[PATCH] fs/binfmt_elf.c: fix GPF when dereferencing invalid interpreter

[PATCH] fs/binfmt_elf.c: fix GPF when dereferencing invalid interpreter

[Nikitas Angelinas]

Syzkaller found an issue where an invalid interpreter pointer is
dereferenced in load_elf_binary()->allow_write_access(). 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.

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")
---
 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
-- 
2.10.0

Re: [PATCH] fs/binfmt_elf.c: fix GPF when dereferencing invalid interpreter

[Mukesh Ojha]

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