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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Matthew Ruffell <matthew.ruffell@canonical.com>,
        Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Paul Wise <pabs3@bonedaddy.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Neil Horman <nhorman@tuxdriver.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 5.6 099/167] coredump: fix null pointer dereference on coredump
Date:   Tue, 28 Apr 2020 20:24:35 +0200
Message-Id: <20200428182237.696357713@linuxfoundation.org>
In-Reply-To: <20200428182225.451225420@linuxfoundation.org>
References: <20200428182225.451225420@linuxfoundation.org>
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From: Sudip Mukherjee <sudipm.mukherjee@gmail.com>

commit db973a7289dad24e6c017dcedc6aee886579dc3a upstream.

If the core_pattern is set to "|" and any process segfaults then we get
a null pointer derefernce while trying to coredump. The call stack shows:

    RIP: do_coredump+0x628/0x11c0

When the core_pattern has only "|" there is no use of trying the
coredump and we can check that while formating the corename and exit
with an error.

After this change I get:

    format_corename failed
    Aborting core

Fixes: 315c69261dd3 ("coredump: split pipe command whitespace before expanding template")
Reported-by: Matthew Ruffell <matthew.ruffell@canonical.com>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Wise <pabs3@bonedaddy.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200416194612.21418-1-sudipm.mukherjee@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -211,6 +211,8 @@ static int format_corename(struct core_n
 			return -ENOMEM;
 		(*argv)[(*argc)++] = 0;
 		++pat_ptr;
+		if (!(*pat_ptr))
+			return -ENOMEM;
 	}
 
 	/* Repeat as long as we have more pattern to process and more output