freebsd-dev/lib/libutil/kinfo_getfile.c
Conrad Meyer 14bdbaf2e4 Detect badly behaved coredump note helpers
Coredump notes depend on being able to invoke dump routines twice; once
in a dry-run mode to get the size of the note, and another to actually
emit the note to the corefile.

When a note helper emits a different length section the second time
around than the length it requested the first time, the kernel produces
a corrupt coredump.

NT_PROCSTAT_FILES output length, when packing kinfo structs, is tied to
the length of filenames corresponding to vnodes in the process' fd table
via vn_fullpath.  As vnodes may move around during dump, this is racy.

So:

 - Detect badly behaved notes in putnote() and pad underfilled notes.

 - Add a fail point, debug.fail_point.fill_kinfo_vnode__random_path to
   exercise the NT_PROCSTAT_FILES corruption.  It simply picks random
   lengths to expand or truncate paths to in fo_fill_kinfo_vnode().

 - Add a sysctl, kern.coredump_pack_fileinfo, to allow users to
   disable kinfo packing for PROCSTAT_FILES notes.  This should avoid
   both FILES note corruption and truncation, even if filenames change,
   at the cost of about 1 kiB in padding bloat per open fd.  Document
   the new sysctl in core.5.

 - Fix note_procstat_files to self-limit in the 2nd pass.  Since
   sometimes this will result in a short write, pad up to our advertised
   size.  This addresses note corruption, at the risk of sometimes
   truncating the last several fd info entries.

 - Fix NT_PROCSTAT_FILES consumers libutil and libprocstat to grok the
   zero padding.

With suggestions from:	bjk, jhb, kib, wblock
Approved by:	markj (mentor)
Relnotes:	yes
Sponsored by:	EMC / Isilon Storage Division
Differential Revision:	https://reviews.freebsd.org/D3548
2015-09-03 20:32:10 +00:00

78 lines
1.4 KiB
C

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/user.h>
#include <sys/sysctl.h>
#include <stdlib.h>
#include <string.h>
#include "libutil.h"
struct kinfo_file *
kinfo_getfile(pid_t pid, int *cntp)
{
int mib[4];
int error;
int cnt;
size_t len;
char *buf, *bp, *eb;
struct kinfo_file *kif, *kp, *kf;
*cntp = 0;
len = 0;
mib[0] = CTL_KERN;
mib[1] = KERN_PROC;
mib[2] = KERN_PROC_FILEDESC;
mib[3] = pid;
error = sysctl(mib, 4, NULL, &len, NULL, 0);
if (error)
return (NULL);
len = len * 4 / 3;
buf = malloc(len);
if (buf == NULL)
return (NULL);
error = sysctl(mib, 4, buf, &len, NULL, 0);
if (error) {
free(buf);
return (NULL);
}
/* Pass 1: count items */
cnt = 0;
bp = buf;
eb = buf + len;
while (bp < eb) {
kf = (struct kinfo_file *)(uintptr_t)bp;
if (kf->kf_structsize == 0)
break;
bp += kf->kf_structsize;
cnt++;
}
kif = calloc(cnt, sizeof(*kif));
if (kif == NULL) {
free(buf);
return (NULL);
}
bp = buf;
eb = buf + len;
kp = kif;
/* Pass 2: unpack */
while (bp < eb) {
kf = (struct kinfo_file *)(uintptr_t)bp;
if (kf->kf_structsize == 0)
break;
/* Copy/expand into pre-zeroed buffer */
memcpy(kp, kf, kf->kf_structsize);
/* Advance to next packed record */
bp += kf->kf_structsize;
/* Set field size to fixed length, advance */
kp->kf_structsize = sizeof(*kp);
kp++;
}
free(buf);
*cntp = cnt;
return (kif); /* Caller must free() return value */
}