[PATCH 1/1] coredump: Fix null pointer dereference when kernel.core_pattern is "|"

From: Matthew Ruffell
Date: Thu Feb 20 2020 - 00:10:32 EST

Since 315c692, a null pointer dereference can be triggered when the
kernel.core_pattern string is set to "|", and a user executes a program which

This is caused by a subtle change in parameters sent to
call_usermodehelper_exec(), as sub_info->path will be set to cn.corename, which
has not changed from its initial value of '\0'. call_usermodehelper_exec()
will return 0 upon strlen() finding that sub_info->path has zero length.

The fix is to add a length check for cn.corename when we check the return code
from call_usermodehelper_exec(). This restores the expected semantics as seen
before 315c692, with the message "Core dump to | pipe failed" output to dmesg
and the coredump being aborted.

Fixes: 315c692 ("coredump: split pipe command whitespace before expanding template")
Signed-off-by: Matthew Ruffell <matthew.ruffell@xxxxxxxxxxxxx>
fs/coredump.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index b1ea7dfbd149..ca5976e81d8a 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -686,7 +686,7 @@ void do_coredump(const kernel_siginfo_t *siginfo)

- if (retval) {
+ if (retval || strlen(cn.corename) == 0) {
printk(KERN_INFO "Core dump to |%s pipe failed\n",
goto close_fail;