Linux-Fsdevel Archive on lore.kernel.org
help / color / mirror / Atom feed
* NULL pointer dereference in coredump code
@ 2020-03-30  8:31 Thibaut Sautereau
  2020-05-19  7:16 ` Thibaut Sautereau
  0 siblings, 1 reply; 2+ messages in thread
From: Thibaut Sautereau @ 2020-03-30  8:31 UTC (permalink / raw)
  To: Alexander Viro, linux-fsdevel, linux-kernel

[-- Attachment #1: Type: text/plain, Size: 944 bytes --]

I hit a kernel NULL pointer dereference caused by the following call chain:

do_coredump()
  file_start_write(cprm.file) # cprm.file is NULL
    file_inode(file) # NULL ptr deref

The `ispipe` path is followed in do_coredump(), and:
    # cat /proc/sys/kernel/core_pattern
    |/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h

It seems that cprm.file can be NULL after the call to the usermode
helper, especially when setting CONFIG_STATIC_USERMODEHELPER=y and
CONFIG_STATIC_USERMODEHELPER_PATH="", which is the case for me.

One may say it's a strange combination of configuration options but I
think it should not crash the kernel anyway. As I don't know much about
coredumps in general and this code, I don't know what's the best way to
fix this issue in a clean and comprehensive way.

I attached the patch I used to temporarily work around this issue, if
that can clarify anything.

Thanks,

-- 
Thibaut Sautereau
CLIP OS developer

[-- Attachment #2: 0001-coredump-FIXUP.patch --]
[-- Type: text/plain, Size: 678 bytes --]

From 613dfc60429c1fc5fc19e1c8662648620dc103af Mon Sep 17 00:00:00 2001
From: Thibaut Sautereau <thibaut.sautereau@ssi.gouv.fr>
Date: Fri, 27 Mar 2020 16:34:59 +0100
Subject: [PATCH] coredump: FIXUP

---
 fs/coredump.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index b1ea7dfbd149..d0177b81345f 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -686,7 +686,7 @@ void do_coredump(const kernel_siginfo_t *siginfo)
 							  UMH_WAIT_EXEC);
 
 		kfree(helper_argv);
-		if (retval) {
+		if (retval || !cprm.file) {
 			printk(KERN_INFO "Core dump to |%s pipe failed\n",
 			       cn.corename);
 			goto close_fail;
-- 
2.26.0


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: NULL pointer dereference in coredump code
  2020-03-30  8:31 NULL pointer dereference in coredump code Thibaut Sautereau
@ 2020-05-19  7:16 ` Thibaut Sautereau
  0 siblings, 0 replies; 2+ messages in thread
From: Thibaut Sautereau @ 2020-05-19  7:16 UTC (permalink / raw)
  To: Alexander Viro, linux-fsdevel, linux-kernel

On Mon, Mar 30, 2020 at 10:31:59AM +0200, Thibaut Sautereau wrote:
> I hit a kernel NULL pointer dereference caused by the following call chain:
> 
> do_coredump()
>   file_start_write(cprm.file) # cprm.file is NULL
>     file_inode(file) # NULL ptr deref
> 
> The `ispipe` path is followed in do_coredump(), and:
>     # cat /proc/sys/kernel/core_pattern
>     |/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h
> 
> It seems that cprm.file can be NULL after the call to the usermode
> helper, especially when setting CONFIG_STATIC_USERMODEHELPER=y and
> CONFIG_STATIC_USERMODEHELPER_PATH="", which is the case for me.
> 
> One may say it's a strange combination of configuration options but I
> think it should not crash the kernel anyway. As I don't know much about
> coredumps in general and this code, I don't know what's the best way to
> fix this issue in a clean and comprehensive way.
> 
> I attached the patch I used to temporarily work around this issue, if
> that can clarify anything.
> 
> Thanks,

For the record, this had previously been reported [1] and was eventually
fixed by 3740d93e3790 ("coredump: fix crash when umh is disabled").

[1] https://bugzilla.kernel.org/show_bug.cgi?id=199795

-- 
Thibaut Sautereau
CLIP OS developer

^ permalink raw reply	[flat|nested] 2+ messages in thread

end of thread, other threads:[~2020-05-19  7:16 UTC | newest]

Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-30  8:31 NULL pointer dereference in coredump code Thibaut Sautereau
2020-05-19  7:16 ` Thibaut Sautereau

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).