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sysdeps: Only open oom_score_adj read/write if we need to write it

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If we're running in a sandbox, we might not have write access to
oom_score_adj. In the common case where we don't have any special
protection from the OOM-killer, we can detect that with only read
access, and skip the part where we open it for writing.

(We would also not have write access to oom_score_adj if we're running
with elevated Linux capabilities while not root, but that should never
actually happen for dbus-daemon-launch-helper, which is setuid root
for production use or has no capabilities during unit-testing.)

Signed-off-by: Simon McVittie <smcv@collabora.com>
(cherry picked from commit a8006841ce)
Backported-from: dbus!291
This commit is contained in:
Simon McVittie 2022-04-01 18:56:26 +01:00
parent aacd468108
commit a54da99a06
1 changed files with 23 additions and 3 deletions
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26
dbus/dbus-sysdeps-util-unix.c
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@ -1627,12 +1627,12 @@ _dbus_reset_oom_score_adj (const char **error_str_p)
const char *error_str = NULL;
#ifdef O_CLOEXEC
fd = open ("/proc/self/oom_score_adj", O_RDWR | O_CLOEXEC);
fd = open ("/proc/self/oom_score_adj", O_RDONLY | O_CLOEXEC);
#endif
if (fd < 0)
{
fd = open ("/proc/self/oom_score_adj", O_RDWR);
fd = open ("/proc/self/oom_score_adj", O_RDONLY);
if (fd >= 0)
_dbus_fd_set_close_on_exec (fd);
}
@ -1680,6 +1680,26 @@ _dbus_reset_oom_score_adj (const char **error_str_p)
goto out;
}
close (fd);
#ifdef O_CLOEXEC
fd = open ("/proc/self/oom_score_adj", O_WRONLY | O_CLOEXEC);
if (fd < 0)
#endif
{
fd = open ("/proc/self/oom_score_adj", O_WRONLY);
if (fd >= 0)
_dbus_fd_set_close_on_exec (fd);
}
if (fd < 0)
{
ret = FALSE;
error_str = "open(/proc/self/oom_score_adj) for writing";
saved_errno = errno;
goto out;
}
if (pwrite (fd, "0", sizeof (char), 0) < 0)
{
ret = FALSE;
@ -1700,7 +1720,7 @@ _dbus_reset_oom_score_adj (const char **error_str_p)
else
{
ret = FALSE;
error_str = "open(/proc/self/oom_score_adj)";
error_str = "open(/proc/self/oom_score_adj) for reading";
saved_errno = errno;
goto out;
}