Re: [RFC PATCH v3] core_pattern: fix long parameters was truncated by core_pattern handler

Andrew Morton
2010-08-23T21:19:13Z

On Fri, 20 Aug 2010 17:35:58 +0800
Xiaotian Feng <dfeng@redhat.com> wrote:

> We met a parameter truncated issue, consider following:
> > echo "|/root/core_pattern_pipe_test %p /usr/libexec/blah-blah-blah \
> %s %c %p %u %g 11 12345678901234567890123456789012345678 %t" > \
> /proc/sys/kernel/core_pattern
>
> This is okay because the strings is less than CORENAME_MAX_SIZE.
> "cat /proc/sys/kernel/core_pattern" shows the whole string. but
> after we run core_pattern_pipe_test in man page, we found last
> parameter was truncated like below:
> argc[10]=<12807486>
>
> The root cause is core_pattern allows % specifiers, which need to be
> replaced during parse time, but the replace may expand the strings
> to larger than CORENAME_MAX_SIZE. So if the last parameter is %
> specifiers, the replace code is using snprintf(out_ptr, out_end - out_ptr, ...),
> this will write out of corename array.
>
> Changes since v2:
> Introduced generic function cn_printf and make format_corename remember the time
> has been expanded.
>
> Changes since v1:
> This patch allocates corename at runtime, if the replace doesn't have enough
> memory, expand the corename dynamically.

> + if (cn->used == cn->size)
> + if (expand_corename(cn))
> + goto out_fail;
> +
> + out_ptr = cn->corename + cn->used;
> + *out_ptr = *pat_ptr++;
> + cn->used++;

> - if (out_ptr == out_end)
> - goto out;
> - *out_ptr++ = '%';
> + if (cn->used == cn->size)
> + if (expand_corename(cn))
> + goto out_fail;
> +
> + out_ptr = cn->corename + cn->used;
> + *out_ptr = '%';
> + cn->used++;

> + out_ptr = cn->corename + cn->used;
> + if (cn->used == cn->size)
> + if (expand_corename(cn))
> + goto out_fail;
> +
> + out_ptr = cn->corename + cn->used;
> *out_ptr = 0;

Quite a bit of code duplication there. A little helper function which
adds a single char to the output would tidy that up.

However I think that if the % and %% handers are converted to call
cn_printf() then the output is always null-terninated and the third
hunk of code above simply becomes unneeded?

Something like this, although I didn't try very hard. Just a
suggestion to work with ;)

fs/exec.c | 63 ++++++++++++++--------------------------------------
1 file changed, 17 insertions(+), 46 deletions(-)

diff -puN fs/exec.c~core_pattern-fix-long-parameters-was-truncated-by-core_pattern-handler-fix fs/exec.c
--- a/fs/exec.c~core_pattern-fix-long-parameters-was-truncated-by-core_pattern-handler-fix
+++ a/fs/exec.c
@@ -1503,89 +1503,66 @@ static int format_corename(struct core_n
int ispipe = (*pat_ptr == '|');
char *out_ptr;
int pid_in_pattern = 0;
+ int err = 0;

cn->size = CORENAME_MAX_SIZE * atomic_read(&call_count);
cn->corename = kmalloc(cn->size, GFP_KERNEL);
cn->used = 0;

if (!cn->corename)
- goto out_fail;
+ return -ENOMEM;

/* Repeat as long as we have more pattern to process and more output
space */
while (*pat_ptr) {
if (*pat_ptr != '%') {
- if (cn->used == cn->size)
- if (expand_corename(cn))
- goto out_fail;
-
- out_ptr = cn->corename + cn->used;
- *out_ptr = *pat_ptr++;
- cn->used++;
+ err = cn_printf(cn, "%c", *pat_ptr++);
} else {
switch (*++pat_ptr) {
case 0:
goto out;
/* Double percent, output one percent */
case '%':
- if (cn->used == cn->size)
- if (expand_corename(cn))
- goto out_fail;
-
- out_ptr = cn->corename + cn->used;
- *out_ptr = '%';
- cn->used++;
+ err = cn_printf(cn, "%%");
break;
/* pid */
case 'p':
pid_in_pattern = 1;
- if (cn_printf(cn, "%d",
- task_tgid_vnr(current)))
- goto out_fail;
+ err = cn_printf(cn, "%d",
+ task_tgid_vnr(current));
break;
/* uid */
case 'u':
- if (cn_printf(cn, "%d", cred->uid))
- goto out_fail;
+ err = cn_printf(cn, "%d", cred->uid);
break;
/* gid */
case 'g':
- if (cn_printf(cn, "%d", cred->gid))
- goto out_fail;
+ err = cn_printf(cn, "%d", cred->gid);
break;
/* signal that caused the coredump */
case 's':
- if (cn_printf(cn, "%ld", signr))
- goto out_fail;
+ err = cn_printf(cn, "%ld", signr);
break;
/* UNIX time of coredump */
case 't': {
struct timeval tv;
do_gettimeofday(&tv);
- if (cn_printf(cn, "%lu", tv.tv_sec))
- goto out_fail;
+ err = cn_printf(cn, "%lu", tv.tv_sec);
break;
}
/* hostname */
case 'h':
down_read(&uts_sem);
- if (cn_printf(cn, "%s",
- utsname()->nodename)) {
- up_read(&uts_sem);
- goto out_fail;
- }
+ err = cn_printf(cn, "%s", utsname()->nodename);
up_read(&uts_sem);
break;
/* executable */
case 'e':
- if (cn_printf(cn, "%s", current->comm))
- goto out_fail;
+ err = cn_printf(cn, "%s", current->comm);
break;
/* core limit size */
case 'c':
- if (cn_printf(cn, "%lu",
- rlimit(RLIMIT_CORE)))
- goto out_fail;
+ err = cn_printf(cn, "%lu", rlimit(RLIMIT_CORE));
break;
default:
break;
@@ -1593,6 +1570,10 @@ static int format_corename(struct core_n
++pat_ptr;
}
}
+
+ if (err)
+ return err;
+
/* Backward compatibility with core_uses_pid:
*
* If core_pattern does not include a %p (as is the default)
@@ -1603,17 +1584,7 @@ static int format_corename(struct core_n
goto out_fail;
}
out:
- out_ptr = cn->corename + cn->used;
- if (cn->used == cn->size)
- if (expand_corename(cn))
- goto out_fail;
-
- out_ptr = cn->corename + cn->used;
- *out_ptr = 0;
return ispipe;
-
-out_fail:
- return -ENOMEM;
}

static int zap_process(struct task_struct *start, int exit_code)
_