linux-kernel - [PATCH] Fix for gcc12 compile issues in ubcmd-util.h

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Date:   Fri, 28 Jan 2022 19:02:14 -0600
From:   "Justin M. Forbes" <jforbes@...oraproject.org>
To:     "Justin M. Forbes" <jforbes@...oraproject.org>,
        linux-kernel@...r.kernel.org
Cc:     jmforbes@...uxtx.org, Jakub Jelinek <jakub@...hat.com>
Subject: [PATCH] Fix for gcc12 compile issues in ubcmd-util.h

While the current code builds fine with gcc 11, it does not with gcc 12,
resulting in:

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);
      |                     ^~~~~~~~~~~~~~~~~~

The was mentioned in upstream gcc bug
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104069 where it was
determined that gcc was correct and the kernel needed to change.  This
fixes that use-after-free and makes things build again.

Signed-off-by: Justin M. Forbes <jforbes@...oraproject.org>
Cc: Jakub Jelinek <jakub@...hat.com>

---
 tools/lib/subcmd/subcmd-util.h | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/tools/lib/subcmd/subcmd-util.h b/tools/lib/subcmd/subcmd-util.h
index 794a375dad36..7009fc176636 100644
--- a/tools/lib/subcmd/subcmd-util.h
+++ b/tools/lib/subcmd/subcmd-util.h
@@ -49,13 +49,12 @@ static NORETURN inline void die(const char *err, ...)

 static inline void *xrealloc(void *ptr, size_t size)
 {
-	void *ret = realloc(ptr, size);
-	if (!ret && !size)
-		ret = realloc(ptr, 1);
+	void *ret;
+	if (!size)
+		size = 1;
+	ret = realloc(ptr, size);
 	if (!ret) {
 		ret = realloc(ptr, size);
-		if (!ret && !size)
-			ret = realloc(ptr, 1);
 		if (!ret)
 			die("Out of memory, realloc failed");
 	}
-- 
2.34.1