linux-kernel - Re: [PATCH] fs/read_write.c: Fix memory leak in read

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Date:   Wed, 24 Jun 2020 04:24:47 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Peng Fan <fanpeng@...ngson.cn>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>
Subject: Re: [PATCH] fs/read_write.c: Fix memory leak in read_write.c

On Wed, Jun 24, 2020 at 11:07:03AM +0800, Peng Fan wrote:
> kmemleak report:
> unreferenced object 0x98000002bb591d00 (size 256):
>   comm "ftest03", pid 24778, jiffies 4301603810 (age 490.665s)
>   hex dump (first 32 bytes):
>     00 01 04 20 01 00 00 00 80 00 00 00 00 00 00 00  ... ............
>     f0 02 04 20 01 00 00 00 80 00 00 00 00 00 00 00  ... ............
>   backtrace:
>     [<0000000050b162cb>] __kmalloc+0x234/0x438
>     [<00000000491da9c7>] rw_copy_check_uvector+0x1ac/0x1f0
>     [<00000000b0dddb43>] import_iovec+0x50/0xe8
>     [<00000000ae843d73>] vfs_readv+0x50/0xb0
>     [<00000000c7216b06>] do_readv+0x80/0x160
>     [<00000000cad79c3f>] syscall_common+0x34/0x58
> 
> This is because "iov" allocated by kmalloc() is not destroyed. Under normal
> circumstances, "ret_pointer" should be equal to "iov". But if the previous 
> statements fails to execute, and the allocation is successful, then the
> block of memory will not be released, because it is necessary to 
> determine whether they are equal. So we need to change the order.

This patch doesn't make sense.  It will _introduce_ a memory leak,
not fix one.