Alexey Dobriyan 8bb2ee192e proc: fix coredump vs read /proc/*/stat race ... do_task_stat() accesses IP and SP of a task without bumping reference count of a stack (which became an entity with independent lifetime at some point). Steps to reproduce: #include <stdio.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <sys/time.h> #include <sys/resource.h> #include <unistd.h> #include <sys/wait.h> int main(void) { setrlimit(RLIMIT_CORE, &(struct rlimit){}); while (1) { char buf[64]; char buf2[4096]; pid_t pid; int fd; pid = fork(); if (pid == 0) { *(volatile int *)0 = 0; } snprintf(buf, sizeof(buf), "/proc/%u/stat", pid); fd = open(buf, O_RDONLY); read(fd, buf2, sizeof(buf2)); close(fd); waitpid(pid, NULL, 0); } return 0; } BUG: unable to handle kernel paging request at 0000000000003fd8 IP: do_task_stat+0x8b4/0xaf0 PGD 800000003d73e067 P4D 800000003d73e067 PUD 3d558067 PMD 0 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 0 PID: 1417 Comm: a.out Not tainted 4.15.0-rc8-dirty #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1.fc27 04/01/2014 RIP: 0010:do_task_stat+0x8b4/0xaf0 Call Trace: proc_single_show+0x43/0x70 seq_read+0xe6/0x3b0 __vfs_read+0x1e/0x120 vfs_read+0x84/0x110 SyS_read+0x3d/0xa0 entry_SYSCALL_64_fastpath+0x13/0x6c RIP: 0033:0x7f4d7928cba0 RSP: 002b:00007ffddb245158 EFLAGS: 00000246 Code: 03 b7 a0 01 00 00 4c 8b 4c 24 70 4c 8b 44 24 78 4c 89 74 24 18 e9 91 f9 ff ff f6 45 4d 02 0f 84 fd f7 ff ff 48 8b 45 40 48 89 ef <48> 8b 80 d8 3f 00 00 48 89 44 24 20 e8 9b 97 eb ff 48 89 44 24 RIP: do_task_stat+0x8b4/0xaf0 RSP: ffffc90000607cc8 CR2: 0000000000003fd8 John Ogness said: for my tests I added an else case to verify that the race is hit and correctly mitigated. Link: http://lkml.kernel.org/r/20180116175054.GA11513@avx2 Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Reported-by: "Kohli, Gaurav" <gkohli@codeaurora.org> Tested-by: John Ogness <john.ogness@linutronix.de> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Ingo Molnar <mingo@elte.hu> Cc: Oleg Nesterov <oleg@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2018-01-19 10:09:41 -08:00
..
array.c	proc: fix coredump vs read /proc/*/stat race	2018-01-19 10:09:41 -08:00
base.c	proc: show si_ptr in /proc/<pid>/timers without hashing	2017-12-06 18:23:27 -08:00
cmdline.c
consoles.c
cpuinfo.c	x86 / CPU: Always show current CPU frequency in /proc/cpuinfo	2017-11-15 19:46:50 +01:00
devices.c
fd.c
fd.h
generic.c
inode.c	Rename superblock flags (MS_xyz -> SB_xyz)	2017-11-27 13:05:09 -08:00
internal.h	Merge branch 'work.whack-a-mole' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs	2017-11-22 20:20:02 -10:00
interrupts.c
Kconfig
kcore.c
kmsg.c
loadavg.c	pid: replace pid bitmap implementation with IDR API	2017-11-17 16:10:03 -08:00
Makefile	proc: : uninline name_to_int()	2017-11-17 16:10:00 -08:00
meminfo.c
namespaces.c
nommu.c
page.c
proc_net.c
proc_sysctl.c
proc_tty.c	TTY/Serial patches for 4.15-rc1	2017-11-13 21:05:31 -08:00
root.c	Rename superblock flags (MS_xyz -> SB_xyz)	2017-11-27 13:05:09 -08:00
self.c
softirqs.c
stat.c
task_mmu.c	libnvdimm for 4.15	2017-11-17 09:51:57 -08:00
task_nommu.c
thread_self.c
uptime.c
util.c	proc: use do-while in name_to_int()	2017-11-17 16:10:00 -08:00
version.c
vmcore.c