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Subject: Re: [PATCH] fs/binfmt_elf.c: fix GPF when dereferencing invalid
 interpreter
To:     Nikitas Angelinas <nikitas.angelinas@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        syzbot+0d1fcd7268b21baced4a@syzkaller.appspotmail.com
References: <20190330140032.GA1527@vostro>
From:   Mukesh Ojha <mojha@codeaurora.org>
Message-ID: <47235084-9333-1096-e411-8d25ec120f30@codeaurora.org>
Date:   Sat, 30 Mar 2019 21:46:53 +0530
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On 3/30/2019 7:30 PM, Nikitas Angelinas wrote:
> Syzkaller found an issue where an invalid interpreter pointer is
> dereferenced in load_elf_binary()->allow_write_access()


please mention here on failure path inside  allow_write_access

as there are two path it gets called.


> . Fix this by
> jumping to a different label in the cleanup path.
>
> This patch applies against the latest linux-next tree. I have not tested
> that the patch addresses the issue, but it should, imho.


This should not be written in commit text body.
please fix.

>
> Signed-off-by: Nikitas Angelinas <nikitas.angelinas@gmail.com>
> Reported-by: syzbot+0d1fcd7268b21baced4a@syzkaller.appspotmail.com
> Fixes: 44e63c4a0263 ("fs/binfmt_elf.c: free PT_INTERP filename ASAP")
> ---


Patch looks valid to me as interpreter may be NULL and it later get 
tried to dereferencing inside allow_write_access

under label out_free_dentry.


Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>


Cheers,
-Mukesh

>   fs/binfmt_elf.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 51bc894..09e76b2 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -777,7 +777,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
>   			kfree(elf_interpreter);
>   			retval = PTR_ERR(interpreter);
>   			if (IS_ERR(interpreter))
> -				goto out_free_dentry;
> +				goto out_free_ph;
>   
>   			/*
>   			 * If the binary is not readable then enforce