linux-kernel - [PATCH 2/3] x86: fix seq_file iteration for pat/memtype.c

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Message-ID: <161248539022.21478.13874455485854739066.stgit@noble1>
Date:   Fri, 05 Feb 2021 11:36:30 +1100
From:   NeilBrown <neilb@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Xin Long <lucien.xin@...il.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] x86: fix seq_file iteration for pat/memtype.c

The memtype seq_file iterator allocates a buffer in the ->start and
->next functions and frees it in the ->show function.
The preferred handling for such resources is to free them in the
subsequent ->next or ->stop function call.

Since Commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration
code and interface") there is no guarantee that ->show will be called
after ->next, so this function can now leak memory.

So move the freeing of the buffer to ->next and ->stop.

Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface")
Cc: Xin Long <lucien.xin@...il.com>
Signed-off-by: NeilBrown <neilb@...e.de>
---
 arch/x86/mm/pat/memtype.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c
index 8f665c352bf0..ca311aaa67b8 100644
--- a/arch/x86/mm/pat/memtype.c
+++ b/arch/x86/mm/pat/memtype.c
@@ -1164,12 +1164,14 @@ static void *memtype_seq_start(struct seq_file *seq, loff_t *pos)
 
 static void *memtype_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
+	kfree(v);
 	++*pos;
 	return memtype_get_idx(*pos);
 }
 
 static void memtype_seq_stop(struct seq_file *seq, void *v)
 {
+	kfree(v);
 }
 
 static int memtype_seq_show(struct seq_file *seq, void *v)
@@ -1181,8 +1183,6 @@ static int memtype_seq_show(struct seq_file *seq, void *v)
 			entry_print->end,
 			cattr_name(entry_print->type));
 
-	kfree(entry_print);
-
 	return 0;
 }