71 lines
2.9 KiB
Diff
71 lines
2.9 KiB
Diff
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From 957edb063f3e9751bbdc05bd973bb2190ab0e917 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
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Date: Fri, 15 Mar 2019 15:13:25 +0100
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Subject: [PATCH] basic/fd-util: refuse "infinite" loop in close_all_fds()
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I had a test machine with ulimit -n set to 1073741816 through pam
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("session required pam_limits.so set_all", which copies the limits from PID 1,
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left over from testing of #10921).
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test-execute would "hang" and then fail with a timeout when running
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exec-inaccessiblepaths-proc.service. It turns out that the problem was in
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close_all_fds(), which would go to the fallback path of doing close()
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1073741813 times. Let's just fail if we hit this case. This only matters
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for cases where both /proc is inaccessible, and the *soft* limit has been
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raised.
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(gdb) bt
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#0 0x00007f7e2e73fdc8 in close () from target:/lib64/libc.so.6
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#1 0x00007f7e2e42cdfd in close_nointr ()
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from target:/home/zbyszek/src/systemd-work3/build-rawhide/src/shared/libsystemd-shared-241.so
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#2 0x00007f7e2e42d525 in close_all_fds ()
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from target:/home/zbyszek/src/systemd-work3/build-rawhide/src/shared/libsystemd-shared-241.so
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#3 0x0000000000426e53 in exec_child ()
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#4 0x0000000000429578 in exec_spawn ()
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#5 0x00000000004ce1ab in service_spawn ()
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#6 0x00000000004cff77 in service_enter_start ()
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#7 0x00000000004d028f in service_enter_start_pre ()
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#8 0x00000000004d16f2 in service_start ()
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#9 0x00000000004568f4 in unit_start ()
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#10 0x0000000000416987 in test ()
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#11 0x0000000000417632 in test_exec_inaccessiblepaths ()
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#12 0x0000000000419362 in run_tests ()
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#13 0x0000000000419632 in main ()
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(cherry picked from commit 6a461d1f59850ff27bd254a3b71fe9ade0523e76)
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Related: RHEL-18302
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---
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src/basic/fd-util.c | 11 +++++++++++
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1 file changed, 11 insertions(+)
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diff --git a/src/basic/fd-util.c b/src/basic/fd-util.c
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index fea93d2039..5d0df11d7e 100644
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--- a/src/basic/fd-util.c
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+++ b/src/basic/fd-util.c
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@@ -24,6 +24,10 @@
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#include "stdio-util.h"
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#include "util.h"
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+/* The maximum number of iterations in the loop to close descriptors in the fallback case
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+ * when /proc/self/fd/ is inaccessible. */
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+#define MAX_FD_LOOP_LIMIT (1024*1024)
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+
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int close_nointr(int fd) {
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assert(fd >= 0);
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@@ -227,6 +231,13 @@ int close_all_fds(const int except[], size_t n_except) {
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if (max_fd < 0)
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return max_fd;
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+ /* Refuse to do the loop over more too many elements. It's better to fail immediately than to
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+ * spin the CPU for a long time. */
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+ if (max_fd > MAX_FD_LOOP_LIMIT)
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+ return log_debug_errno(EPERM,
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+ "/proc/self/fd is inaccessible. Refusing to loop over %d potential fds.",
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+ max_fd);
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+
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for (fd = 3; fd >= 0; fd = fd < max_fd ? fd + 1 : -1) {
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int q;
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