From: Neil Brown 1/ If a setuid process swaps it's real and effective uids and then forks, the fork fails if the new realuid has more processes than the original process was limited to. This is particularly a problem if a user with a process limit (e.g. 256) runs a setuid-root program which does setuid() + fork() (e.g. lprng) while root already has more than 256 process (which is quite possible). The root problem here is that a limit which should be a per-user limit is being implemented as a per-process limit with per-process (e.g. CAP_SYS_RESOURCE) controls. Being a per-user limit, it should be that the root-user can over-ride it, not just some process with CAP_SYS_RESOURCE. This patch adds a test to ignore process limits if the real user is root. 2/ When a root-owned process (e.g. cgiwrap) sets up process limits and then calls setuid, the setuid should fail if the user would then be running more than rlim_cur[RLIMIT_NPROC] processes, but it doesn't. This patch adds an appropriate test. With this patch, and per-user process limit imposed in cgiwrap really works. kernel/fork.c | 6 ++++-- kernel/sys.c | 8 ++++++++ 2 files changed, 12 insertions(+), 2 deletions(-) diff -puN kernel/fork.c~RLIMIT_NPROC-fixes kernel/fork.c --- 25/kernel/fork.c~RLIMIT_NPROC-fixes 2003-07-13 21:54:30.000000000 -0700 +++ 25-akpm/kernel/fork.c 2003-07-13 21:54:30.000000000 -0700 @@ -759,8 +759,10 @@ struct task_struct *copy_process(unsigne goto fork_out; retval = -EAGAIN; - if (atomic_read(&p->user->processes) >= p->rlim[RLIMIT_NPROC].rlim_cur) { - if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE)) + if (atomic_read(&p->user->processes) >= + p->rlim[RLIMIT_NPROC].rlim_cur) { + if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) && + p->user != &root_user) goto bad_fork_free; } diff -puN kernel/sys.c~RLIMIT_NPROC-fixes kernel/sys.c --- 25/kernel/sys.c~RLIMIT_NPROC-fixes 2003-07-13 21:54:30.000000000 -0700 +++ 25-akpm/kernel/sys.c 2003-07-13 21:54:30.000000000 -0700 @@ -601,6 +601,14 @@ static int set_user(uid_t new_ruid, int new_user = alloc_uid(new_ruid); if (!new_user) return -EAGAIN; + + if (atomic_read(&new_user->processes) >= + current->rlim[RLIMIT_NPROC].rlim_cur && + new_user != &root_user) { + free_uid(new_user); + return -EAGAIN; + } + switch_uid(new_user); if(dumpclear) _