From a293980c2e261bd5b0d2a77340dd04f684caff58 Mon Sep 17 00:00:00 2001 From: Neil Horman Date: Wed, 23 Sep 2009 15:56:56 -0700 Subject: [PATCH] exec: let do_coredump() limit the number of concurrent dumps to pipes Introduce core pipe limiting sysctl. Since we can dump cores to pipe, rather than directly to the filesystem, we create a condition in which a user can create a very high load on the system simply by running bad applications. If the pipe reader specified in core_pattern is poorly written, we can have lots of ourstandig resources and processes in the system. This sysctl introduces an ability to limit that resource consumption. core_pipe_limit defines how many in-flight dumps may be run in parallel, dumps beyond this value are skipped and a note is made in the kernel log. A special value of 0 in core_pipe_limit denotes unlimited core dumps may be handled (this is the default value). [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Neil Horman Reported-by: Earl Chew Cc: Oleg Nesterov Cc: Andi Kleen Cc: Alan Cox Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/sysctl/kernel.txt | 22 ++++++++++++++++++++++ fs/exec.c | 23 ++++++++++++++++++----- kernel/sysctl.c | 9 +++++++++ 3 files changed, 49 insertions(+), 5 deletions(-) diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index b3d8b4922740..a028b92001ed 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -22,6 +22,7 @@ show up in /proc/sys/kernel: - callhome [ S390 only ] - auto_msgmni - core_pattern +- core_pipe_limit - core_uses_pid - ctrl-alt-del - dentry-state @@ -135,6 +136,27 @@ core_pattern is used to specify a core dumpfile pattern name. ============================================================== +core_pipe_limit: + +This sysctl is only applicable when core_pattern is configured to pipe core +files to user space helper a (when the first character of core_pattern is a '|', +see above). When collecting cores via a pipe to an application, it is +occasionally usefull for the collecting application to gather data about the +crashing process from its /proc/pid directory. In order to do this safely, the +kernel must wait for the collecting process to exit, so as not to remove the +crashing processes proc files prematurely. This in turn creates the possibility +that a misbehaving userspace collecting process can block the reaping of a +crashed process simply by never exiting. This sysctl defends against that. It +defines how many concurrent crashing processes may be piped to user space +applications in parallel. If this value is exceeded, then those crashing +processes above that value are noted via the kernel log and their cores are +skipped. 0 is a special value, indicating that unlimited processes may be +captured in parallel, but that no waiting will take place (i.e. the collecting +process is not guaranteed access to /proc//). This value defaults +to 0. + +============================================================== + core_uses_pid: The default coredump filename is "core". By setting diff --git a/fs/exec.c b/fs/exec.c index 735d9c18ec71..dc022dd15d51 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -63,6 +63,7 @@ int core_uses_pid; char core_pattern[CORENAME_MAX_SIZE] = "core"; +unsigned int core_pipe_limit; int suid_dumpable = 0; /* The maximal length of core_pattern is also specified in sysctl.c */ @@ -1744,7 +1745,8 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs) unsigned long core_limit = current->signal->rlim[RLIMIT_CORE].rlim_cur; char **helper_argv = NULL; int helper_argc = 0; - char *delimit; + int dump_count = 0; + static atomic_t core_dump_count = ATOMIC_INIT(0); audit_core_dumps(signr); @@ -1826,28 +1828,36 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs) goto fail_unlock; } + dump_count = atomic_inc_return(&core_dump_count); + if (core_pipe_limit && (core_pipe_limit < dump_count)) { + printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n", + task_tgid_vnr(current), current->comm); + printk(KERN_WARNING "Skipping core dump\n"); + goto fail_dropcount; + } + helper_argv = argv_split(GFP_KERNEL, corename+1, &helper_argc); if (!helper_argv) { printk(KERN_WARNING "%s failed to allocate memory\n", __func__); - goto fail_unlock; + goto fail_dropcount; } core_limit = RLIM_INFINITY; /* SIGPIPE can happen, but it's just never processed */ - if (call_usermodehelper_pipe(corename+1, helper_argv, NULL, + if (call_usermodehelper_pipe(helper_argv[0], helper_argv, NULL, &file)) { printk(KERN_INFO "Core dump to %s pipe failed\n", corename); - goto fail_unlock; + goto fail_dropcount; } } else file = filp_open(corename, O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag, 0600); if (IS_ERR(file)) - goto fail_unlock; + goto fail_dropcount; inode = file->f_path.dentry->d_inode; if (inode->i_nlink > 1) goto close_fail; /* multiple links - don't dump */ @@ -1877,6 +1887,9 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs) current->signal->group_exit_code |= 0x80; close_fail: filp_close(file, NULL); +fail_dropcount: + if (dump_count) + atomic_dec(&core_dump_count); fail_unlock: if (helper_argv) argv_free(helper_argv); diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 7f4f57bea4ce..37abb8c3995b 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -76,6 +76,7 @@ extern int max_threads; extern int core_uses_pid; extern int suid_dumpable; extern char core_pattern[]; +extern unsigned int core_pipe_limit; extern int pid_max; extern int min_free_kbytes; extern int pid_max_min, pid_max_max; @@ -423,6 +424,14 @@ static struct ctl_table kern_table[] = { .proc_handler = &proc_dostring, .strategy = &sysctl_string, }, + { + .ctl_name = CTL_UNNUMBERED, + .procname = "core_pipe_limit", + .data = &core_pipe_limit, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = &proc_dointvec, + }, #ifdef CONFIG_PROC_SYSCTL { .procname = "tainted",