 Subject: groups: don't allocate auxiliary gid list on stack When glusterfs wants to retrieve the list of auxiliary gids of a user, it typically allocates a sufficiently big gid_t array on stack and calls getgrouplist(3) with it. However, "sufficiently big" means to be of maximum supported gid list size, which in GlusterFS is GF_MAX_AUX_GROUPS = 64k. That means a 64k * sizeof(gid_t) = 256k allocation, which is big enough to overflow the stack in certain cases. A further observation is that stack allocation of the gid list brings no gain, as in all cases the content of the gid list eventually gets copied over to a heap allocated buffer. So we add a convenience wrapper of getgrouplist to libglusterfs called gf_getgrouplist which calls getgrouplist with a sufficiently big heap allocated buffer (it takes care of the allocation too). We are porting all the getgrouplist invocations to gf_getgrouplist and thus eliminate the huge stack allocation. BUG: 1464327 Change-Id: Icea76d0d74dcf2f87d26cb299acc771ca3b32d2b Signed-off-by: Csaba Henk Reviewed-on: https://review.gluster.org/17706 Smoke: Gluster Build System Reviewed-by: Niels de Vos Reviewed-by: Amar Tumballi CentOS-regression: Gluster Build System --- libglusterfs/src/common-utils.c | 73 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) (limited to 'libglusterfs/src/common-utils.c') diff --git a/libglusterfs/src/common-utils.c b/libglusterfs/src/common-utils.c index 5015d9666b6..e5e08909ac7 100644 --- a/libglusterfs/src/common-utils.c +++ b/libglusterfs/src/common-utils.c @@ -30,6 +30,7 @@ #include #include #include /* for dirname() */ +#include #if defined(GF_BSD_HOST_OS) || defined(GF_DARWIN_HOST_OS) #include @@ -4877,3 +4878,75 @@ close_fds_except (int *fdv, size_t count) #endif /* !GF_LINUX_HOST_OS */ return 0; } + +/** + * gf_getgrouplist - get list of groups to which a user belongs + * + * A convenience wrapper for getgrouplist(3). + * + * @param user - same as in getgrouplist(3) + * @param group - same as in getgrouplist(3) + * @param groups - pointer to a gid_t pointer + * + * gf_getgrouplist allocates a gid_t buffer which is big enough to + * hold the list of auxiliary group ids for user, up to the GF_MAX_AUX_GROUPS + * threshold. Upon succesfull invocation groups will be pointed to that buffer. + * + * @return success: the number of auxiliary group ids retrieved + * failure: -1 + */ +int +gf_getgrouplist (const char *user, gid_t group, gid_t **groups) +{ + int ret = -1; + int ngroups = SMALL_GROUP_COUNT; + + *groups = GF_CALLOC (sizeof (gid_t), ngroups, gf_common_mt_groups_t); + if (!*groups) + return -1; + + /* + * We are running getgrouplist() in a loop until we succeed (or hit + * certain exit conditions, see the comments below). This is because + * the indicated number of auxiliary groups that we obtain in case of + * the failure of the first invocation is not guaranteed to keep its + * validity upon the next invocation with a gid buffer of that size. + */ + for (;;) { + int ngroups_old = ngroups; + ret = getgrouplist (user, group, *groups, &ngroups); + if (ret != -1) + break; + + if (ngroups >= GF_MAX_AUX_GROUPS) { + /* + * This should not happen as GF_MAX_AUX_GROUPS is set + * to the max value of number of supported auxiliary + * groups across all platforms supported by GlusterFS. + * However, if it still happened some way, we wouldn't + * care about the incompleteness of the result, we'd + * just go on with what we got. + */ + return GF_MAX_AUX_GROUPS; + } else if (ngroups <= ngroups_old) { + /* + * There is an edge case that getgrouplist() fails but + * ngroups remains the same. This is actually not + * specified in getgrouplist(3), but implementations + * can do this upon internal failure[1]. To avoid + * falling into an infinite loop when this happens, we + * break the loop if the getgrouplist call failed + * without an increase in the indicated group number. + * + * [1] https://sourceware.org/git/?p=glibc.git;a=blob;f=grp/initgroups.c;hb=refs/heads/release/2.25/master#l168 + */ + GF_FREE (*groups); + return -1; + } + + *groups = GF_REALLOC (*groups, ngroups * sizeof (gid_t)); + if (!*groups) + return -1; + } + return ret; +} -- cgit