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SubjectRE: [PATCH] coredump: prevent double-free on an error path in core dumper

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
> owner@vger.kernel.org] On Behalf Of Denys Vlasenko
> Sent: Wednesday, September 12, 2012 5:07 PM
> To: Oleg Nesterov; linux-kernel@vger.kernel.org; Andrew Morton; Roland
> McGrath
> Cc: Denys Vlasenko
> Subject: [PATCH] coredump: prevent double-free on an error path in core
> dumper
>
> In !CORE_DUMP_USE_REGSET case, if elf_note_info_init fails to allocate
> memory
> for info->fields, it frees already allocated 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 the fix.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
> ---
> fs/binfmt_elf.c | 19 ++++---------------
> 1 files changed, 4 insertions(+), 15 deletions(-)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 760d7f5..1b4efbc 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -1695,30 +1695,19 @@ static int elf_note_info_init(struct elf_note_info
> *info)
> return 0;
> info->psinfo = kmalloc(sizeof(*info->psinfo), GFP_KERNEL);

Why don't you change kmalloc to devm_kzalloc, so that free can be ignored altogether.

> 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,
> --
> 1.7.7.6
>
> --
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