* Re: [PATCH] fs: prevent double-free on an error path in core dumper
[not found] <1347380162-2359-1-git-send-email-vda.linux@googlemail.com>
@ 2012-09-11 15:59 ` Oleg Nesterov
2012-09-12 5:06 ` Cong Wang
2012-09-12 11:33 ` Denys Vlasenko
0 siblings, 2 replies; 3+ messages in thread
From: Oleg Nesterov @ 2012-09-11 15:59 UTC (permalink / raw)
To: Denys Vlasenko; +Cc: linux-kernel, Andrew Morton, Amerigo Wang, Roland McGrath
Denys, let's not discuss this offlist... add lkml/cc's
On 09/11, Denys Vlasenko wrote:
>
> If elf_note_info_init fails to allocate memory for info->fields,
> it frees already alloceted stuff and returns error to its caller,
> fill_note_info. Which in turn returns error to its caller,
> elf_core_dump. Which jumps to cleanup label and calls free_note_info,
> which will happily try to free all info->fields again. BOOM.
This is !CORE_DUMP_USE_REGSET case, please mention this in the
changelog. And s/fs:/coredump:/ in the subject ;)
OK, I think you are right, but unless I missed something there
is a better fix.
> This is the fix.
>
> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
> ---
> fs/binfmt_elf.c | 4 +++-
> 1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 760d7f5..b2b7034 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -1617,7 +1617,7 @@ static void free_note_info(struct elf_note_info *info)
> kfree(info->psinfo.data);
> }
>
> -#else
> +#else /* !CORE_DUMP_USE_REGSET */
>
> /* Here is the structure in which status of each thread is captured. */
> struct elf_thread_status
> @@ -1718,6 +1718,8 @@ static int elf_note_info_init(struct elf_note_info *info)
> kfree(info->psinfo);
> notes_free:
> kfree(info->notes);
> + /* The caller will try to clean us up again, must set ptrs to NULL */
Exactly. The caller will do free_note_info() and info was zeroed at the
start. See below
> + memset(info, 0, sizeof(*info));
Yes, this will fix the problem.
But, again, the caller does free_note_info(), so why elf_note_info_init()
tries to handle the kmalloc failures? Afaics, we can simplify the code
and fix the bug.
What do you think about the patch below?
Oleg.
--- x/fs/binfmt_elf.c
+++ x/fs/binfmt_elf.c
@@ -1696,30 +1696,19 @@ static int elf_note_info_init(struct elf
return 0;
info->psinfo = kmalloc(sizeof(*info->psinfo), GFP_KERNEL);
if (!info->psinfo)
- goto notes_free;
+ return 0;
info->prstatus = kmalloc(sizeof(*info->prstatus), GFP_KERNEL);
if (!info->prstatus)
- goto psinfo_free;
+ return 0;
info->fpu = kmalloc(sizeof(*info->fpu), GFP_KERNEL);
if (!info->fpu)
- goto prstatus_free;
+ return 0;
#ifdef ELF_CORE_COPY_XFPREGS
info->xfpu = kmalloc(sizeof(*info->xfpu), GFP_KERNEL);
if (!info->xfpu)
- goto fpu_free;
+ return 0;
#endif
return 1;
-#ifdef ELF_CORE_COPY_XFPREGS
- fpu_free:
- kfree(info->fpu);
-#endif
- prstatus_free:
- kfree(info->prstatus);
- psinfo_free:
- kfree(info->psinfo);
- notes_free:
- kfree(info->notes);
- return 0;
}
static int fill_note_info(struct elfhdr *elf, int phdrs,
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