2019-03-30 14:01:40

by Nikitas Angelinas

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

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 <[email protected]>
Reported-by: [email protected]
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

2019-03-30 16:17:57

by Mukesh Ojha

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

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 <[email protected]>
> Reported-by: [email protected]
> 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 <[email protected]>


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