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basic/process-util: only try PR_SET_MM once

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userwork wants to update the title many times, and a strace is full of
attempts that fail the same way:

[pid 21765] prctl(PR_SET_NAME, "systemd-userwor"...) = 0
[pid 21765] geteuid()                   = 0
[pid 21765] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fedce329000
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_START, 0x7fedce329000, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_END, 0x7fedce32901d, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] munmap(0x7fedce329000, 4096) = 0
[pid 21765] accept4(3, NULL, NULL, SOCK_CLOEXEC|SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
[pid 21765] prctl(PR_SET_NAME, "systemd-userwor"...) = 0
[pid 21765] geteuid()                   = 0
[pid 21765] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fedce329000
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_START, 0x7fedce329000, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_END, 0x7fedce329020, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] munmap(0x7fedce329000, 4096) = 0
[pid 21765] prctl(PR_SET_NAME, "systemd-userwor"...) = 0
[pid 21765] geteuid()                   = 0
[pid 21765] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fedce329000
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_START, 0x7fedce329000, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_END, 0x7fedce32901d, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] munmap(0x7fedce329000, 4096) = 0
[pid 21765] accept4(3, NULL, NULL, SOCK_CLOEXEC|SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
[pid 21765] prctl(PR_SET_NAME, "systemd-userwor"...) = 0
[pid 21765] geteuid()                   = 0
[pid 21765] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fedce329000
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_START, 0x7fedce329000, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_END, 0x7fedce329020, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] munmap(0x7fedce329000, 4096) = 0
[pid 21765] prctl(PR_SET_NAME, "systemd-userwor"...) = 0
[pid 21765] geteuid()                   = 0
[pid 21765] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fedce329000
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_START, 0x7fedce329000, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_END, 0x7fedce32901d, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] munmap(0x7fedce329000, 4096) = 0
[pid 21765] accept4(3, NULL, NULL, SOCK_CLOEXEC|SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
[pid 21765] prctl(PR_SET_NAME, "systemd-userwor"...) = 0
[pid 21765] geteuid()                   = 0
[pid 21765] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fedce329000
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_START, 0x7fedce329000, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] prctl(PR_SET_MM, PR_SET_MM_ARG_END, 0x7fedce329020, 0, 0) = -1 EPERM (Operation not permitted)
[pid 21765] munmap(0x7fedce329000, 4096) = 0

If we get a permission error, don't try again.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2020-05-22 09:23:31 +02:00
parent ad4f7f6747
commit c55104ce58
1 changed files with 10 additions and 0 deletions
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10
src/basic/process-util.c
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@ -207,6 +207,12 @@ int get_process_cmdline(pid_t pid, size_t max_columns, ProcessCmdlineFlags flags
}
static int update_argv(const char name[], size_t l) {
static int can_do = -1;
if (can_do == 0)
return 0;
can_do = false; /* We'll set it to true only if the whole process works */
/* Let's not bother with this if we don't have euid == 0. Strictly speaking we should check for the
* CAP_SYS_RESOURCE capability which is independent of the euid. In our own code the capability generally is
* present only for euid == 0, hence let's use this as quick bypass check, to avoid calling mmap() if
@ -233,6 +239,9 @@ static int update_argv(const char name[], size_t l) {
/* Now, let's tell the kernel about this new memory */
if (prctl(PR_SET_MM, PR_SET_MM_ARG_START, (unsigned long) nn, 0, 0) < 0) {
if (ERRNO_IS_PRIVILEGE(errno))
return log_debug_errno(errno, "PR_SET_MM_ARG_START failed: %m");
/* HACK: prctl() API is kind of dumb on this point. The existing end address may already be
* below the desired start address, in which case the kernel may have kicked this back due
* to a range-check failure (see linux/kernel/sys.c:validate_prctl_map() to see this in
@ -272,6 +281,7 @@ static int update_argv(const char name[], size_t l) {
log_debug_errno(errno, "PR_SET_MM_ARG_END failed, proceeding without: %m");
}
can_do = true;
return 0;
}