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Date:   Wed, 29 Apr 2020 23:49:51 +0200
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Subject: [PATCH v2 2/5] coredump: Let dump_emit() bail out on short writes
From:   Jann Horn <jannh@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Christoph Hellwig <hch@lst.de>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Russell King <linux@armlinux.org.uk>,
        linux-arm-kernel@lists.infradead.org,
        Mark Salter <msalter@redhat.com>,
        Aurelien Jacquiot <jacquiot.aurelien@gmail.com>,
        linux-c6x-dev@linux-c6x.org,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>, linux-sh@vger.kernel.org
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Sender: linux-kernel-owner@vger.kernel.org
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dump_emit() has a retry loop, but there seems to be no way for that retry
logic to actually be used; and it was also buggy, writing the same data
repeatedly after a short write.

Let's just bail out on a short write.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jann Horn <jannh@google.com>
---
 fs/coredump.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 408418e6aa131..d6fcc36a7db1f 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -823,17 +823,17 @@ int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
 	ssize_t n;
 	if (cprm->written + nr > cprm->limit)
 		return 0;
-	while (nr) {
-		if (dump_interrupted())
-			return 0;
-		n = __kernel_write(file, addr, nr, &pos);
-		if (n <= 0)
-			return 0;
-		file->f_pos = pos;
-		cprm->written += n;
-		cprm->pos += n;
-		nr -= n;
-	}
+
+
+	if (dump_interrupted())
+		return 0;
+	n = __kernel_write(file, addr, nr, &pos);
+	if (n != nr)
+		return 0;
+	file->f_pos = pos;
+	cprm->written += n;
+	cprm->pos += n;
+
 	return 1;
 }
 EXPORT_SYMBOL(dump_emit);
-- 
2.26.2.526.g744177e7f7-goog