Re: [Feature Request?] Inline compression of process core dumps

Alan Cox
2007-04-13T12:36:04Z

> Looking at the code, it seems to me that format_corename() is appending
> .pid, regardless if !core_uses_pid and corename[0]=='|', in which case
> it creates an invalid path for call_usermodehelper_pipe().
>
> Bug in the code, or bug in my methods?

This looks somewhat better and might do the trick. Also fixes a very very
obscure security corner case. If you change core pattern to start with
the program name then the user can run a program called "|myevilhack" as
it stands. The patch checks for "|" in the pattern not the output and
doesn't nail a pid on to a piped name.

Signed-off-by: Alan Cox <alan@redhat.com>

diff -u --exclude-from /usr/src/exclude --new-file --recursive linux.vanilla-2.6.21-rc6-mm1/fs/exec.c linux-2.6.21-rc6-mm1/fs/exec.c
--- linux.vanilla-2.6.21-rc6-mm1/fs/exec.c 2007-04-12 14:15:05.000000000 +0100
+++ linux-2.6.21-rc6-mm1/fs/exec.c 2007-04-13 13:11:20.709835952 +0100
@@ -1265,13 +1265,17 @@
* name into corename, which must have space for at least
* CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
*/
-static void format_corename(char *corename, const char *pattern, long signr)
+static int format_corename(char *corename, const char *pattern, long signr)
{
const char *pat_ptr = pattern;
char *out_ptr = corename;
char *const out_end = corename + CORENAME_MAX_SIZE;
int rc;
int pid_in_pattern = 0;
+ int ispipe = 0;
+
+ if (*pattern == '|')
+ ispipe = 1;

/* Repeat as long as we have more pattern to process and more output
space */
@@ -1362,8 +1366,8 @@
*
* If core_pattern does not include a %p (as is the default)
* and core_uses_pid is set, then .%pid will be appended to
- * the filename */
- if (!pid_in_pattern
+ * the filename. Do not do this for piped commands. */
+ if (!ispipe && !pid_in_pattern
&& (core_uses_pid || atomic_read(&current->mm->mm_users) != 1)) {
rc = snprintf(out_ptr, out_end - out_ptr,
".%d", current->tgid);
@@ -1371,8 +1375,9 @@
goto out;
out_ptr += rc;
}
- out:
+out:
*out_ptr = 0;
+ return ispipe;
}

static void zap_process(struct task_struct *start)
@@ -1523,16 +1528,15 @@
* uses lock_kernel()
*/
lock_kernel();
- format_corename(corename, core_pattern, signr);
+ ispipe = format_corename(corename, core_pattern, signr);
unlock_kernel();
- if (corename[0] == '|') {
+ if (ispipe) {
/* SIGPIPE can happen, but it's just never processed */
if(call_usermodehelper_pipe(corename+1, NULL, NULL, &file)) {
printk(KERN_INFO "Core dump to %s pipe failed\n",
corename);
goto fail_unlock;
}
- ispipe = 1;
} else
file = filp_open(corename,
O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,