linux-kernel - [PATCH 4.19 30/58] libsubcmd: Fix use-after-free for realloc(..., 0)

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Date:   Mon, 21 Feb 2022 09:49:23 +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,
        Valdis Klētnieks <valdis.kletnieks@...edu>,
        Kees Kook <keescook@...omium.org>,
        "Justin M. Forbes" <jforbes@...oraproject.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-hardening@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 4.19 30/58] libsubcmd: Fix use-after-free for realloc(..., 0)

From: Kees Cook <keescook@...omium.org>

commit 52a9dab6d892763b2a8334a568bd4e2c1a6fde66 upstream.

GCC 12 correctly reports a potential use-after-free condition in the
xrealloc helper. Fix the warning by avoiding an implicit "free(ptr)"
when size == 0:

In file included from help.c:12:
In function 'xrealloc',
    inlined from 'add_cmdname' at help.c:24:2: subcmd-util.h:56:23: error: pointer may be used after 'realloc' [-Werror=use-after-free]
   56 |                 ret = realloc(ptr, size);
      |                       ^~~~~~~~~~~~~~~~~~
subcmd-util.h:52:21: note: call to 'realloc' here
   52 |         void *ret = realloc(ptr, size);
      |                     ^~~~~~~~~~~~~~~~~~
subcmd-util.h:58:31: error: pointer may be used after 'realloc' [-Werror=use-after-free]
   58 |                         ret = realloc(ptr, 1);
      |                               ^~~~~~~~~~~~~~~
subcmd-util.h:52:21: note: call to 'realloc' here
   52 |         void *ret = realloc(ptr, size);
      |                     ^~~~~~~~~~~~~~~~~~

Fixes: 2f4ce5ec1d447beb ("perf tools: Finalize subcmd independence")
Reported-by: Valdis Klētnieks <valdis.kletnieks@...edu>
Signed-off-by: Kees Kook <keescook@...omium.org>
Tested-by: Valdis Klētnieks <valdis.kletnieks@...edu>
Tested-by: Justin M. Forbes <jforbes@...oraproject.org>
Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: linux-hardening@...r.kernel.org
Cc: Valdis Klētnieks <valdis.kletnieks@...edu>
Link: http://lore.kernel.org/lkml/20220213182443.4037039-1-keescook@chromium.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 tools/lib/subcmd/subcmd-util.h |   11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

--- a/tools/lib/subcmd/subcmd-util.h
+++ b/tools/lib/subcmd/subcmd-util.h
@@ -50,15 +50,8 @@ static NORETURN inline void die(const ch
 static inline void *xrealloc(void *ptr, size_t size)
 {
 	void *ret = realloc(ptr, size);
-	if (!ret && !size)
-		ret = realloc(ptr, 1);
-	if (!ret) {
-		ret = realloc(ptr, size);
-		if (!ret && !size)
-			ret = realloc(ptr, 1);
-		if (!ret)
-			die("Out of memory, realloc failed");
-	}
+	if (!ret)
+		die("Out of memory, realloc failed");
 	return ret;
 }