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coredump: rely on /proc exclusively to get the name of the crashing process

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I couldn't see any reason why the kernel could provide COMM to the coredump
handler via the core_pattern command line but could not make it available in
/proc. So let's assume that this info is always available in /proc.

For "backtrace" mode (when --backtrace option is passed), I assumed that the
crashing process still exists at the time systemd-coredump is called.

Also changing the core_pattern line is an API breakage for any users of the
backtrace mode but given that systemd-coredump is installed in
/usr/lib/systemd, it's a private tool which has no internal users. At least no
one complained when the hostname was added to the core_pattern line
(f45b801551)...

Indeed it's much easier to get it from /proc since the kernel substitutes '%e'
specifier with multiple strings if the process name contains spaces (!).
This commit is contained in:
Franck Bui 2019-06-21 13:12:41 +02:00
parent 57ae8f9936
commit 47cf786c0a
2 changed files with 15 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
src/coredump/coredump.c
View File

@ -68,21 +68,14 @@
assert_cc(JOURNAL_SIZE_MAX <= DATA_SIZE_MAX);
enum {
/* We use this as array indexes for a couple of special fields we use for
* naming coredump files, and attaching xattrs, and for indexing argv[].
* Our pattern for man:systectl(1) kernel.core_pattern is such that the
* kernel passes fields until CONTEXT_RLIMIT as arguments in argv[]. After
* that it gets complicated: the kernel passes "comm" as one or more fields
* starting at index CONTEXT_COMM (in other words, full "comm" is under index
* CONTEXT_COMM when it does not contain spaces, which is the common
* case). This mapping is not reversible, so we prefer to retrieve "comm"
* from /proc. We only fall back to argv[CONTEXT_COMM...] when that fails.
/* We use this as array indexes for a couple of special fields we use for naming
* coredump files, and attaching xattrs, and for indexing argv[].
*
* In the internal context[] array, fields before CONTEXT_COMM are the
* strings from argv[], so they should not be freed. The strings at indices
* CONTEXT_COMM and higher are allocated by us and should be freed at the
* end.
* In the internal context[] array, fields before CONTEXT_COMM are the strings
* from argv[] passed by the kernel according to our pattern defined in
* /proc/sys/kernel/core_pattern (see man:core(5)). So they should not be
* freed. The strings at indices CONTEXT_COMM and higher are allocated by us and
* should be freed at the end.
*/
CONTEXT_PID,
CONTEXT_UID,
@ -1065,15 +1058,12 @@ static char* set_iovec_field_free(struct iovec *iovec, size_t *n_iovec, const ch
return x;
}
static int gather_pid_metadata(
char* context[_CONTEXT_MAX],
char **comm_fallback,
struct iovec *iovec, size_t *n_iovec) {
static int gather_pid_metadata(char *context[_CONTEXT_MAX], struct iovec *iovec, size_t *n_iovec) {
/* We need 27 empty slots in iovec!
*
* Note that if we fail on oom later on, we do not roll-back changes to the iovec structure. (It remains valid,
* with the first n_iovec fields initialized.) */
* Note that if we fail on oom later on, we do not roll-back changes to the iovec
* structure. (It remains valid, with the first n_iovec fields initialized.) */
uid_t owner_uid;
pid_t pid;
@ -1086,12 +1076,8 @@ static int gather_pid_metadata(
return log_error_errno(r, "Failed to parse PID \"%s\": %m", context[CONTEXT_PID]);
r = get_process_comm(pid, &context[CONTEXT_COMM]);
if (r < 0) {
log_warning_errno(r, "Failed to get COMM, falling back to the command line: %m");
context[CONTEXT_COMM] = strv_join(comm_fallback, " ");
if (!context[CONTEXT_COMM])
return log_oom();
}
if (r < 0)
return log_error_errno(r, "Failed to get COMM: %m");
r = get_process_exe(pid, &context[CONTEXT_EXE]);
if (r < 0)
@ -1234,7 +1220,7 @@ static int process_kernel(int argc, char* argv[]) {
context[CONTEXT_RLIMIT] = argv[1 + CONTEXT_RLIMIT];
context[CONTEXT_HOSTNAME] = argv[1 + CONTEXT_HOSTNAME];
r = gather_pid_metadata(context, argv + 1 + CONTEXT_COMM, iovec, &n_to_free);
r = gather_pid_metadata(context, iovec, &n_to_free);
if (r < 0)
goto finish;
@ -1295,7 +1281,7 @@ static int process_backtrace(int argc, char *argv[]) {
if (!iovec)
return log_oom();
r = gather_pid_metadata(context, argv + 2 + CONTEXT_COMM, iovec, &n_to_free);
r = gather_pid_metadata(context, iovec, &n_to_free);
if (r < 0)
goto finish;
if (r > 0) {

2
sysctl.d/50-coredump.conf.in
View File

@ -9,4 +9,4 @@
# and systemd-coredump(8) and core(5) for the explanation of the
# setting below.
kernel.core_pattern=|@rootlibexecdir@/systemd-coredump %P %u %g %s %t %c %h %e
kernel.core_pattern=|@rootlibexecdir@/systemd-coredump %P %u %g %s %t %c %h