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Subject[PATCH v4] core_pattern: fix long parameters was truncated by core_pattern handler
Date
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 v3:
make handling of single char also uses cn_printf, suggested by Andrew Morton.

Changes since v2:
Introduced generic function cn_printf and make format_corename remember the time
has been expanded, suggested by Olg Nesterov and Neil Horman.

Changes since v1:
This patch allocates corename at runtime, if the replace doesn't have enough
memory, expand the corename dynamically, suggested by Neil Horman.

I've tested with some core_pattern strings, it works fine now.

Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Neil Horman <nhorman@tuxdriver.com>
Cc: Roland McGrath <roland@redhat.com>
---
fs/exec.c | 158 +++++++++++++++++++++++++++++++++++++-----------------------
1 files changed, 97 insertions(+), 61 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 2d94552..0151923 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -65,6 +65,12 @@ char core_pattern[CORENAME_MAX_SIZE] = "core";
unsigned int core_pipe_limit;
int suid_dumpable = 0;

+struct core_name {
+ char *corename;
+ int used, size;
+};
+static atomic_t call_count = ATOMIC_INIT(1);
+
/* The maximal length of core_pattern is also specified in sysctl.c */

static LIST_HEAD(formats);
@@ -1440,127 +1446,149 @@ void set_binfmt(struct linux_binfmt *new)

EXPORT_SYMBOL(set_binfmt);

+static int expand_corename(struct core_name *cn)
+{
+ char *old_corename = cn->corename;
+
+ cn->size = CORENAME_MAX_SIZE * atomic_inc_return(&call_count);
+ cn->corename = krealloc(old_corename, cn->size, GFP_KERNEL);
+
+ if (!cn->corename) {
+ kfree(old_corename);
+ return -ENOMEM;
+ }
+
+ return 0;
+}
+
+static int cn_printf(struct core_name *cn, const char *fmt, ...)
+{
+ char *cur;
+ int need;
+ int ret;
+ va_list arg;
+
+ va_start(arg, fmt);
+ need = vsnprintf(NULL, 0, fmt, arg);
+ va_end(arg);
+
+ if (likely(need < cn->size - cn->used))
+ goto out_printf;
+
+ ret = expand_corename(cn);
+ if (ret)
+ goto expand_fail;
+
+out_printf:
+ cur = cn->corename + cn->used;
+ va_start(arg, fmt);
+ vsnprintf(cur, need + 1, fmt, arg);
+ va_end(arg);
+ cn->used += need;
+ return 0;
+
+expand_fail:
+ return ret;
+}
+
/* format_corename will inspect the pattern parameter, and output a
* name into corename, which must have space for at least
* CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
*/
-static int format_corename(char *corename, long signr)
+static int format_corename(struct core_name *cn, long signr)
{
const struct cred *cred = current_cred();
const char *pat_ptr = core_pattern;
int ispipe = (*pat_ptr == '|');
- char *out_ptr = corename;
- char *const out_end = corename + CORENAME_MAX_SIZE;
- int rc;
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)
+ return -ENOMEM;

/* Repeat as long as we have more pattern to process and more output
space */
while (*pat_ptr) {
if (*pat_ptr != '%') {
- if (out_ptr == out_end)
- goto out;
- *out_ptr++ = *pat_ptr++;
+ err = cn_printf(cn, "%c", *pat_ptr++);
} else {
switch (*++pat_ptr) {
+ /* single % at the end, drop that */
case 0:
+ err = cn_printf(cn, "%c", '\0');
+ if (err)
+ break;
goto out;
/* Double percent, output one percent */
case '%':
- if (out_ptr == out_end)
- goto out;
- *out_ptr++ = '%';
+ err = cn_printf(cn, "%c", '%');
break;
/* pid */
case 'p':
pid_in_pattern = 1;
- rc = snprintf(out_ptr, out_end - out_ptr,
- "%d", task_tgid_vnr(current));
- if (rc > out_end - out_ptr)
- goto out;
- out_ptr += rc;
+ err = cn_printf(cn, "%d",
+ task_tgid_vnr(current));
break;
/* uid */
case 'u':
- rc = snprintf(out_ptr, out_end - out_ptr,
- "%d", cred->uid);
- if (rc > out_end - out_ptr)
- goto out;
- out_ptr += rc;
+ err = cn_printf(cn, "%d", cred->uid);
break;
/* gid */
case 'g':
- rc = snprintf(out_ptr, out_end - out_ptr,
- "%d", cred->gid);
- if (rc > out_end - out_ptr)
- goto out;
- out_ptr += rc;
+ err = cn_printf(cn, "%d", cred->gid);
break;
/* signal that caused the coredump */
case 's':
- rc = snprintf(out_ptr, out_end - out_ptr,
- "%ld", signr);
- if (rc > out_end - out_ptr)
- goto out;
- out_ptr += rc;
+ err = cn_printf(cn, "%ld", signr);
break;
/* UNIX time of coredump */
case 't': {
struct timeval tv;
do_gettimeofday(&tv);
- rc = snprintf(out_ptr, out_end - out_ptr,
- "%lu", tv.tv_sec);
- if (rc > out_end - out_ptr)
- goto out;
- out_ptr += rc;
+ err = cn_printf(cn, "%lu", tv.tv_sec);
break;
}
/* hostname */
case 'h':
down_read(&uts_sem);
- rc = snprintf(out_ptr, out_end - out_ptr,
- "%s", utsname()->nodename);
+ err = cn_printf(cn, "%s",
+ utsname()->nodename);
up_read(&uts_sem);
- if (rc > out_end - out_ptr)
- goto out;
- out_ptr += rc;
break;
/* executable */
case 'e':
- rc = snprintf(out_ptr, out_end - out_ptr,
- "%s", current->comm);
- if (rc > out_end - out_ptr)
- goto out;
- out_ptr += rc;
+ err = cn_printf(cn, "%s", current->comm);
break;
/* core limit size */
case 'c':
- rc = snprintf(out_ptr, out_end - out_ptr,
- "%lu", rlimit(RLIMIT_CORE));
- if (rc > out_end - out_ptr)
- goto out;
- out_ptr += rc;
+ err = cn_printf(cn, "%lu",
+ rlimit(RLIMIT_CORE));
break;
default:
break;
}
++pat_ptr;
}
+
+ if (err)
+ return err;
}
+
/* Backward compatibility with core_uses_pid:
*
* 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. Do not do this for piped commands. */
if (!ispipe && !pid_in_pattern && core_uses_pid) {
- rc = snprintf(out_ptr, out_end - out_ptr,
- ".%d", task_tgid_vnr(current));
- if (rc > out_end - out_ptr)
- goto out;
- out_ptr += rc;
+ err = cn_printf(cn, ".%d", task_tgid_vnr(current));
+ if (err)
+ return err;
}
out:
- *out_ptr = 0;
return ispipe;
}

@@ -1837,7 +1865,7 @@ static int umh_pipe_setup(struct subprocess_info *info)
void do_coredump(long signr, int exit_code, struct pt_regs *regs)
{
struct core_state core_state;
- char corename[CORENAME_MAX_SIZE + 1];
+ struct core_name cn;
struct mm_struct *mm = current->mm;
struct linux_binfmt * binfmt;
const struct cred *old_cred;
@@ -1892,7 +1920,13 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
*/
clear_thread_flag(TIF_SIGPENDING);

- ispipe = format_corename(corename, signr);
+ ispipe = format_corename(&cn, signr);
+
+ if (ispipe == -ENOMEM) {
+ printk(KERN_WARNING "format_corename failed\n");
+ printk(KERN_WARNING "Aborting core\n");
+ goto fail_corename;
+ }

if (ispipe) {
int dump_count;
@@ -1929,7 +1963,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
goto fail_dropcount;
}

- helper_argv = argv_split(GFP_KERNEL, corename+1, NULL);
+ helper_argv = argv_split(GFP_KERNEL, cn.corename+1, NULL);
if (!helper_argv) {
printk(KERN_WARNING "%s failed to allocate memory\n",
__func__);
@@ -1942,7 +1976,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
argv_free(helper_argv);
if (retval) {
printk(KERN_INFO "Core dump to %s pipe failed\n",
- corename);
+ cn.corename);
goto close_fail;
}
} else {
@@ -1951,7 +1985,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
if (cprm.limit < binfmt->min_coredump)
goto fail_unlock;

- cprm.file = filp_open(corename,
+ cprm.file = filp_open(cn.corename,
O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
0600);
if (IS_ERR(cprm.file))
@@ -1993,6 +2027,8 @@ fail_dropcount:
if (ispipe)
atomic_dec(&core_dump_count);
fail_unlock:
+ kfree(cn.corename);
+fail_corename:
coredump_finish(mm);
revert_creds(old_cred);
fail_creds:
--
1.7.2.1


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