linux-kernel - [PATCH 4.19 220/247] x86: fix seq_file iteration for pat/memtype.c

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Message-Id: <20210301161042.449644211@linuxfoundation.org>
Date:   Mon,  1 Mar 2021 17:14:00 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, NeilBrown <neilb@...e.de>,
        Xin Long <lucien.xin@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vlad Yasevich <vyasevich@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.19 220/247] x86: fix seq_file iteration for pat/memtype.c

From: NeilBrown <neilb@...e.de>

commit 3d2fc4c082448e9c05792f9b2a11c1d5db408b85 upstream.

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.

Link: https://lkml.kernel.org/r/161248539022.21478.13874455485854739066.stgit@noble1
Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface")
Signed-off-by: NeilBrown <neilb@...e.de>
Cc: Xin Long <lucien.xin@...il.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Jonathan Corbet <corbet@....net>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc: Neil Horman <nhorman@...driver.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Vlad Yasevich <vyasevich@...il.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/mm/pat.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -1131,12 +1131,14 @@ static void *memtype_seq_start(struct se
 
 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)
@@ -1145,7 +1147,6 @@ static int memtype_seq_show(struct seq_f
 
 	seq_printf(seq, "%s @ 0x%Lx-0x%Lx\n", cattr_name(print_entry->type),
 			print_entry->start, print_entry->end);
-	kfree(print_entry);
 
 	return 0;
 }