This is a note to let you know that I've just added the patch titled ACPI: custom_method: fix potential use-after-free issue to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: acpi-custom_method-fix-potential-use-after-free-issue.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From e483bb9a991bdae29a0caa4b3a6d002c968f94aa Mon Sep 17 00:00:00 2001 From: Mark Langsdorf <mlangsdo@xxxxxxxxxx> Date: Fri, 23 Apr 2021 10:28:17 -0500 Subject: ACPI: custom_method: fix potential use-after-free issue From: Mark Langsdorf <mlangsdo@xxxxxxxxxx> commit e483bb9a991bdae29a0caa4b3a6d002c968f94aa upstream. In cm_write(), buf is always freed when reaching the end of the function. If the requested count is less than table.length, the allocated buffer will be freed but subsequent calls to cm_write() will still try to access it. Remove the unconditional kfree(buf) at the end of the function and set the buf to NULL in the -EINVAL error path to match the rest of function. Fixes: 03d1571d9513 ("ACPI: custom_method: fix memory leaks") Signed-off-by: Mark Langsdorf <mlangsdo@xxxxxxxxxx> Cc: 5.4+ <stable@xxxxxxxxxxxxxxx> # 5.4+ Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/acpi/custom_method.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/acpi/custom_method.c +++ b/drivers/acpi/custom_method.c @@ -50,6 +50,7 @@ static ssize_t cm_write(struct file *fil (*ppos + count < count) || (count > uncopied_bytes)) { kfree(buf); + buf = NULL; return -EINVAL; } @@ -71,7 +72,6 @@ static ssize_t cm_write(struct file *fil add_taint(TAINT_OVERRIDDEN_ACPI_TABLE, LOCKDEP_NOW_UNRELIABLE); } - kfree(buf); return count; } Patches currently in stable-queue which might be from mlangsdo@xxxxxxxxxx are queue-4.4/acpi-custom_method-fix-a-possible-memory-leak.patch queue-4.4/acpi-custom_method-fix-potential-use-after-free-issue.patch