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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id be3sm1732780pfb.8.2022.02.12.10.18.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 12 Feb 2022 10:18:58 -0800 (PST) From: Kees Cook To: Josh Poimboeuf Cc: Kees Cook , =?UTF-8?q?Valdis=20Kl=C4=93tnieks?= , Justin Forbes , Arnaldo Carvalho de Melo , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH] tools: Fix use-after-free for realloc(..., 0) Date: Sat, 12 Feb 2022 10:18:55 -0800 Message-Id: <20220212181855.3460176-1-keescook@chromium.org> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Developer-Signature: v=1; a=openpgp-sha256; l=2421; h=from:subject; bh=gfLUG5BRezAorsaD9PFyU6JfAQleA4jtrlj/yPG8KgQ=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBiB/oOw13KMvgwrXOUcUWhx2qwZdic+XCBaPRZuNle 3v/q4gSJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCYgf6DgAKCRCJcvTf3G3AJliGEA CPJbWUnU77KPt05mNov2PU2yIbEjoGAHbScRRD5xZ+aoGVqtFIJacn/bUUZFzUAJTn6mbac8y+MhOq 6jt0x2XUG+HU8qy2i/a8467JRqDJjf/SyB3CYdfGJQyZazgn9mhtu0Tt2S3TltzW6Ao2E9sS7dkd9q WHilTZ3qSheur+AjOVxl5rOU5n8YNOS6JgpZH6T82O+slddCVv+jD3jI0N9BX/FJXHffzWcI/qPOvF u7STCgaOVAx9IkyvMPFpwlXDjjY/z5KpzaafXlqKs0KMmAYhZET52VuPpcfosRukuGCM+GHqhxzXnY HzHcJoymblFkmp3bb8kQmtDnSZ9kEGWHYd7copV/IIS1mHEDQqIpvIaQvFrRcIPI3t4hVI/4wZX6h1 mmU2G2Yu/zEwvBYUQJXXLAQTaIMzrgoIFJsrNXyewZDY3Y9efhCpz7DTyFz1DYLN48QAdQhWN0JCgV dKKUIshraUI+QUcIHmcuCpkrExp2Q5grLN6jCewxn5HLrKKBuRohja+xxTA0bWJALCD8OV5Ev0yEWi Z5Ov+fLvQfKihSF6iryN7B2zhDVfvFb5yd9FVAsIQDKWix8dlVQGZLjTos3/m/S37QUbiPEQ1jSFRx K/6vMobG68d0w7/oUiJMmTItat0HREhbgzimr2DLRfzHsGQ6e736LQoHY6PQ== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org GCC 12 was correctly reporting 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); | ^~~~~~~~~~~~~~~~~~ Reported-by: "Valdis Klētnieks" Fixes: 2f4ce5ec1d44 ("perf tools: Finalize subcmd independence") Cc: Josh Poimboeuf Signed-off-by: Kees Cook --- tools/lib/subcmd/subcmd-util.h | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) diff --git a/tools/lib/subcmd/subcmd-util.h b/tools/lib/subcmd/subcmd-util.h index 794a375dad36..de392fc5fd3a 100644 --- a/tools/lib/subcmd/subcmd-util.h +++ b/tools/lib/subcmd/subcmd-util.h @@ -49,15 +49,24 @@ 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; + + /* + * Convert a zero-sized allocation into 1 byte, since + * realloc(ptr, 0) means free(ptr), but we don't want + * to release the memory. For a new allocation (when + * ptr == NULL), avoid triggering NULL-checking error + * conditions for zero-sized allocations. + */ + 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"); + /* + * If realloc() fails, the original block is left untouched; + * it is not freed or moved. + */ + die("Out of memory, realloc failed"); } return ret; } -- 2.30.2